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With reference to the (adult) anatomy of the human heart:
The left atrium (LA) and the proximal part of the ascending aorta (Ao) abut one another, as shown nicely in this image . Is there a name for the wall(s) separating the LA and Ao? And is this a single structure (i.e. septum), or is there a sinus?
There isn't any particular structure there: you have the wall of the aorta/adventitia, and if you have an explanted heart there is a space and then the auricle of the left atrium on one side and the right atrium on the other. These would all be contained within the pericardium.
Where the aorta is most "touching" the left atrium is where the pulmonary veins come in: I think this picture from Gray is most helpful.
Figure 494. Henry Gray (1825-1861). Anatomy of the Human Body. 1918.
There really isn't much to distinguish these veins from the non-auricle part of the atrium, similar to the vena cava on the right side. If you were to cut along the veins eventually you would just open up into the atrium.
The Visible Heart Lab is another good reference http://www.vhlab.umn.edu/atlas/aorta for cardiac anatomy.
Answers-2, BIO 3220, Circulatory System
2. Review the general function of the circulatory system.
The general function of the circulatory system is for transportation of nutrients, gases, hormones, and waste. It also functions in immunity and temperature regulation.
3. Discuss the ontogeny and phylogeny of this system.
Concerning ontogeny, the developmental history of an organism, the circulatory system is the first system to be functional in development. There is similar embryology and phylogeny in all vertebrates. There is individual variation, however, in the circulatory system.
Concerning phylogeny, or evolutionary development, the systems of fish, amphibians, reptiles, birds and mammals show various stages of evolution. In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as “single circulation”. The heart of fish is therefore only a single pump (consisting of two chambers). In amphibians and reptiles “double circulation” is used, however the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart. Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers it is thought that the four-chambered heart of birds evolved independently of that of mammals.
4. Define plasma.
Plasma is the clear, yellowish fluid portion of blood, lymph, or intramuscular fluid in which cells are suspended. It differs from serum in that it contains fibrin and other soluble clotting elements.
5. List the three formed elements in blood and briefly discuss their functions.
Erythrocytes are red blood cells that transport oxygen and carbon dioxide to and from the tissues for example, hemoglobin that carries oxygen.
Leukocytes are white blood cells that help protect the body from infection and disease by aiding in immunity and antibody production. White blood cells include neutrophils, eosinophils, basophils, lymphocytes, and monocytes
Platelets (thrombocytes) are minute, nonnucleated, disklike cytoplasmic body found in the blood plasma of mammals that function to promote blood clotting.
6. Define hemopoiesis. Name the blood stem cell.
Hemopoiesis is the formation of blood or blood cells in the body. The blood stem cells are called hemocytoblasts.
7. Discuss the development of the heart.
The part of splanchnic layer of hypomere just posterior to pharynx and ventral to gut forms folds that fuse to form longitudinal tube. Four chambers are established that begin to contract in sequence. Embryonic heart is nearly a straight tube having four chambers that contract in sequence and pumps a single stream of unoxygenated blood forward in the body.
8. List the layers of the heart wall.
Endocardium, myocardium, epicardium
9. Name the membranes and cavity around the heart.
The parietal and visceral pericardium and the pericardial cavity
10. List the four heart parts of a gill breathing fish. Describe their single circuit of circulation.
In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as “single circulation.” The heart parts include the sinus venosus, the atrium, the ventricle, and the conus arteriosus.
11. Locate the heart valves and explain their purpose.
AV valve – one-way valve between the atrium and ventricle to prevent back flow of blood
Bicuspid valve – found in mammals composed of two triangular flaps located between the left atrium and left ventricle and regulates blood flow between these chambers
Tricuspid valve – found in mammals three-segmented valve of the heart that keeps blood in the right ventricle from flowing back into the right atrium
Semilunar valve – one-way valve between ventricle and conus arteriosus in gill breathing fish to prevent back flow of blood
Spiral valve – found in dipnoans and anurans attempts to divide conus arteriosus
Pulmonary/aortic valve – semilunar valves with semilunar cusps at the entrance to the pulmonary trunk from the right ventricle and aorta from left ventricle of the heart
12. Define bulbus arteriosus. Explain its function. Which animals possess it?
The bulbus arteriosus is the muscular expansion of ventral aorta to ensure steady blood flow in some fish. It is needed since the teleost conus arteriosus is short.
13. Describe the two-circuit heart of lungfish and amphibians. Address any significant changes in their hearts in comparison to the heart of gill breathing fish.
Lungfish and amphibians have a two-circuit heart. In the first circuit, the blood is pumped to the lungs, where it acquires oxygen. It then returns to the heart and enters the second circuit, going to the rest of the body, eventually returning to the heart. In comparison to gill breathing fish, they possess an interatrial septum, partial or complete, an interventrical septum, partial, and a spiral valve to divide the conus arteriosus.
14. List the heart chambers of the amniote heart.
Heart consists of 2 atria and 2 ventricles
15. Discuss the significance of the sinus venosus. Name the vertebrates that possess it.
The sinus venosus acts as the pacemaker for the heart. It is the first chamber in the heart of fish, amphibians, and reptiles, which receives blood from the veins and contracts to force the blood into the atrium. In birds and mammals, it becomes the sinoatrial node and acts as a pacemaker.
16. Characterize the SA node and name the vertebrates that possess it.
In birds and mammals, the sinus venosus becomes the sinoatrial node and acts as a pacemaker.
17. Depict the partitions and valves between amniote heart chambers.
The interatrial septum completely divides the atrium. The interventricular septum completely divides the ventricle in birds, crocodiles, and mammals. Located between the right atrium and right ventricle is the right atrioventricular (tricuspid) valve. Located between the right ventricle and pulmonary trunk is the pulmonary semilunar valve. Located between the left atrium and left ventricle is the left atrioventricular valve (bicuspid). Located between the left ventricle and aorta is the aortic semilunar valve.
18. Define auricle. Name those animals that have it.
The auricle of the heart is the earlobe-shaped process at the base of the heart and extending from the atria found in mammals only.
19. Trace the circulation through a typical amniote heart.
From body: deoxygenated blood flows through Vena cava (anterior and posterior) enter right atrium, to right ventricle, through pulmonary trunk to right and left pulmonary arteries to capillary beds in lungs
From lungs: oxygenated blood flows through pulmonary veins to left atrium to left ventricle through aorta to tissue capillary beds in body through vena cava to right atrium
20. Describe the basic pattern of arterial distribution. Identify which direction arterial blood travels.
Embryonic pattern is basically the same for all vertebrates. Heart pumps blood forward in ventral aorta (also called the truncus arteriosus). Aortic arches run upward through visceral arches. Dorsal aorta is the principal distributing vessel of body. Blood from anterior aortic arches runs forward in internal carotid arteries. Blood from posterior arches runs posteriorly into dorsal aorta where it is distributed by 3 sets of branches: dorsal branches, lateral branches, ventral branches. Arteries carry blood away from the heart.
21. Discuss the ventral aorta, arches, and circulatory routes in fish, include sharks, teleosts, and lungfish.
In fish, blood flows from heart through ventral aorta through 6 aortic arches past gills (capillaries, oxygen in, carbon dioxide out) and to dorsal aorta. Sharks possess a pseudobranchial artery, the efferent branchial artery of arch 1. In teleosts, the first and second arches are gone. Lungfish develop a pulmonary artery from the sixth aortic arch.
22. Describe the general pattern for tetrapod aortic arches. Distinguish the arches amongst amphibians, reptiles, birds and mammals.
General pattern for tetrapod aortic arches includes six arches developing in embryo with the first and second rapidly regressing. The third arch plus paired dorsal aortae create the internal carotid artery. The fifth aortic arch is not present in most. The sixth arch is the pulmonary artery. The common carotid artery arises from ventral aorta. The external carotid artery arises from common carotid artery. Urodeles have a ductus caroticus present and retain the fifth aortic arch. Anurans have no ductus caroticus present after metamorphosis. Reptiles have two aortic trunks and one pulmonary trunk (subdivisions of conus arteriosus). Birds and mammals have one aortic trunk from the third and fourth aortic arches and one pulmonary trunk from the sixth arch. The right fourth arch remains in birds. The left fourth arch remains in mammals. The subclavian artery in mammals forms from part of the right fourth arch. The ductus arteriosus is only present in the fetus of birds and mammals. For birds and mammals, the carotids are the same as the general pattern.
23. Identify the following arteries and discuss their derivatives:
Common carotid – runs upward in the neck and divides into the external and internal carotid arteries derived from ventral aorta
External carotid – the branch of the carotid artery that supplies blood to the face and tongue and external parts of the head derived from common carotid
Internal carotid – the branch of the carotid artery that supplies blood to the brain derived from the third aortic arch plus paired dorsal aortae
Right subclavian – a part of a major artery of the upper extremities or forelimbs that passes beneath the clavicle derived from part of the right fourth aortic arch
Pulmonary trunk – an arterial trunk with origin from the right ventricle of the heart, and dividing into the right and left pulmonary arteries, which enter the corresponding lungs and branch with the bronchi derived from the sixth aortic arch
Aortic trunk – the main trunk of the systemic arteries, carrying blood from the left side of the heart to the arteries of all limbs and organs except the lungs derived from the third and fourth aortic arches
Ductus arteriosus – a short broad vessel in the fetus that connects the pulmonary artery with the aorta and conducts most of the blood directly from the right ventricle to the aorta bypassing the lungs
Ductus caroticus – a portion of the embryonic dorsal aorta between points of juncture with the third and fourth arch arteries it disappears early in development
24. Describe the general pattern of the dorsal aorta, including the following branches: visceral branches, lateral visceral branches, and somatic branches.
Dorsal aorta – extends into tail as caudal artery ventral visceral branches include celiac artery to stomach, liiver and pancreas, mesenteric arteries to rest of gut (small and large intestine) lateral visceral branches go to urogenital organs dorsal somatic branches to spinal cord, muscles, and skin subclavian arteries to pectoral appendages as branchial arteries iliac arteries to pelvic appendages as femoral arteries
25. Characterize the venous blood flow patterns in the vertebrates, including the following streams: cardinal stream, renal portal stream, hepatic portal stream, and lateral abdominal stream.
The venous channels in sharks:
Cardinal streams – sinus venosus receives all blood returning to heart. Most blood enters sinus venosus via Common Cardinals. Blood from head is collected by Anterior Cardinals. Postcardinals receive renal veins & empty into Common Cardinals.
Renal Portal stream – Early in development, some blood from caudal vein continue forward as Subintestinal (drains digestive system) this connection is then lost. During development, afferent renal veins (from old postcardinals) invade kidneys, & old postcardinals near top of kidneys are lost all blood from tail must now enter kidney capillaries.
Lateral Abdominal stream – LA vein starts at pelvic fin (where it receives iliac vein) & passes along lateral body wall receives brachial vein, then turns, becomes Subclavian vein, & enters Common Cardinal vein.
Hepatic Portal stream & Hepatic sinuses – Among 1st vessels to appear in vertebrate embryos are Vitelline veins (from yolk sac to heart). One Vitelline vein joins with embryonic Subintestinal vein (that drains digestive system) & becomes the Hepatic Portal System. Between liver & sinus venosus, 2 Vitelline veins are known as Hepatic sinuses.
Venous channels in other fishes are much like those of sharks except:
Cyclostomes have no renal portals
In most bony fishes the lateral abdominals are absent & the pelvic fins are drained by postcardinals
Venous channels of tetrapods – early embryonic venous channels are very similar to those of embryonic sharks. Changes during development include:
Cardinal veins & precavae – embryonic tetrapods have posterior cardinals, anterior cardinals, & common cardinals
Urodeles – posterior cardinals persist between caudal vein & common cardinals in adults
Anurans, most reptiles, & birds – posterior cardinals are lost anterior to kidneys
Mammals – right posterior cardinal persists (azygos) part of left posterior cardinal persists (hemiazygos)
Some mammals (e.g., cats & humans) lose the left precava the left brachiocephalic carries blood from left side to right precava
Early tetrapod embryos – paired lateral veins (like lateral abdominals of sharks) begin in caudal body wall near hind limbs, continue cranially, receive veins from forelimbs, & empty into cardinal veins or sinus venosus. As development continues:
Amphibians – 2 abdominal veins fuse at midventral line & form ventral abdominal vein. Blood in this vessel goes into liver capillaries & abdominals anterior to liver are lost (so abdominal stream no longer drains anterior limbs).
Reptiles – 2 lateral abdominals do not fuse but still terminate in liver capillaries (so do not drain anterior limbs see diagram below).
Birds – retain none of their embryonic abdominal stream as adults Mammals – no abdominal stream in adults
Renal Portal system:
Amphibians & some reptiles – acquires a tributary (external iliac vein not homologous to mammalian external iliac) which carries some blood from the hind limbs to the renal portal vein. This channel provides an alternate route from the hind limbs to the heart. Crocodilians & birds – some blood passing from hind limbs to the renal portal by-passes kidney capillaries, going straight through the kidneys to the postcava (see diagram above) Mammals – renal portal system not present in adults
Hepatic Portal system – similar in all vertebrates drains stomach, pancreas, intestine, & spleen & terminates in capillaries of liver
26. Describe the following veins:
Internal jugular – the deeper of the two jugular veins in the neck that drain blood from the head, brain, face and neck and convey it toward the heart. Arises from Anterior cardinal vein.
Brachiocephalic – either of a pair of veins in the neck, each formed by the union of the internal jugular and subclavian veins, that join to form the superior vena cava. From Common Cardinal V.
Azygous – one of a system of veins that drain the thoracic and abdominal walls arises as a continuation of the right ascending lumbar vein and terminates in the superior vena cava From Posterior Cardinal V.
Hemiazygous – a continuation of the left ascending lumbar vein crosses the midline at the 8th vertebra and empties into the azygos vein From Posterior Cardinal Vein.
Precavae/superior vena cava – carries blood from the head and arms and chest and empties into the right atrium of the heart formed from the azygos and both brachiocephalic veins. From Common Cardinal V.
Iliac – one of three veins draining the pelvic area
Subclavian – a part of a major vein of the upper extremities or forelimbs that passes beneath the clavicle and is continuous with the axillary vein
Umbilical – a vein that passes through the umbilical cord to the fetus and returns the oxygenated and nutrient blood from the placenta to the fetus
Ductus venosus – a fetal vein that passing through the liver to the inferior vena cava
Round ligament – a fibrous cord resulting from the obliteration of the umbilical vein of the fetus and passing from the navel to the notch in the anterior border of the liver and along the undersurface of that organ
Ligamentum venosum – a cord of tissue connected to the liver that is the vestige of the ductus venosus
Subintestinal – vein that drains the digestive system
Vitelline – any of the veins in a vertebrate embryo that return the blood from the yolk sac to the heart or later to the portal vein and in mammals have their function of bringing nutriment to the embryo superseded early by that of the umbilical vein
Inferior Vena Cava (postcava) – a large vein formed by the union of the two common iliac veins that receives blood from the lower limbs and the pelvic and abdominal viscera and empties into the right atrium of the heart. From Posterior Cardinal Vein.
27. Define portal and trunk as they relate to circulation.
Portal – vein that begins and ends in a capillary bed
Trunk – the main stem of a blood vessel apart from the branches-Subdivision of conus arteriosus. An Artery.
28. Trace the blood flow from the right atrium and back to the right atrium in a mammalian fetus.
The contents of the right atrium (which consist of some well oxygenated blood from the posterior vena cava and poorly oxygenated blood returning from the head and forelimbs via the anterior vena cava) enter the right ventricle and are expelled from the heart via the pulmonary artery. The lungs are bypassed by the ductus arteriosus, a shunt linking the pulmonary artery and the aorta, and the foramen ovale of the interatrial septum. The convergence of the poorly oxygenated pulmonary blood and the well-oxygenated aortic blood occurs after the main supply to the head and forelimbs have branched off the aortic arch. This ensures that the blood richest in oxygen reaches the developing brain. The abdominal aorta supplies the rest of the body and gives off two umbilical arteries (branches of the internal iliac arteries) which carry poorly oxygenated blood back to the placenta. The umbilical vein carries re-oxygenated fetal blood from the placenta back to the body cavity and to the liver. From the liver the oxygenated blood is carried through the ductus venosus to the posterior vena cava. Now oxygenated blood and deoxygenated blood are mixed and carried back to the right atrium.
Left Atrial Anatomy Relevant to Catheter Ablation
The rapid development of interventional procedures for the treatment of arrhythmias in humans, especially the use of catheter ablation techniques, has renewed interest in cardiac anatomy. Although the substrates of atrial fibrillation (AF), its initiation and maintenance, remain to be fully elucidated, catheter ablation in the left atrium (LA) has become a common therapeutic option for patients with this arrhythmia. Using ablation catheters, various isolation lines and focal targets are created, the majority of which are based on gross anatomical, electroanatomical, and myoarchitectual patterns of the left atrial wall. Our aim was therefore to review the gross morphological and architectural features of the LA and their relations to extracardiac structures. The latter have also become relevant because extracardiac complications of AF ablation can occur, due to injuries to the phrenic and vagal plexus nerves, adjacent coronary arteries, or the esophageal wall causing devastating consequences.
There continues to be a lack of understanding of the pathogenesis of AF. Current evidence suggests that the pathogenesis of AF is multifactorial, because this arrhythmia may not only accompany a variety of pathological conditions, but also occur in a heart with no known structural abnormality, a condition known as “lone AF” . Recent decades have seen rapid developments in arrhythmia treatment, especially with the use of catheter ablation approaches. These techniques in patients with AF have evolved from an initial simple approach focused on the pulmonary veins (PVs) and their junctions with the LA, to a more extensive intervention mainly, but not exclusively, targeting the left atrial myocardium . Because the LA is the main target of catheter ablation in patients with AF, in this review we examined the gross morphological and architectural features of this chamber and discussed the importance of its relations to neighboring extracardiac structures.
2. Components of the Left Atrium and Its Walls
From a gross anatomical viewpoint, the LA has four components : (1) a venous part that receives the PVs (2) a vestibule that conducts to the mitral valve (3) the left atrial appendage (LAA) and (4) the so-called interatrial septum (IAS). The body of LA is interposed between the vestibular and pulmonary venous components, with the PVs entering at the four corners of the venous part, enclosing a prominent atrial dome. The mean left atrial anteroposterior diameter is 38.4 ± 4.9 mm in normal subjects and will be increased with atrial fibrillation (range 44–74 mm). LA volume is larger in persistent AF (159.7 ± 57 mL) compared with paroxysmal AF (129.6 ± 44 mL) [4–6]. With atrial enlargement, the relative position distance of the esophagus to the left pulmonary veins may be increased but this is variable. The relative position of the left phrenic nerve to the left atrial appendage may change with LAA enlargement.
An anatomic septum in a heart is like a wall that separates adjacent chambers so that its removal would enable us to enter from one chamber to the other without exiting the heart. Thus, the true IAS wall is confined to the flap valve of the oval fossa. The flap valve is hinged from the muscular rim of IAS that, deriving from the septum secundum, is seen from the right atrial aspect of the interatrial wall . At its anteroinferior aspect, the muscular rim separates the oval fossa from the coronary sinus and the vestibule of the tricuspid valve (Figure 1). On the left atrial side of septum, there is no visible rim and the flap valve overlaps the oval rim quite considerably and two horns mark the usual site of fusion with the rim (Figure 1(c)). Therefore, we would like to emphasize that the true IAS is the oval fossa, a depression in the right atrial side of septum traditionally considered to be the IAS. The rest of muscular rim of the IAS is formed by the invagination of the right and left atrial myocardia that are separated by vascularized fibrofatty tissues of the extracardiac fat. This is why we prefer to use the term “interatrial groove” rather than muscular IAS, a concept that is very important during percutaneous interventions because transseptal punctures through the IAS to access the LA should be delimited to the boundary of the oval fossa. Thus, an inadvertent puncture throughout the interatrial groove (muscular IAS) may result in hemopericardium especially in a highly anticoagulated patient because blood will dissect the vascularized fibrofatty tissue that is sandwiched between the right and left atrial walls at this level . The location and size of the oval fossa varies from case to case, as does the profile or prominence of the muscular rim . The interatrial septum has a left ward angle of 45–60° relative to the horizontal plane. This orientation will be different and becomes more horizontal with right pneumonectomy, aortic aneurysm, or a large pleural effusion. Furthermore, abnormalities of the thorax or of the cardiovascular system such as kyphoscoliosis, marked left ventricular hypertrophy, or an enlarged aorta may result in displacement of the oval fossa .
) and the deep infolding of the atrial wall superior and inferior to the floor of the oval fossa (dotted lines). (b) Short axis section across the atrial chamber to show the thin flap valve (
) and the muscular rim of the oval fossa (arrow). Note the atrioventricular valves, the vestibule of the left atrium (dotted line), and the different shape and size of the atrial appendages. (c) and (d) Longitudinal sections through the pulmonary venous component showing the orifices of the right and left PVs and the ostium of the left atrial appendage the flap valve of the oval fossa overlaps (
) the rim to form the septal aspect of the left atrium. (e) A magnification of the left aspect of the interatrial septum. Note that, apart from a small crescent-like edge (arrows), the left atrial side of the septum can be seen by transillumination of the oval fossa (
) in the right side. In the case of patent foramen oval, the LA can be accessed from the right atrium (RA) through a crevice (
The major part of the endocardial LA including the septal wall and interatrial groove component is relatively smooth. The left aspect of the interatrial groove, apart from a small crescent-like edge (Figure 1(e)), is almost indistinguishable from the parietal atrial wall. The smoothest parts are the superior and posterior walls, which make up the pulmonary venous component and the vestibule surrounding the mitral orifice. Behind the posterior wall of the vestibular component of the LA is the anterior wall of the coronary sinus  (Figures 1(c) and 1(d)).
The walls of LA are nonuniform in thickness (Figure 1(f)) and in general appear thicker than the right atrium. The walls can be described as being anterior, superior, left lateral, septal, and posterior. The anterior wall is located behind the ascending aorta and the transverse pericardial sinus. The anterior wall thickness measures 3.3 ± 1.2 mm in unselected postmortem hearts . Part of the anterior wall immediately inferior to the Bachmann bundle and posterior to the aorta can be very thin (1-2 mm). The roof or the superior wall is in close proximity to the right pulmonary artery with a mean thickness of 4.5 ± 0.6 mm. The lateral wall thickness is 3.9 ± 0.7 mm. In normal hearts, the anteroinferior rim of the IAS measures 5.5 ± 2.3 mm and the flap valve measures 1.5 ± 0.6 mm . The posterior wall thickness is greatest inferiorly, at 6.5 ± 2.5 mm, when measured immediately superior to the coronary sinus and between 6 and 15 mm from the mitral annulus. By contrast, it is thinnest, at 2.2 ± 0.3 mm, at the right or left venoatrial junctions . In some samples of histological sections obtained at the PV and posterior atrial wall, small areas of discontinuities are seen in the myocardial layer replaced with fibrous tissue.
3. The Myoarchitecture of the Left Atrium
Detailed dissections of the subendocardial and subepicardial myofibers along the entire thickness of the LA walls have shown a complex architecture of overlapping bands of aligned myocardial bundles [12, 13] (Figure 2). The term “fibers” describes the macroscopic appearance of strands of cardiomyocytes. These fibers are circumferential when they run parallel to the mitral annulus and longitudinal when they are approximately perpendicular to the mitral orifice.
Although there are some individual variations, our epicardial dissections of the LA have shown a distinctive pattern of arrangement of the myocardial fibers . On the subepicardial aspect of LA, the fibers in the anterior wall consisted of a main bundle that ran parallel to the atrioventricular groove. This was the continuation of the interatrial bundle (Bachmann bundle) [12, 13], which could be traced rightward to the junction between the right atrium and the superior caval vein (Figures 2(a) and 2(b)). In the LA, the interatrial bundle was joined inferiorly at the septal raphe (the portion that is buried in the atrial septum) by fibers arising from the anterior rim of the oval fossa. Superiorly, it blended with a broad band of circumferential fibers that arose from the anterosuperior part of the septal raphe to sweep leftward into the lateral wall. Reinforced superficially by the interatrial bundle, these circumferential fibers passed to either side of the neck of the atrial appendage to encircle the appendage and reunited as a broad circumferential band around the inferior part of the posterior wall to enter the posterior septal raphe.
The epicardial fibers of the superior wall are composed of longitudinal or oblique fibers, (named by Papez as the “septopulmonary bundle” in 1920)  (Figures 2(a), 2(b), and 2(c)) that arise from the anterosuperior septal raphe, beneath the circumferential fibers of the Bachmann bundle. As they ascend the roof, they fan out to pass in front of, between, and behind the right and left PVs and the myocardial sleeves that surround the venous orifices. On the posterior wall, the septopulmonary bundle often bifurcates to become two oblique branches. The leftward branch fused with, and was indistinguishable from, the circumferential fibers of the anterior and lateral walls, whereas the rightward branch turned into the posterior septal raphe.
On the subendocardial aspect of LA, most specimens showed a common pattern of general architecture. The dominant fibers in the anterior wall were those originating from a bundle described by Papez as the septoatrial bundle . The fibers of this bundle ascended obliquely from the anterior interatrial raphe and combined with longitudinal fibers arising from the vestibule. They passed the posterior aspect of the LA between the left and right pulmonary veins, blending with longitudinal or oblique fibers of the septopulmonary bundle from the subepicardial layer. The septoatrial bundle also passed leftward, superior, and inferior to the mouth of the LAA to reach the lateral and posterior walls. Some of these fibers encircled the mouth of the LAA and continued into the pectinate muscles within the appendage.
Atrial fibrillation is the most common sustained cardiac arrhythmia and is characterized by uncoordinated contraction of the atrium. It is still unclear whether the initiation and maintenance of human AF depends on automatic focal or reentrant mechanisms. Recent reports have shown the contribution of different atrial regions on the fibrillatory process and to the maintenance of AF, emphasizing the role of structural discontinuities and heterogeneous fiber orientation favoring anatomic reentry or anchoring rotors [15, 16]. The posterior wall of the LA, for example, seems to play an important role in maintaining AF. Morillo et al.  reported in a canine model of AF that cryoablation at sites of short cycle length activity in the posterior LA resulted in the interruption of this arrhythmia. Observations from the laboratory of Jalife and coworkers  demonstrated in the isolated sheep heart the presence of a small number of stable ongoing circuits generating high frequency waves and providing a base to generate fibrillatory conduction. Data derived from high resolution optical mapping and histological sections in this animal model also showed that the focal sources correspond to single or a small number of reentrant rotors discharging at a high frequency and that these are localized in the PV orifices or at the contiguous posterior left atrial region . Postmortem examination in human specimens showed in most hearts an abrupt change of subendocardial fiber orientation (circumferential, oblique, and longitudinal) in the posterior wall of the LA (Figure 2(c)) at the venoatrial junctions. In these areas, the subendocardial fibers are usually loop-like extensions from the longitudinal fibers encircling the venoatrial junctions [12, 13]. The finding of changes in myoarchitecture transmurally is also relevant. The most obvious broad band or linear anatomic barrier of longitudinal and oblique fibers was formed by the septopulmonary bundle that also marked a change in LA wall thickness. Left atrial endocardial activation was mapped in 19 patients with a percutaneous noncontact mapping system during episodes of focal initiation of AF . In this study, Markides et al.  observed that the pattern of LA activation was predominantly determined by a principal line of conduction block. It appears to be related to the linear anatomic barrier identified by the examination of fiber orientation at the level of the septopulmonary bundle.
4. Pulmonary Veins and the Atrial Fibrillation Ablation
Although different mechanisms of AF exist, it is well established that the myocardial sleeves of the PVs, especially the superior veins, are crucial sources of triggers that initiate AF . Cardiac ablation is performed in symptomatic AF. Furthermore, patients with larger LA size and longer AF duration typically experience a higher incidence of AF recurrence . Previously, the most common ablation strategy was electrical isolation of the PVs by creating circumferential ablation lines around the individual or bilateral PV ostia . However, the focus of ablation strategies shifted from the PV ostium to the atrial tissue located in the venoatrial junctions due to the fact that many non-PV trigger points for AF are located in the venoatrial junctions rather than the PV and that radiofrequency catheter ablation (RFCA) techniques may cause PV stenosis .
Normal PVs anatomy consists of two right-sided and two left-sided PVs with separate ostia (Figures 2 and 3). However, in anatomical studies with multidetector CT (MDCT) it has been demonstrated that the anatomy of the LA and PVs is commonly variable . The PV ostia are ellipsoid with a longer superior-inferior dimension. The right superior PV is located close to the superior vena cava and the right inferior PV possesses a projection horizontally. The left superior PV is close to the LAA and the left inferior PV courses near the descending aorta. The veins are larger in AF versus non-AF patients, men versus women, and persistent versus paroxysmal patterns. The PV trunk is defined as the distance from the ostium to the first-order branch. The superior PV ostia are larger (19-20 mm) than the inferior PV ostia (16-17 mm) . The superior PVs tend to have a longer trunk (21.6 ± 7.5 mm) than the inferior PVs (14.0 ± 6.2 mm) . It is important to measure the ostial diameters of each vein and the length to the first-order branch. These diameters influence the selection of the circular catheter size used. Common anomalies include a conjoined (common) left or right pulmonary vein in 25% of individuals . A conjoined PV is seen more frequently on the left than the right side . Supernumerary veins are also frequent. The most common is a separate right middle PV, which drains the middle lobe of the lung  (Figure 4). One or two middle lobe vein ostia can be seen in 26% of patients . The ostial diameter of the right middle PV is smaller than that of the other veins (mean, 9.9 ± 1.9 mm). In some patients, there is a supernumerary PV that shows an aberrant insertion, with a perpendicular position in relation to the LA posterior wall. The supernumerary branch usually drains the upper lobe of the right lung and characteristically passes behind the bronchus intermedius. The absence of one PV requires careful examination of the whole intrathoracic venous system since it may be associated with partial anomalous venous return (Figure 5). The caliber of the PVs gradually increases as they approach the LA. However, the caliber of the left inferior PV may decrease as it enters the LA.
Heart Limits: The anterior surface is just below the sternum and ribs. The inferior surface is the part of the heart that mostly rests on the diaphragm, corresponding to the region between the apex and the right approach. The right border is toward the right lung and extends from the bottom surface to the base The left border, also called the pulmonary border, faces the left lung, extending from the base to the apex. The upper limit is the great vessels of the heart and later the trachea, esophagus and descending aorta.
| HEART LIMITS |
Cardiac Wall Layers:
Pericardium: the membrane that covers and protects the heart. It restricts the heart to its position in the mediastinum, yet allows sufficient freedom of movement for vigorous and rapid contractions. The pericardium consists of two main parts: fibrous pericardium and serous pericardium.
The superficial fibrous pericardium It is an irregular, dense, resistant and inelastic connective tissue. It resembles a sac, which rests on and attaches to the diaphragm.
The serous pericardiumDeeper is a thinner and more delicate membrane that forms a double layer, surrounding the heart. The outermost parietal layer of the serous pericardium is fused to the fibrous pericardium. The innermost visceral layer of the serous pericardium, also called the epicardium, adheres strongly to the surface of the heart.
| PERICARDIAL BAG |
Myocardium: is the middle and thickest layer of the heart. It is composed of striated cardiac muscle. It is this type of muscle that allows the heart to contract and therefore to thrust blood, or force it into the blood vessels.
Endocardium: is the innermost layer of the heart. It is a thin layer of tissue made up of simple squamous epithelium over a layer of connective tissue. The smooth and shiny surface allows blood to flow easily over it. The endocardium also coats the valves and is continuous with the lining of blood vessels entering and leaving the heart.
The heart has three faces and four margins:
- Anterior Face (Sternocostal) & #8211 Formed mainly by the right ventricle.
- Diaphragmatic Face (Lower) & #8211 Formed mainly by the left ventricle and partially by the right ventricle It is mainly related to the central tendon of the diaphragm.
- Lung Face (Left) & #8211 Formed mainly by the left ventricle It occupies the cardiac impression of the left lung.
- Right bank & #8211 Formed by the right atrium and extending between the superior and inferior vena cavae.
- Lower Margin & #8211 Formed mainly by the right ventricle and slightly by the left ventricle.
- Left margin & #8211 Formed mainly by the left ventricle and slightly by the left atrium.
- Top margin & #8211 Formed by the right and left atria and atria in an anterior view the ascending part of the aorta and the pulmonary trunk emerge from the superior margin, and the superior vena cava enters its right side. Posterior to the aorta and pulmonary trunk and anterior to the superior vena cava, the upper margin forms the lower limit of the transverse sinus of the pericardium.
Externally the atrioventricular ostia correspond to the coronary sulcus, which is occupied by coronary arteries and veins, this sulcus surrounds the heart and is interrupted anteriorly by the aorta and pulmonary trunk.
The interventricular septum on the anterior surface corresponds to the anterior interventricular sulcus and on the diaphragmatic face to the posterior interventricular sulcus.
The interventricular sulcus ends less than a few centimeters from the right of the apex of the heart, corresponding to the notch of the apex of the heart.
The anterior interventricular sulcus is occupied by the anterior interventricular vessels.
This groove is occupied by the posterior interventricular vessels.
The posterior interventricular sulcus starts from the coronary sulcus and descends toward the notch of the apex of the heart.
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The heart has four chambers: two atria and two ventricles. The Atriums (the upper chambers) receive blood the Ventricles (lower chambers) pump blood out of the heart
On the front of each atrium is a wrinkled, sac-shaped structure called the auricle (similar to a dog's ear).
The right atrium is separated from the left by a thin partition called the interatrial septum the right ventricle is separated from the left by the interventricular septum.
| INTERNAL HEART CONFIGURATION |
|Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.|
The right atrium forms the right edge of the heart and receives blood rich in carbon dioxide (venous) from three veins: superior vena cava, inferior vena cava and coronary sinus.
The superior vena cava collects blood from the head and upper body, the lower one receives blood from the lower parts of the body (abdomen and lower limbs) and the coronary sinus receives the blood that nourished the myocardium and takes the blood to the right atrium. .
While the posterior wall of the right atrium is smooth, the anterior wall is rough due to the presence of muscle ridges, called pectinate muscles.
Blood passes from the right atrium to the right ventricle through a valve called the tricuspid (formed by three leaflets & #8211 valves or cusps).
In the medial wall of the right atrium, which consists of the interatrial septum, we find a depression that is the fossa ovalis.
Formerly, the right atrium has a pyramidal expansion called the right atrium, which serves to dampen the impulse of blood as it enters the atrium.
The holes where the vena cavae open have the names of ostia of the vena cavae.
The opening of the coronary sinus is called the coronary sinus ostium and we also find a slide that prevents blood from returning from the atrium to the coronary sinus which is called the coronary sinus valve.
The left atrium is a thin-walled cavity with smooth posterior and anterior walls that receives the already oxygenated blood through four pulmonary veins. Blood passes from the left atrium to the left ventricle through the Bicuspid valve (mitral), which has only two cusps.
The left atrium also has a pyramidal expansion called the left atrium.
The right ventricle forms most of the anterior surface of the heart. Its interior has a series of high bundles of cardiac muscle fibers called fleshy trabeculae.
In the right atrioventricular ostium there is a device called Tricuspid valve which prevents blood from returning from the ventricle to the right atrium. This valve consists of three whitish and irregularly triangular membrane blades, with the base implanted at the edges of the ostium and the apex directed downward and attached to the ventricle walls by filaments.
Each blade is called a cusp. We have an anterior, another posterior, and another septal cusp.
The apex of the cusps is trapped by filaments called Tendon Ropes, which fall into small fleshy columns called Papillary muscles.
The pulmonary trunk valve is also made up of small blades, but these are arranged in a shell, called semilunar valves (anterior, left and right).
In the center of the free border of each of the valves we find small nodules called semilunar (pulmonary) valve nodules.
The left ventricle forms the apex of the heart. In the left atrioventricular ostium, we find the left atrioventricular valve, consisting only of two laminae called cusps (anterior and posterior). These valves are called bicuspids. Like the right ventricle, it also has fleshy trabeculae and tendon cords that attach the bicuspid valve cusps to the papillary muscles.
Blood passes from the left atrium to the left ventricle through the left atrioventricular ostium where the Bicuspid valve (mitral). From the left ventricle, blood exits to the largest artery in the body, the ascending aorta, through the Aortic valve & #8211 consisting of three semilunar valves: right, left and posterior. Hence, part of the blood flows to the coronary arteries, which branch from the ascending aorta, bringing blood to the heart wall the remaining blood passes to the aortic arch and descending aorta (thoracic aorta and abdominal aorta). Branches of the aortic arch and descending aorta carry blood throughout the body.
The left ventricle receives oxygenated blood from the left atrium. The main function of the left ventricle is to pump blood to the systemic circulation (body). The left ventricular wall is thicker than that of the right ventricle. This difference is due to the greater force required to pump blood into the systemic circulation.
| LARGE HEART VESSELS |
|Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.|
A single heart cycle includes all events associated with a heartbeat. In the normal cardiac cycle the two atria contract, while the two ventricles relax and vice versa. The term systole designates the contraction phase The relaxation phase is called diastole.
When the heart beats, the atria contract first (atrial systole), forcing blood to the ventricles. Once filled, the two ventricles contract (ventricular systole) and force the blood out of the heart.
|Valves in Ventricular Diastole||Valve Dynamism||Valves in Ventricular Systole|
For the heart to be efficient in its pumping action, it takes more than the rhythmic contraction of its muscle fibers. The direction of blood flow should be oriented and controlled, which is obtained by four valves previously mentioned: two located between the atrium and the ventricle & #8211 atrioventricular (tricuspid and bicuspid valve) and two located between the ventricles and the large arteries that carry blood out of the heart & #8211 semilunar (pulmonary and aortic valve) .Complement: The valves and valves are to prevent this abnormal blood behavior, to prevent reflux from occurring, they close after the blood has passed.
Systole It is the contraction of the heart muscle, we have atrial systole that pushes blood to the ventricles. Thus the atrioventricular valves are open to blood flow and the pulmonary and aortic valves are closed. In ventricular systole, the atrioventricular valves are closed and the semilunar valves open to the passage of blood.
| VENTRICULAR SYMPTOM & #8211 ACTION OF Atrio-Ventricular Valves |
|Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.|
| VENTRICULAR DIASTOLE & #8211 ACTION OF Atrio-Ventricular Valves |
|Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.|
In conclusion we can say that the cardiac cycle comprises:
1- Atrial systole
2- Ventricular systole
3- Ventricular Diastole
The heart is irrigated by the coronary arteries and the coronary sinus.
The coronary arteries are two, one right and one left. They have this name because both run through the coronary sulcus and are both originating from the aortas artery.
Immediately after its origin, the artery goes to the coronary sulcus running from right to left until it anastomoses with the circumflex branch, which is the terminal branch of the left coronary artery that continues the sulcus. coronary.
The Right Coronary Artery: from the origin to two arteries that will irrigate the right margin and the posterior part of the heart, they are right marginal artery and posterior interventricular artery.
The Left Coronary ArteryInitially, it passes through a branch behind the pulmonary trunk to reach the coronary sulcus, showing itself near the apex of the left atrium.
Immediately after, it emits an anterior interventricular branch and a circumflex branch that originates the left marginal artery.
On the diaphragmatic face the two arteries anastomose to form a circumflex branch.
Venous blood is collected from several veins that flow into the great heart vein, which starts at the apex of the heart, rises the anterior interventricular sulcus and follows the left-to-right coronary sulcus through the diaphragmatic face to flow into the atrium. right.
The terminal portion of this vessel, represented by its last 3 cm, forms a dilation that is named coronary sinus.
The coronary sinus also receives the middle heart vein, which runs from the bottom up the posterior interventricular sulcus and the small heart vein that borders the right edge of the heart.
There are still very small minimal veins that flow directly into the cardiac cavities.
The innervation of the heart muscle is in two ways: extrinsic from nerves outside the heart and intrinsic from a system found only in the heart and located within.
Extrinsic innervation derives from the autonomic nervous system, that is, sympathetic and parasympathetic.
From the sympathetic, the heart receives the sympathetic cardiac nerves, being three cervical and four or five thoracic.
The parasympathetic fibers going to the heart follow the vagus nerve (X cranial nerve), from which parasympathetic cardiac nerves are derived, two cervical and one thoracic.
Physiologically the sympathetic accelerates and the parasympathetic slows down the heartbeat.
The intrinsic innervation or conduction system of the heart is the reason for the continuous heartbeat. It is an intrinsic, rhythmic electrical activity that originates in a network of specialized cardiac muscle fibers called auto-rhythmic cells (cardiac pacemakers) because they are self-exciting.
Cardiac excitation begins at the sinoatrial node (SA), located in the right atrial wall, inferior to the opening of the superior vena cava. Propagating along the atrial muscle fibers, the action potential reaches the atrioventricular (AV) node, located in the interatrial septum, anterior to the opening of the coronary sinus. From the AV node, the action potential reaches the atrioventricular bundle (His bundle), which is the only electrical connection between the atria and the ventricles. After being conducted along the AV bundle, the action potential enters the right and left branches, which cross the interventricular septum, towards the cardiac apex. Finally, conductive myofibers (Purkinge fibers) rapidly conduct the action potential, first to the apex of the ventricle and then to the rest of the ventricular myocardium.
| HEART ELECTRICAL SYSTEM |
|Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.|
Diastole is the relaxation of the heart muscle, when the ventricles are filled with blood, at this time the atrioventricular valves are open and the semilunar valves are closed.
The right atrium (RA) forms the rightward and anterior part of the cardiac mass. This overlaps the right band margin of the left atrium (LA). The leftward margin of the RA is marked posteriorly by the interatrial groove, which lies between the superior caval vein and the right pulmonary veins. Owing to the obliquity of the interatrial septum (IAS) plane (approximately 65° from the sagittal plane), and to the different levels of the mitral and tricuspid valve orifices, the left atrium is turned and situated posterior and superior to the right atrium. Only the tip of the LAA contributes to the left cardiac silhouette in a frontal fluoroscopic view of the body (figure 1).
Spatial relationship of the atrial structures as they lie in the body. Posterior, right lateral, and superior view of volume rendered CT angiographies are shown. The left atrium (LA in red) is located superior and posterior to the right atrium. Its superior (S) and posterior (P) walls are shown by double-headed arrows. The right atrial appendage (RAA) is shown in yellow and the venous component of the right atrium in blue. The coronary sinus (CS) tributaries are shown in green. IVC, inferior vena cava LAA, left atrial …
Other Cardiac Structures
The cardiac imaging planes routinely used in cardiac nuclear medicine, MR imaging, and echocardiography are easily created at a 3D workstation using the acquired cardiac CT angiographic data. Evaluation of MPR images in combination with use of these routine cardiac imaging planes allows comprehensive evaluation of cardiac anatomy and function.
Cardiac Imaging Planes and the Left Side of the Heart
Vertical Long-Axis View.—
The vertical long-axis view is a parasagittal plane oriented along the long axis of the LV lumen. The relationship between the left atrium (LA) and the LV is assessed on vertical long-axis images ( , Fig 10). The inferior and anterior walls of the LV myocardium are optimized on this view. The structure and function of the bicuspid MV and LV are well demonstrated on vertical long-axis cine images, and the LA appendage and CS are routinely depicted ( , Fig 10).
Horizontal Long-Axis View.—
The horizontal long-axis view, or four-chamber view, is a horizontal plane through the heart that essentially bisects all four cardiac chambers ( , Fig 11). The resultant display readily allows assessment of chamber size and valve position. The septal, apical, and lateral LV walls can be simultaneously assessed. The lateral wall of the LV is normally thin at the apex (typically 1–2 mm), even in abnormally thickened hearts ( , 13). Subjective evaluation of AV valvular and ventricular function is usually also possible in cine mode.
Because most workstations can quickly calculate the area of a structure specified by the user, LA size can readily be determined. A line is drawn along the endocardial border of the LA at the level of the MV on the horizontal long-axis view ( , Fig 12). This line creates an irregular ellipse, exclusive of the pulmonary veins (PVs) and LA appendage. The area of the ellipse is automatically calculated by the workstation. An area of less than 20 cm 2 is normal, 20–30 cm 2 is mildly abnormal, 30–40 cm 2 is moderately abnormal, and greater than 40 cm 2 is severely abnormal ( , 14).
The three-chamber view is an oblique long-axis view that optimizes visualization of the LV, LA, aortic root, MV, and aortic valve ( , Fig 13). It is usually obtained manually, with a plane oriented through the aortic root, aortic valve, MV, and LV on a short-axis view obtained at the base of the heart. The three-chamber view allows evaluation of the LV outflow tract, aortic valve, aortic root, and proximal ascending thoracic aorta. The posteromedial papillary muscles are often seen arising from the LV free (lateral) wall on this view. These muscles are connected to the MV by chordae tendineae, which are linear fibrous bands. During systole, the LV myocardium contracts. The papillary muscles likewise contract, tugging on the MV leaflets to ensure complete closure of the MV and prevent regurgitation ( , Fig 14).
The short-axis view is obtained in an oblique coronal plane relative to the thorax, down the barrel of the LV lumen ( , Fig 15). As one progresses from the MV toward the apex in the short axis, the basal, middle, and apical portions of the LV myocardium can be evaluated. This plane allows easy assessment of LV size and myocardial contractility.
Right Side of the Heart
Depending on the injection protocol used, varying levels of enhancement of the right side of the heart are achieved. If this side of the heart is enhanced with contrast material, the RA, RV, and tricuspid valves can be assessed in detail. The RA receives inflow primarily from the superior vena cava and inferior vena cava, as well as from the CS. The crista terminalis is located at the RA–superior vena cava junction and is a muscular ridge that separates the smooth muscle fibers of the posterior RA from trabeculated muscle fibers anteriorly. The eustachian valve is located at the RA–inferior vena cava junction and directs flow toward the foramen ovale ( , Fig 16) ( , 7). The thebesian valve prevents reflux from the RA into the CS ( , Fig 17) ( , 15).
The RV is the most anterior of the cardiac chambers and has a heavily trabeculated apex and papillary muscles whose functions are similar to those of the LV papillary muscles. The smooth, muscular infundibulum (or conus) of the RV is the outflow portion of the RV directly inferior to the pulmonary valve ( , Fig 18 , ). A characteristic feature of the RV is the moderator band, a muscular band extending from the interventricular septum to the base of the anterior papillary muscle. The moderator band is part of the right bundle branch conduction system ( , Fig 19). Although the moderator band and the heavily trabeculated apex are distinct features of the RV, other features such as a well-developed infundibulum, septal papillary muscles, and lack of fibrous continuity of the AV valve and outflow tract are key to differentiating the RV from the LV ( , 16). In complex cases of congenital heart disease, the ability to distinguish the LV from the RV may be of paramount importance.
Evaluation of the RV can be performed with any multidetector CT study of the thorax and provides significant prognostic information relative to the diagnosis of acute pulmonary embolism. Comparing the size of the RV to that of the LV (RV/LV diameter ratio) on axial images has been shown to correlate with the severity of pulmonary embolism and fatal outcome ( , 17). The RV measurement is obtained at the level of the tricuspid valve and represents the maximum distance between the endocardial surface of the free wall and the endocardial surface of the septal wall. A similar measurement of the LV is obtained at the level of the MV, and the RV/LV diameter ratio is calculated. A ratio of 1 or less is normal, whereas a ratio greater than 1.5 indicates severe pulmonary embolism ( , 17).
Cardiac and Pulmonary Veins
Cardiac CT angiography is excellent for imaging the CS and cardiac veins ( , Fig 20 , ). The components of the cardiac venous system are variable, but the most constant structure is the CS itself, which runs along the inferior aspect of the heart in the AV groove before emptying into the RA ( , 7, , 18). The first branch of the CS is the posterior interventricular vein, also known as the middle cardiac vein, which courses in the posterior interventricular groove from base to apex ( , 18). The next two branches are the posterior vein of the LV and the left marginal vein. At this point, the CS becomes the great cardiac vein, which courses in the left AV groove with the LCx artery. It then continues as the anterior interventricular vein in the anterior interventricular groove, coursing from the base of the heart toward the apex adjacent to the LAD artery.
Variability in the cardiac veins is usually due to absence of either the left marginal vein or the posterior vein of the LV ( , 19). Only approximately 55% of patients have the latter vein, with 83% having a left marginal vein ( , 19, , 20). Knowledge of this variability is important for the outpatient work-up of patients prior to cardiac resynchronization therapy, which is often performed with cardiac CT angiography. Patients treated with cardiac resynchronization therapy typically undergo implantation of an automatic cardioverter-defibrillator for the treatment of heart failure, ideally with a transvenous approach. During this procedure, the LV pacer lead is most commonly inserted into either the posterior vein of the LV or the left marginal vein ( , 18, , 19). After cardiac CT angiography, if no suitable vein is present in which to place the LV pacer lead with a transvenous approach, surgical placement may be necessary ( , 19).
The PVs have received significant attention recently. LA muscle can extend into the venous ostia, and ectopic electrical foci originating at this site may be the cause of atrial fibrillation in a significant number of patients ( , 21). The veins can be mapped in detail with multidetector CT, and treatment strategies that make use of radiofrequency catheter ablation performed on the basis of CT findings can be tailored to individual patients ( , 21). Typically, two veins (superior and inferior) drain into either side of the LA ( , Fig 21). If additional PVs are present, it is important that they be described prior to ablation. They are typically single and occur more commonly on the right side ( , 21). In particular, middle PVs arising on the right side have a stronger association with atrial fibrillation ( , 21).
Patients with atrial fibrillation may develop thrombus in the LA appendage, a condition that can be evaluated with multidetector CT prior to PV ablation. In most adults (>97%), the LA appendages have pectinate muscles measuring greater than 1 mm ( , 22). These muscles are continuous fibers running parallel to each other within the LA appendage and should not be mistaken for thrombus in contrast, clot manifests as a focal filling defect. The RA appendage also has pectinate muscles ( , 7), although they are slightly larger than those of the LA appendage.
The LA appendage arises from the superolateral aspect of the LA and projects anteriorly over the proximal LCx artery. It is more tubular than the normally pyramidal RA appendage and has a narrower base ( , 7). These features readily allow differentiation between the two appendages ( , Fig 22 , , ), which can be useful when situs is questioned.
The four cardiac valves are routinely imaged during cardiac CT angiography, and their motion and morphologic characteristics should also be assessed at all cardiac CT angiographic examinations with reconstructed and cine images.
The MV separates the LA from the LV. It is normally connected to the morphologic LV ( , Figs 10, , 11). The MV is composed of two leaflets, the anterior and posterior leaflets the other valves normally have three leaflets. The MV and aortic valve share fibrous continuity. The MV annulus, or valve ring, is part of the cardiac skeleton and is imbedded in the myocardium ( , 7). Normally, the boundaries of the MV annulus are not readily apparent at cardiac CT angiography. However, calcification of the MV annulus is a common abnormality that makes identification of the annulus possible at cardiac CT angiography. The papillary muscles (described earlier) with their chordae tendineae are also a component of the MV apparatus.
The tricuspid valve separates the RA from the RV ( , Fig 11) and is composed of the same structures as the MV: leaflets, annulus, commissures (sites where two leaflets come together to attach to the aortic wall), papillary muscles, and chordae tendineae. It is normally connected to the morphologic RV. As its name implies, the tricuspid valve is a trileaflet valve (anterior, posterior, and septal leaflets) and is separated from the pulmonary valve by the crista supraventricularis—a muscular ridge—unlike the MV, which is contiguous with the aortic valve ( , 7).
The aortic valve separates the LV outflow tract from the ascending aorta. It is composed of an annulus, cusps, and commissures. No papillary muscles or chordae tendineae are associated with the aortic valve. The three cusps (right, left, and posterior or noncoronary) of the aortic valve form pocketlike outpouchings that are designed to direct blood into the sinuses of Valsalva during diastole ( , Fig 23) ( , 7).
The pulmonary valve separates the RV outflow tract from the main pulmonary artery but does not connect directly to the tricuspid valve ( , Fig 18a , ). It is otherwise essentially identical to the aortic valve, with right, left, and posterior leaflets.
The pericardium is normally paper thin, measuring 2 mm or less ( , Fig 11). It is composed of two layers, the parietal layer and the serous layer. The tough outer parietal layer envelops the heart and attaches to the sternum and proximal great vessels in fact, most of the ascending aorta and main pulmonary artery, portions of the venae cavae, and most of the PVs are intrapericardial ( , 7). The inner, more delicate serous layer lines both the fibrous pericardium and the outer surface of the heart and great vessels ( , 7). The pericardium lining the surface of the heart is known as the visceral pericardium, or epicardium. Multidetector CT routinely depicts the fluid-filled junctions of the visceral and parietal pericardia, which form recesses and sinuses ( , 23). The oblique and transverse sinuses are two of the most commonly encountered sinuses at multidetector CT of the heart and thorax ( , Fig 24) and are continuous with the pericardial cavity ( , 23). It is important to be aware of the more common recesses and sinuses to distinguish them from lymphadenopathy or abnormal soft tissue ( , 23).
Structure separating the left atrium from the ascending aorta? - Biology
albumin most abundant plasma protein, accounting for most of the osmotic pressure of plasma
anastomosis (plural = anastomoses) area where vessels unite to allow blood to circulate even if there may be partial blockage in another branch
anterior cardiac veins vessels that parallel the small cardiac arteries and drain the anterior surface of the right ventricle bypass the coronary sinus and drain directly into the right atrium
anterior interventricular artery (also, left anterior descending artery or LAD) major branch of the left coronary artery that follows the anterior interventricular sulcus
anterior interventricular sulcus sulcus located between the left and right ventricles on the anterior surface of the heart
antibodies (also, immunoglobulins or gamma globulins) antigen-specific proteins produced by specialized B lymphocytes that protect the body by binding to foreign objects such as bacteria and viruses
aortic valve (also, aortic semilunar valve) valve located at the base of the aorta
arteriole (also, resistance vessel) very small artery that leads to a capillary
arteriovenous anastomosis short vessel connecting an arteriole directly to a venule and bypassing the capillary beds
artery blood vessel that conducts blood away from the heart may be a conducting or distributing vessel
atrioventricular septum cardiac septum located between the atria and ventricles atrioventricular valves are located here
atrioventricular valves one-way valves located between the atria and ventricles the valve on the right is called the tricuspid valve, and the one on the left is the mitral or bicuspid valve
atrium (plural = atria) upper or receiving chamber of the heart that pumps blood into the lower chambers just prior to their contraction the right atrium receives blood from the systemic circuit that flows into the right ventricle the left atrium receives blood from the pulmonary circuit that flows into the left ventricle
auricle extension of an atrium visible on the superior surface of the heart
bicuspid valve (also, mitral valve or left atrioventricular valve) valve located between the left atrium and ventricle consists of two flaps of tissue
blood liquid connective tissue composed of formed elements—erythrocytes, leukocytes, and platelets—and a fluid extracellular matrix called plasma component of the cardiovascular system
buffy coat thin, pale layer of leukocytes and platelets that separates the erythrocytes from the plasma in a sample of centrifuged blood
capacitance ability of a vein to distend and store blood
capacitance vessels veins
capillary smallest of blood vessels where physical exchange occurs between the blood and tissue cells surrounded by interstitial fluid
capillary bed network of 10–100 capillaries connecting arterioles to venules
cardiac notch depression in the medial surface of the inferior lobe of the left lung where the apex of the heart is located
cardiac skeleton (also, skeleton of the heart) reinforced connective tissue located within the atrioventricular septum includes four rings that surround the openings between the atria and ventricles, and the openings to the pulmonary trunk and aorta the point of attachment for the heart valves
cardiomyocyte muscle cell of the heart
chordae tendineae string-like extensions of tough connective tissue that extend from the flaps of the atrioventricular valves to the papillary muscles
continuous capillary most common type of capillary, found in virtually all tissues except epithelia and cartilage contains very small gaps in the endothelial lining that permit exchange
coronary arteries branches of the ascending aorta that supply blood to the heart the left coronary artery feeds the left side of the heart, the left atrium and ventricle, and the interventricular septum the right coronary artery feeds the right atrium, portions of both ventricles, and the heart conduction system
coronary sinus large, thin-walled vein on the posterior surface of the heart that lies within the atrioventricular sulcus and drains the heart myocardium directly into the right atrium
coronary sulcus sulcus that marks the boundary between the atria and ventricles
coronary veins vessels that drain the heart and generally parallel the large surface arteries
elastic artery (also, conducting artery) artery with abundant elastic fibers located closer to the heart, which maintains the pressure gradient and conducts blood to smaller branches
endocardium innermost layer of the heart lining the heart chambers and heart valves composed of endothelium reinforced with a thin layer of connective tissue that binds to the myocardium
endothelium layer of smooth, simple squamous epithelium that lines the endocardium and blood vessels
epicardial coronary arteries surface arteries of the heart that generally follow the sulci
epicardium innermost layer of the serous pericardium and the outermost layer of the heart wall
external elastic membrane membrane composed of elastic fibers that separates the tunica media from the tunica externa seen in larger arteries
fenestrated capillary type of capillary with pores or fenestrations in the endothelium that allow for rapid passage of certain small materials
fibrinogen plasma protein produced in the liver and involved in blood clotting
foramen ovale opening in the fetal heart that allows blood to flow directly from the right atrium to the left atrium, bypassing the fetal pulmonary circuit
formed elements cellular components of blood that is, erythrocytes, leukocytes, and platelets
fossa ovalis oval-shaped depression in the interatrial septum that marks the former location of the foramen ovale
globulins heterogeneous group of plasma proteins that includes transport proteins, clotting factors, immune proteins, and others
great cardiac vein vessel that follows the interventricular sulcus on the anterior surface of the heart and flows along the coronary sulcus into the coronary sinus on the posterior surface parallels the anterior interventricular artery and drains the areas supplied by this vessel
hematocrit (also, packed cell volume) volume percentage of erythrocytes in a sample of centrifuged blood
hypertrophic cardiomyopathy pathological enlargement of the heart, generally for no known reason
immunoglobulins (also, antibodies or gamma globulins) antigen-specific proteins produced by specialized B lymphocytes that protect the body by binding to foreign objects such as bacteria and viruses
inferior vena cava large systemic vein that returns blood to the heart from the inferior portion of the body
interatrial septum cardiac septum located between the two atria contains the fossa ovalis after birth
internal elastic membrane membrane composed of elastic fibers that separates the tunica intima from the tunica media seen in larger arteries
interventricular septum cardiac septum located between the two ventricles
left atrioventricular valve (also, mitral valve or bicuspid valve) valve located between the left atrium and ventricle consists of two flaps of tissue
lumen interior of a tubular structure such as a blood vessel or a portion of the alimentary canal through which blood, chyme, or other substances travel
marginal arteries branches of the right coronary artery that supply blood to the superficial portions of the right ventricle
mesothelium simple squamous epithelial portion of serous membranes, such as the superficial portion of the epicardium (the visceral pericardium) and the deepest portion of the pericardium (the parietal pericardium)
metarteriole short vessel arising from a terminal arteriole that branches to supply a capillary bed
microcirculation blood flow through the capillaries
middle cardiac vein vessel that parallels and drains the areas supplied by the posterior interventricular artery drains into the great cardiac vein
mitral valve (also, left atrioventricular valve or bicuspid valve) valve located between the left atrium and ventricle consists of two flaps of tissue
nervi vasorum small nerve fibers found in arteries and veins that trigger contraction of the smooth muscle in their walls
packed cell volume (PCV) (also, hematocrit) volume percentage of erythrocytes present in a sample of centrifuged blood
plasma in blood, the liquid extracellular matrix composed mostly of water that circulates the formed elements and dissolved materials throughout the cardiovascular system
platelets (also, thrombocytes) one of the formed elements of blood that consists of cell fragments broken off from megakaryocytes
red blood cells (RBCs) (also, erythrocytes) one of the formed elements of blood that transports oxygen
thoroughfare channel continuation of the metarteriole that enables blood to bypass a capillary bed and flow directly into a venule, creating a vascular shunt
tunica externa (also, tunica adventitia) outermost layer or tunic of a vessel (except capillaries)
tunica intima (also, tunica interna) innermost lining or tunic of a vessel
tunica media middle layer or tunic of a vessel (except capillaries)
vasa vasorum small blood vessels located within the walls or tunics of larger vessels that supply nourishment to and remove wastes from the cells of the vessels
vascular shunt continuation of the metarteriole and thoroughfare channel that allows blood to bypass the capillary beds to flow directly from the arterial to the venous circulation
vasoconstriction constriction of the smooth muscle of a blood vessel, resulting in a decreased vascular diameter
vasodilation relaxation of the smooth muscle in the wall of a blood vessel, resulting in an increased vascular diameter
vasomotion irregular, pulsating flow of blood through capillaries and related structures
vein blood vessel that conducts blood toward the heart
venous reserve volume of blood contained within systemic veins in the integument, bone marrow, and liver that can be returned to the heart for circulation, if needed
ventricle one of the primary pumping chambers of the heart located in the lower portion of the heart the left ventricle is the major pumping chamber on the lower left side of the heart that ejects blood into the systemic circuit via the aorta and receives blood from the left atrium the right ventricle is the major pumping chamber on the lower right side of the heart that ejects blood into the pulmonary circuit via the pulmonary trunk and receives blood from the right atrium
venule small vessel leading from the capillaries to veins
white blood cells (WBCs) (also, leukocytes) one of the formed elements of blood that provides defense against disease agents and foreign materials
Answer the question(s) below to see how well you understand the topics covered in the previous section.
Critical Thinking Questions
- Identify the ventricle of the heart that pumps oxygen-depleted blood and the arteries of the body that carry oxygen-depleted blood.
- What organs do the gonadal veins drain?
- What arteries play the leading roles in supplying blood to the brain?
[reveal-answer q=&rdquo447815&Prime]Show Answers[/reveal-answer]
- The right ventricle of the heart pumps oxygen-depleted blood to the pulmonary arteries.
- The gonadal veins drain the testes in males and the ovaries in females.
- The internal carotid arteries and the vertebral arteries provide most of the brain&rsquos blood supply.
Background and Purpose—
A noninvasive method with high reliability and accuracy comparable to transesophageal echocardiography for identification of left atrial appendage thrombus would be of significant clinical value. The aim of this study was to assess the diagnostic performance of a dual-enhanced cardiac CT protocol for detection of left atrial appendage thrombi and for differentiation between thrombus and circulatory stasis in patients with stroke.
We studied 83 consecutive patients with stroke (56 men and 27 women mean age, 62.6 years) who had high risk factors for thrombus formation and had undergone both dual-source CT and transesophageal echocardiography within a 3-day period. CT was performed with prospective electrocardiographic gating, and scanning began 180 seconds after the test bolus.
Among the 83 patients, a total of 13 thrombi combined with spontaneous echo contrast and 14 spontaneous echo contrasts were detected by transesophageal echocardiography. All 13 thrombi combined with spontaneous echo contrast were correctly diagnosed on CT. Using transesophageal echocardiography as the reference standard, the overall sensitivity and specificity of CT for the detection of thrombi and circulatory stasis in the left atrial appendage were 96% (95% CI, 78% to 99%), and 100% (95% CI, 92% to 100%), respectively. On CT, the mean left atrial appendage/ascending aorta Hounsfield unit ratios were significantly different between thrombus and circulatory stasis (0.15 Hounsfield unit versus 0.27 Hounsfield unit, P=0.001). The mean effective radiation dose was 3.11 mSv.
Dual-enhanced cardiac CT with prospective electrocardiographic gating is a noninvasive and sensitive modality for detecting left atrial appendage thrombus with an acceptable radiation dose.
Investigation of potential embolic sources is an important diagnostic step in managing patients with acute ischemic stroke or transient ischemic attack, especially when the mechanism is considered to be embolic. Cardiogenic emboli have been estimated to be the causative factor in 20% to 40% of all stroke cases. 1–3
Currently, transesophageal echocardiography (TEE) has emerged as the most sensitive technique for the detection of intracardiac thrombi and is believed to be the single best modality for patients with suspected intracardiac thrombi. 4–6 Although TEE is widely available, it is a semi-invasive test, usually performed under conscious sedation.
A noninvasive method with high reliability and accuracy comparable to TEE for the identification of left atrial appendage (LAA) thrombus would be of significant clinical value. Recent advances in multidetector CT, including improvements in temporal and spatial resolution, now allow accurate and consistent imaging of cardiac structure, including left atrial and LAA anatomy. CT is a sensitive modality for the detection of intracardiac thrombus, which is seen as a filling defect on CT. 7–10 However, spontaneous echo contrast (SEC), as seen by ultrasound, is caused by circulatory stasis in the LAA in patients with atrial fibrillation and can also appear as an apparent filling defect on CT images, thereby mimicking a thrombus. Therefore, it may be difficult to differentiate between a filling defect due to a thrombus and 1 that is due to circulatory stasis secondary to using an early-enhanced CT scan. A previous study reported that an additional delayed-enhanced scan was necessary for differentiating thrombus from circulatory stasis, which might also cause an apparent filling defect and mimic a thrombus on early-enhanced CT images. 10 However, a limitation of 2-phase cardiac CT (CCT) is higher radiation exposure due to the additional delayed-enhanced scan.
In clinical practice, different contrast injection protocols such as biphasic or triphasic protocols were used for coronary artery CT angiography without standardization. However, the main focus of those injection protocols was to optimize contrast opacification of coronary arteries at the same time as using lesser amounts of contrast materials and having lesser streaky artifacts. 11 Therefore, we developed a new dual-enhanced single-phase CCT protocol using prospective electrocardiographic gating for evaluation of intracardiac thrombus and for the differentiation between a thrombus and circulatory stasis. This protocol used double injection of the contrast agent, and the scan was performed only once in the late phase, 180 seconds, after giving the first contrast bolus.
The aim of this study was to assess the diagnostic performance of a new dual-enhanced single-phase CCT protocol using prospective electrocardiographic gating for detection of LAA thrombi and for differentiation between thrombus and circulatory stasis in patients with stroke using TEE as the reference standard.
Our Institutional Review Board approved this study, and patients provided informed consent. From March 2010 to October 2010, 351 consecutive patients were admitted to our hospital for a recent stroke (onset within the previous 7 days). Of these patients, 102 patients who had high risk factors for thrombus formation were prospectively enrolled in this study. High risk factors for thrombus formation were defined as follows: (1) persistent atrial fibrillation (AF) confirmed by electrocardiography 12,13 (2) valve disease assessed by echocardiography, 14–16 including mitral stenosis (at least moderate in severity), previous mitral valve surgery (valve replacement or repair), or severe aortic regurgitation (3) left ventricular dysfunction 17 defined as severe systolic dysfunction (ejection fraction <30%) or cardiomyopathy with moderate systolic dysfunction (ejection fraction <40%) or (4) history of AF documented by 12-lead electrocardiography before the index TEE examination. 18 TEE was performed within 2 weeks (mean time, 6.8 days time range, within 5 to 13 days) of the initial stroke, except in patients with decreased consciousness (n=3), impending brain herniation (n=1), poor systemic conditions (n=3), tracheal intubation (n=2), or failure in introducing the esophageal transducer (n=1). Nine patients who had contrast agent allergy (n=2), renal dysfunction (n=3), or failed to provide an informed consent (n=4) were excluded.
The remaining 83 patients with high risk factors for thrombus formation were included. TEE and CT examinations were performed within a 3-day period (mean, 2.3 days) to determine the cardioembolic source. All patients underwent brain CT (n=62) or brain MRI (n=81) to confirm and characterize the stroke type and to exclude hemorrhage and other pathology. The patients consisted of 56 men and 27 women with ages from 36 to 83 years (mean age, 62.6 years). Baseline clinical characteristics, including systemic hypertension, hyperlipidemia, diabetes mellitus, and smoking habits, were determined from medical records and routine laboratory data.
Subtypes of ischemic stroke were classified according to the Trial of Org 10172 in Acute Stroke Treatment classification system. 19 The stroke subtypes of 83 patients were the following: stroke of undetermined etiology (n=37 [45%]), large-artery atherosclerosis (n=23 [28%]), cardioembolism (n=21 [25%]), and small-vessel occlusion (n=2 [2%]).
CCT scans were performed with a second-generation dual-source CT scanner (Somatom Definition Flash Siemens Medical Solutions, Erlangen, Germany) in the craniocaudal direction during a single breath-hold. Scanning was performed with the second injection of contrast agent, 180 seconds after injection of the first bolus of contrast agent.
No β-blockers were used in any of the enrollees for regulation of heart rate, because the CT was performed to evaluate the intracardiac structure and not the coronary arteries. The mean heart rate was 65±13 beats per minute (range, 53 to 89 beats/minute) during the CT examination.
A test bolus technique was used before image acquisition in each patient. For test bolus scans (first bolus), 50 mL noniodinated contrast agent, iodixanol (320 iodine mg/mL, Visipaque GE Healthcare, Cork, UK), was administered using a power injector (Envision CT, Medrad) at a rate of 5 mL/s through an 18-gauge needle placed into the right antecubital vein. After contrast agent administration, 50 mL saline was administered at a flow rate of 5 mL/s through the same venous access. A region of interest was plotted inside the ascending aorta and a bolus geometry curve was acquired. Curve diagrams were analyzed immediately after acquisition, and the time to maximum enhancement was measured to determine the optimal scan delay.
Using prospective electrocardiographic gating, the scan was started 180 seconds later, after the end of the test bolus scan. The second bolus, composed of 70 mL of nonionic contrast agent, iodixanol (320 iodine mg/mL, Visipaque GE Healthcare), followed by a 50-mL saline solution, was administered intravenously at a rate of 5 mL/s using a power injector (Envision CT Medrad). The scan parameters were as follows: detector collimation, 2×64×0.6 mm slice acquisition, 2×128×0.6 mm by means of a z-flying focal spot gantry rotation time, 280 ms tube voltage, 100 to 120 kV tube current, 280 to 380 mAs and pitch, 0.2 to 0.43 adapted to the heart rate. All prospectively electrocardiographic-triggered studies were centered at 70% of the R-R interval.
Images were reconstructed with a slice thickness of 0.6 mm and a reconstruction increment of 0.4 mm using a soft-tissue convolution kernel (B36f). Radiation exposure was estimated from the dose-length product. The calculated mean radiation dose was 3.11 mSv (dose-length product range, 58 to 411 mGy*cm) depending on the scan range and the patient's body weight.
TEE was performed with a 5- to 7-MHz multiplane probe positioned at the appropriate level within the esophagus. For each patient, all images were recorded on digital video in real time for display and evaluation. Multiple standard tomographic planes were imaged, and LAA-emptying velocity, the presence of left artery or LAA thrombi, and the severity of left artery SEC were determined. SEC was characterized by dynamic clouds of echoes curling slowly in a circular or spiral shape within the LAA cavity. The severity of SEC was divided into 4 grades based on appearance and density using a 5-MHz transducer, as follows: none, the absence of this phenomenon mild, minimal echogenicity only detectable with optimal gain settings transiently during the cardiac cycle moderate, dense swirling pattern during the entire cardiac cycle and severe, intense echodensity and very slow swirling patterns in the LAA, usually with a similar density in the main cavity.
Two experienced radiologists prospectively and independently reviewed the CT images of the 83 patients. Disagreement was resolved by a joint reading. Each reader was blinded to the results of other examinations and clinical data.
On CT, we defined a thrombus as a filling defect that appeared as an oval or round shape on CT images. Circulatory stasis was defined as a filling defect that appeared as a triangular shape in the LAA with homogeneous attenuation on CT images.
For quantitative analysis, we calculated the LAA/ascending aorta (AA) Hounsfield unit (HU) ratio on CT images for thrombus and SEC. For that purpose, regions of interest of approximately 10 mm 2 (range, 5 to 18 mm 2 ) were placed inside the filling defect in the LAA seen on CT images and the AA of the same slice to generate an LAA/AA HU ratio. CT density was independently measured at 2 different selected points in HU by 2 radiologists and the mean LAA/AA HU ratio was used for analysis. Receiver operating characteristic curves were constructed using the HU ratios and the best cutoff value was determined for the differentiation between thrombus and circulatory stasis. Retrospective analysis demonstrated that the best cutoff threshold value for separating thrombus from circulatory stasis was 0.2 (Figure 1).
Figure 1. Receiver operating characteristic (ROC) curve using the Hounsfield unit (HU) ratios. The best cutoff value for separating thrombus from circulatory stasis was 0.2 (sensitivity, 80% specificity, 85%, area under the ROC curve [AUC]=0.885).
Two experienced cardiologists prospectively and independently reviewed the TEE images of the 83 patients and graded the severity of SEC. Disagreement was resolved by a joint reading. On TEE, thrombus was defined as a well-circumscribed, uniformly consistent, echo-reflective mass of different texture from the LAA wall.
Categorical baseline characteristics were expressed as numbers and percentages and were compared between patients with and without thrombus or SEC by means of the χ 2 test. Continuous variables were expressed as mean and SD and were compared with the Student t test for independent samples.
For all imaging modalities, we recorded the number of the detected thrombi and SEC and characterized the diagnoses made by the reviewers as true-positive, true-negative, false-positive, or false-negative. Using TEE as the reference standard, sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CT for detecting LAA thrombi and SEC were calculated 95% CIs were calculated using the method of exact binomial tail areas. 20 The agreement between the detection of thrombi and SEC with CT and TEE was assessed with κ statistics. The statistical significance of differences in mean LAA/AA HU between thrombus and SEC as measured by CT was assessed using the Student t test. The statistical significance of differences in mean LAA/AA HU of thrombus and SEC according to different grades determined by TEE was assessed using 1-way analysis of variance with the Scheffe method. The correlation between LAA/AA HU ratio and LAA-emptying velocity determined by TEE was assessed. Pearson correlation was used to determine the correlation of mean CT density ratio values between the 2 observers. Probability values <0.05 were considered statistically significant. All statistical analyses were performed with SPSS software (Version 18.0 Statistical Package for the Social Sciences, Chicago, IL).
Twenty-eight patients (34%) had AF during CCT and TEE examinations. However, the image quality of all of the CCT and TEE examinations was considered acceptable for the evaluation of intracardiac abnormalities.
The clinical characteristics of the 83 patients are summarized in Table 1. Clinical characteristics were not significantly different between patients with and without thrombus or SEC, except for those in AF. AF was more commonly observed in patients with thrombus or SEC on TEE. On TEE, there were a total of 13 thrombi combined with SEC and 14 SEC without thrombus. One thrombus was located in the left atrium and 12 were located in the LAA. CT detected 26 filling defects in the left atrium or LAA. Of these 26 lesions, 13 filling defects were diagnosed as thrombi combined with circulatory stasis and 13 as circulatory stasis without thrombus (Figures 2 and 3). All 13 thrombi coexistent with SEC were clearly detected by CT. One mild SEC diagnosed on TEE was missed by CT. Using TEE as the reference standard, the overall sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CT for the detection of thrombi and circulatory stasis in the left atrium or LAA were 96% (95% CI, 78% to 99%), 100% (95% CI, 92% to 100%), 99% (95% CI, 93% to 100%), 100% (95% CI, 84% to 100%), and 98% (95% CI, 89% to 100%), respectively.
Table 1. Clinical Characteristics of 83 Patients With Stroke
All study participant demographic data divided by normal or filling defects on LAA on CT findings including clinical variables and embolic source risk factors. LAA filling defects include 13 thrombi and 14 spontaneous echo contrast.
LAA indicates left atrial appendage CVA, cerebrovascular accident EF, ejection fraction AF, atrial fibrillation SD, standard deviation.
* Predefined high risk factors for thrombus formation.
† Dilated cardiomyopathy combined with systolic dysfunction.
Figure 2. Cardiac CT (CCT) and transesophageal echocardiography (TEE) images from a 62-year-old woman with stroke and a left atrial appendage (LAA) thrombus. A, CT demonstrated an oval-shaped filling defect in the LAA (small arrow) with circulatory stasis (large arrows) just distal to the thrombus. A filling defect just distal to the thrombus caused by circulatory stasis showed higher attenuation density than thrombus. B, TEE image obtained 1 day after CCT. TEE demonstrated a thrombus (large arrow) with spontaneous echo contrast (SEC) just distal to the thrombus (small arrows).
Figure 3. Cardiac CT (CCT) and transesophageal echocardiography (TEE) images from a 61-year-old man with stroke and spontaneous echo contrast (SEC). A, CT demonstrated triangular-shaped filling defects in the left atrial appendage (LAA arrows) without an oval-shaped filling defect suggestive of thrombus. B, TEE image obtained 1 day after CCT. TEE demonstrated moderate SEC without any thrombus in the LAA (arrows).
The concordance between detection of thrombus and SEC in the LAA with CT and TEE was high. Fifty-six patients had no thrombus or SEC on either CT or TEE 13 patients had thrombus on both CT and TEE 13 patients had SEC (without thrombus) on both CT and TEE and 1 patient had SEC seen on TEE but not on CT (overall κ=0.975 Table 2). There were no patients with thrombus detected on TEE but not on CT. Of the 13 filling defects diagnosed correctly as thrombus by CT, combined circulatory stasis was categorized on TEE as severe SEC in 6 cases, moderate SEC in 4 cases, and mild SEC in 3 cases. Of the 13 filling defects diagnosed correctly as circulatory stasis without thrombus by CT, SEC was categorized on TEE as severe in 2 cases, moderate in 5 cases, and mild in 6 cases.
Table 2. Concordance Between CT and TEE for the Detection of Thrombus and SEC in the Left Atrial Appendage
TEE indicates transesophageal echocardiography SEC, spontaneous echo contrast.
* Includes thrombus combined with circulatory stasis.
† Includes circulatory stasis without thrombus.
On CT, the mean LAA/AA HU ratios were 0.15±0.06 HU for thrombus, 0.27±0.09 HU for circulatory stasis, and 0.94±0.06 HU for normal (no thrombus or circulatory stasis). The mean LAA/AA HU ratios were significantly different between thrombus and circulatory stasis (P=0.001 Figure 4). However, the mean LAA/AA HU values for severe SEC (0.20±0.03 HU), moderate SEC (0.25±0.08 HU), and mild SEC (0.34±0.11 HU) did not vary significantly among SEC grades determined by TEE (P>0.05). Receiver operating characteristic curve analysis of HU ratio measurements defined 0.2 as the best cutoff threshold value for separating thrombus from circulatory stasis. Using the cutoff value of 0.2, the overall sensitivity, specificity, positive predictive value, and negative predictive value of CT for the detection of thrombi in the left atrium or LAA were 85% (95% CI, 54% to 97%), 94% (95% CI, 84% to 97%), 73% (95% CI, 45% to 91%), and 97% (95% CI, 89% to 99%), respectively.
Figure 4. Box–whisker graph of CT density values (LAA/AA HU) of thrombus, spontaneous echo contrast, and normal groups. The lower and upper ends of the box represent the 25th and 75th percentiles, respectively, and the line across the box indicates the median. The whiskers range from the 5th to 95th percentile. LAA/AA indicates left atrial appendage/ascending aorta HU, Hounsfield unit.
On TEE, the mean LAA-emptying velocities were 15.1±4.2 cm/s for thrombus, 22.2±6.5 cm/s for SEC, and 64.5±15.5 cm/s for normal (no thrombus or SEC). The mean LAA-emptying velocity was significantly different among the 3 groups (P<0.001). However, the mean LAA emptying velocity was not significantly different between thrombus and SEC (P=0.462). The LAA-emptying velocity was positively correlated with the mean LAA/AA HU values by CT (r=0.841).
There was good interobserver agreement for mean LAA/AA HU ratios for the thrombus, circulatory stasis, and normal groups (r=0.897, r=0.861, and r=0.912, respectively).
This study was designed to examine the performance of the dual-enhanced single-phase CCT protocol in comparison with TEE for the detection of thrombus and differentiation between LAA thrombus and circulatory stasis in patients with stroke. This study demonstrates that the new protocol with prospective electrocardiographic gating is a noninvasive and sensitive modality for detecting LAA thrombus. Furthermore, this protocol can also differentiate between thrombus and circulatory stasis and has an acceptable radiation dose.
Thrombi of the left atrium (LA) and LAA are common sources of stroke, and because LA and LAA thrombi are treatable sources of embolism, the detection of thrombi may significantly affect patient management. Currently, TEE is considered the reference standard for the detection of intracardiac thrombus. However, TEE requires special skills for proper performance and interpretation. Additionally, it is a semi-invasive test, usually performed under conscious sedation. 4–6
CT is a very sensitive modality for detection of intracardiac thrombus. However, CT can result in false-positive findings such as circulatory stasis, which is also seen as a filling defect on CT images. Therefore, CT is unable to visually distinguish 100% of circulatory stasis from definite thrombus, which results in reduced specificity. 7–9 Comparing TEE and CCT in 223 patients with AF, Kim et al 8 reported that the sensitivity, specificity, positive predictive value, and negative predictive value for the detection of severe SEC and thrombus using cardiac CT were 93%, 85%, 31%, and 99%, respectively. In our previous study 9 comparing 64-slice CCT and TEE in 101 patients, the sensitivity and specificity of 64-slice cardiac CT for the detection of thrombi in LAA were 100% and 96%. There were 4 false-positive filling defects on CT that were diagnosed as SEC by TEE. It is known that further assessment with delayed imaging of the LAA after 1 to 2 minutes can improve the specificity for distinguishing circulatory stasis from thrombus. 10 However, with this 2-phase protocol, the radiation exposure to the patients increased.
We developed a new dual-enhanced single-phase protocol using prospective electrocardiographic gating for detection of intracardiac thrombus and for simultaneously distinguishing thrombus from circulatory stasis. We used prospective electrocardiographic gating to reduce the radiation dose, and this protocol used double injection of the contrast agent. The scan was performed only 1 time on a delayed phase, 180 seconds, after giving the first contrast bolus. The double injection protocol was performed for differentiation between thrombus and circulatory stasis. Because it is difficult to differentiate LAA thrombus from circulatory stasis during the first pass of contrast, we hypothesized that a double injection of contrast might be able to delineate these 2 phenomena with more certainty because a thrombus and circulatory stasis would have a different attenuation density on delayed phase scanning due to the contrast enhancement of the first contrast bolus. To achieve a sufficient attenuation density difference between thrombus and circulatory stasis on the delayed phase scanning, we used 50 mL of contrast agent for first bolus injection.
In our study, the new CCT protocol showed high sensitivity (96%) and high specificity (100%) in thrombus and circulatory stasis detection in the LA/LAA in patients with stroke as compared with TEE. We had 1 false-negative finding on CT, which was diagnosed as mild SEC on TEE. Because of the time interval between the 2 modalities, the presence or severity of atrial fibrillation could affect this result. However, 13 thrombi and moderate/severe SEC were all correctly detected on CT. Additionally, using this protocol, the mean LAA/AA HU ratios were significantly different between thrombus and circulatory stasis (P=0.001). These results suggest that the new CCT protocol is not only useful for the detection of thrombus, but also useful for differentiation between thrombus and circulatory stasis. However, when we used the best cutoff value of 0.2 HU ratios and calculated the overall sensitivity and specificity of CT for the detection of thrombi, CT showed lower sensitivity (85%) and specificity (94%) compared with visual analysis. This result suggests that quantitative analysis using LAA/AA HU ratios is insufficient for accurate differentiation between thrombus and circulatory stasis.
LAA dysfunction, which is associated with AF in many cases, is also commonly accompanied by SEC. 21,22 It is known that LA and LAA SEC are caused by local blood stasis, which is associated with a high incidence of thrombus formation and thromboembolic events. 23,24 Fatkin et al 24 demonstrated that significant LAA dysfunction is similarly associated with LAA thrombus formation and the degree of LAA SEC is negatively associated with LAA-emptying velocities. In our study, the mean LAA-emptying velocity was significantly different among the thrombus, SEC, and normal groups (P<0.001). However, the mean LAA-emptying velocity was not significantly different between the thrombus and SEC groups (P=0.462).
We evaluated whether any quantitative value on CT can predict LAA function. For that purpose, we calculated the mean LAA/AA HU ratios on CT images. We hypothesized that by using a quantitative measurement of HU within the LAA relative to a reference point, we would be able to evaluate LAA function by CT. Our data revealed that the mean LAA/AA HU ratios were strongly correlated with the LAA-emptying velocity measured by TEE (r=0.841). However, our quantitative analysis showed that CT, as compared with TEE, could not differentiate the severity of SEC. This finding suggests that LAA/AA HU values can indirectly predict the function of the LA and LAA but are insufficient for accurate characterization of the SEC severity in the LA and LAA.
TEE is not only the imaging method of choice for the detection of LAA thrombus or SEC, but is also able to detect cardioembolic sources such as patent foramen ovale, valvular vegetations, or mobile thrombi in the aorta. In addition, in contrast to CT, TEE can be performed in patients with renal dysfunction or an allergy to contrast media. However, TEE is a semi-invasive test. Furthermore, evaluation of SEC and thrombus involves individual judgment that is reader-dependent. Therefore, in clinical practice, a less invasive modality that is capable of assessing for intracardiac thrombus in the setting of embolic stroke is desirable. For that purpose, we believe that CCT with the new protocol we describe in this study can be used as an alternative modality for detecting thrombus in selected patients with stroke, because it has high diagnostic accuracy for the detection of intracardiac thrombus, can distinguish SEC from thrombus, and is a noninvasive and reproducible modality.
Our study had several limitations. First, we did not perform the 2 examinations on the same day. All examinations to evaluate for intracardiac thrombus were performed within a 3-day period. Second, because of the double injection of contrast agent, we used a total of 120 mL of contrast agent, which is a much larger than is usually used for current CCT protocol. However, we believe this amount is acceptable for patients with normal renal function. In our study, the mean blood urea nitrogen and creatinine of the 83 patients with stroke were 15.3 mg/dL (range, 7.4 to 19.8 mg/dL) and 0.91 mg/dL (range, 0.67 to 1.19 mg/dL), respectively. There were no renal complications after the CT examinations. A further limitation was radiation exposure. To reduce the radiation dose, we used a prospective electrocardiographic gating technique and the calculated mean radiation dose was 3.11 mSv. In patients with stroke, when brain CT and CCT are applied to the same patients, the radiation exposure could be increased. Although a small amount of radiation exposure is inevitable, we believe that this protocol provides a means of detecting and ruling out potential intracardiac thrombus in selected patients with stroke and has an acceptable radiation dose.
Dual-enhanced single-scan CCT with prospective electrocardiographic gating is a noninvasive and sensitive modality for detecting LAA thrombus and has an acceptable radiation dose. Furthermore, this protocol can also differentiate between thrombus and circulatory stasis. Therefore, we believe that the new CCT protocol using prospective electrocardiographic gating may be clinically useful for detecting and ruling out intracardiac thrombus in patients at risk for cardioembolic stroke and may pose an alternative diagnostic tool to TEE.
bulbus cordis: portion of the primitive heart tube that will eventually develop into the right ventricle
cardiogenic area: area near the head of the embryo where the heart begins to develop 18&ndash19 days after fertilization
cardiogenic cords: two strands of tissue that form within the cardiogenic area
endocardial tubes: stage in which lumens form within the expanding cardiogenic cords, forming hollow structures
heart bulge: prominent feature on the anterior surface of the heart, reflecting early cardiac development
mesoderm: one of the three primary germ layers that differentiate early in embryonic development
primitive atrium: portion of the primitive heart tube that eventually becomes the anterior portions of both the right and left atria, and the two auricles
primitive heart tube: singular tubular structure that forms from the fusion of the two endocardial tubes
primitive ventricle: portion of the primitive heart tube that eventually forms the left ventricle
sinus venosus: develops into the posterior portion of the right atrium, the SA node, and the coronary sinus
truncus arteriosus: portion of the primitive heart that will eventually divide and give rise to the ascending aorta and pulmonary trunk