Left Ventricular Pseudotendon

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Figure 2-57: Short-axis views. A. Collage of anatomic sections obtained by "bread slicing" the heart in its short-axis plane, corresponding to the tomographic sections obtained by echocardiography and SPECT imaging, viewed from the apex toward the base of the heart. B. Comparable sestamibi SPECT images of the left ventricle showing normal myocardial perfusion at rest and with exercise. SA, short axis.

Anterolateral Heart Ischemia

Figure 2-58: Schematic diagram of the three levels of short-axis tomographic views used in echocardiography for 16-segment wall motion analysis. A, anterior; AL, anterolateral; AS, anterior ventricular septum; I, inferior; IL, inferolateral; IS, inferior ventricular septum; L, lateral; LV, left ventricle; LVOT, left ventricular outflow tract; P, posterior; PL, posterolateral; PS, posterior ventricular septum; RV, right ventricle; S, septum. The most basal segment of the inferior wall is the anatomically true posterior segment. At this level, the adjacent ventricular septum is commonly referred to as either the basal posterior septum or the basal inferior septum and the adjacent lateral wall as either the basal posterolateral wall or the basal inferolateral wall.

Figure 2-58: Schematic diagram of the three levels of short-axis tomographic views used in echocardiography for 16-segment wall motion analysis. A, anterior; AL, anterolateral; AS, anterior ventricular septum; I, inferior; IL, inferolateral; IS, inferior ventricular septum; L, lateral; LV, left ventricle; LVOT, left ventricular outflow tract; P, posterior; PL, posterolateral; PS, posterior ventricular septum; RV, right ventricle; S, septum. The most basal segment of the inferior wall is the anatomically true posterior segment. At this level, the adjacent ventricular septum is commonly referred to as either the basal posterior septum or the basal inferior septum and the adjacent lateral wall as either the basal posterolateral wall or the basal inferolateral wall.

This regional approach is not arbitrary and has been verified by studies of normal, dilated, and hypertrophied hearts. According to this system, there are 16 left ventricular segments that can be evaluated for regional abnormalities. This regional approach also can be used to assess transmural infarct size, because the percentage of left ventricular mass contributed by any particular region is not altered in any significant manner by symmetric hypertrophy or dilatation.!7

Regional Coronary Artery Supply

The ventricular regions described tend to correlate well with common patterns of coronary arterial distribution1517 (Figs. 2-59 and 2-60, Plate 23). Any specific epicardial coronary artery generally will supply a certain cluster of regions. For example, in a typical right-dominant system, the left anterior descending coronary artery would supply the midventricular and basal segments of the anterior and anterolateral walls and anterior septum and all apical segments. The left circumflex artery would supply the midventricular and basal inferolateral segments, and the right coronary artery would supply the midventricular and basal inferior wall and inferior septum (see

; Fig. 2-60). However, because the patterns of coronary distribution are so highly variable, these correlations between coronary blood flow and regional anatomy are not precise. For example, a hyperdominant right coronary artery may supply the apex, and a large, obtuse marginal branch of the circumflex artery may supply the anterolateral or inferior wall. Also, any given myocardial region may, in some people, receive its blood supply from the branches of two independent major epicardial arteries.15-17 In old age, the coronary arteries become dilated and tortuous (Fig. 2-61).

Hyperdominant Lad

Figure 2-59: Regional coronary flow, with a short-axis slice of the heart. A large diagonal branch (D) of the left anterior descending coronary artery (LAD) supplies the lateral wall, and an acute marginal branch (arrowhead) of the right coronary artery (arrow) supplies the anterior right ventricular free wall. The distal segment of the LAD is intramural. RA, right atrium; RV, right ventricle. (From McAlpine,30 with permission.)

Figure 2-59: Regional coronary flow, with a short-axis slice of the heart. A large diagonal branch (D) of the left anterior descending coronary artery (LAD) supplies the lateral wall, and an acute marginal branch (arrowhead) of the right coronary artery (arrow) supplies the anterior right ventricular free wall. The distal segment of the LAD is intramural. RA, right atrium; RV, right ventricle. (From McAlpine,30 with permission.)

Tortuous CoronaryLeft Coronary Artery TortuosityCoronary Microcirculation

Figure 2-61: Tortuous coronary arteries (arrow) typically seen in the elderly with nondilated hearts. Ao, ascending aorta; PT, pulmonary trunk.

Coronary Collaterals and Microcirculation

Collateral channels provide communication between the major coronary arteries and their branches.17 If stenosis of an epicardial coronary artery produces a pressure gradient across such a vessel, the collateral channel may dilate with time and provide a bypass avenue for blood flow beyond the obstruction. Such functional collaterals may develop between the terminal extensions of two coronary arteries, between the side branches of two arteries, between branches of the same artery, or within the same branch (via the vasa vasorum). These are most common in the ventricular septum (between septal perforators of the anterior and posterior descending arteries), in the ventricular apex (between anterior descending septal perforators), in the anterior right ventricular free wall (between anterior descending and right or conus arteries), in the anterolateral left ventricular free wall (between anterior descending diagonals and circumflex marginals), at the cardiac crux, and along the atrial surfaces (between the right and left circumflex arteries).17

The intramural coronary vessels form the microcirculation. There are age-related variations in the pattern of distribution of the coronary microcirculation.39 Angina-like chest pain in some patients with angiographically normal epicardial coronary arteries (i.e., syndrome X, or microvascular angina) may be secondary to abnormal vasodilator reserve or vasoconstriction of the coronary microcirculation.40 Abnormal flow reserve ofthe coronary microcirculation is seen in both dilated and hypertrophied hearts. In the latter, structural changes in the coronary arterioles can be found on histologic examination ofthe myocardium.41-43 In patients with symptomatic hypertrophic cardiomyopathy without angiographic evidence of epicardial coronary artery disease, myocardial tissue obtained during surgical myectomy may show smaller than normal coronary arteriolar lumina.43 Postmortem analysis of hearts with hypertrophic cardiomyopathy also has revealed coronary arterioles with abnormally thick walls.43 With contrast echocardiography, it may be possible to noninvasively visualize intramyocardial arterioles and study coronary How reserve.44 Demonstration of an intact microvascular circulation in akinetic myocardium following acute myocardial infarction, using PET or SPECT imaging or contrast echocardiography, is evidence ofviability ofthe affected segment.44 The creation of intramyocardial channels with CO2 laser transmyocardial revascularization has been associated with augmentation of collateral How to ischemic myocardium through angiogenesis.45 Cardiac Lymphatics

The myocardial lymphatics drain toward the epicardial surface, where they merge to form the right and left lymphatic channels, which travel in retrograde fashion with their respective coronary arteries. These two lymphatic channels travel along the ascending aorta and merge before draining into a pretracheal lymph node beneath the aortic arch. This single lymphatic channel then travels through a cardiac lymph node, between the superior vena cava and innominate artery, and finally empties into the right lymphatic duct. Metastatic tumor obstruction of epicardial lymphatics can produce a pericardial effusion.15-17

Great Vessels

The subclavian and internal jugular veins merge bilaterally to form the right and left innominate veins (Fig. 2-62). Valves in the subclavian and internal jugular veins, near their junctions with the innominate veins, are important anatomic structures that help maintain unidirectional antegrade blood flow not only in the normal state but also in the setting of elevated right-sided heart filling pressures.46 Subclavian and internal jugular venous valves are absent in 2 and 6 percent of people, respectively, and venous valves may be damaged by catheter-induced trauma or by age.46 Absent or malfunctioning valves may interfere with the success of closed-chest cardiopulmonary resuscitation and contribute to the development of brain edema during such a procedure.46

Left Fibrous Trigone
Figure 2-62: The longer left (LIV) and shorter right (RIV) innominate veins normally join to form the right superior vena cava (SVC). Ao, ascending aorta; PT, pulmonary trunk.

The left innominate vein is two to three times the length of its right-sided counterpart. It travels anteriorly to the aortic arch along the right anterolateral border of the ascending aorta, where it joins the shorter right innominate vein to form the superior vena cava15-17 (see Fig. 2-62).

Transesophageal echocardiography imaging of the upper ascending aorta may show a double lumen (i.e., aorta and adjacent innominate vein) that can be misinterpreted as aortic dissection by an inexperienced echocardiographer.7

The superior vena cava lies anterior to the right pulmonary artery Fig. 2-63) and receives the azygos vein posteriorly before draining into the superior aspect of the right atrium, just posterior to the atrial appendage1517 (see Figs. 2-46, Q-nHí 2-47, and 2-63). The vein of Marshall forms the terminal connection between a persistent left superior vena cava and the coronary sinus. Its vestigial remnant in normal adults is the ligament of Marshall (0* Fig 264, Plate 24). Both vein and ligament are a potential source of arrhythmias. The ostium of the inferior vena cava is guarded by a crescent-shaped, often fenestrated flap of tissue, the eustachian valve1517 (see Fig. 2-16/1), that is readily seen by echocardiography. Although generally small, the eustachian valve may become so large that it can produce a double-chambered right atrium.!6 Also, when either the eustachian or thebesian valve is large and fenestrated, it is referred to as a Chiari net.15-17 By echocardiography, a Chiari net may be misinterpreted as a mass.

The thoracic aorta arises at the level of the aortic valve and is divided into three segments: http://cardiology.accessmedicine.com/server-java/Arknoid/amed/hurst/co_chapters/ch002/ch002_p03.html (34 / 39) [2003-1-4 11:45:06]

ascending aorta, aortic arch, and descending thoracic aorta (Fig. 2-65). The ascending aorta consists of sinus and tubular portions, which are demarcated by the sinotubular junction (Figs. 228 and 2-66). This is the site at which supravalvular aortic stenosis is often most severe.15-17

The Artery Four Steps

Figure 2-65: Thoracic aorta. The entire thoracic aorta has been cut in a tomographic manner. The aortic arch travels over the left bronchus and the right pulmonary artery. Asc Ao, ascending aorta; AoV, aortic valve; CS, coronary sinus; Desc Ao, descending thoracic aorta; E, esophagus; IA, innominate artery; IV, innominate vein; LA, left atrium; LB, left bronchus; LCCA, left common carotid artery; LS, left subclavian artery; LV, left ventricle; MV, mitral valve; RPA, right pulmonary artery; RVO, right ventricular outflow; TS, transverse sinus; VS, ventricular septum.

Figure 2-65: Thoracic aorta. The entire thoracic aorta has been cut in a tomographic manner. The aortic arch travels over the left bronchus and the right pulmonary artery. Asc Ao, ascending aorta; AoV, aortic valve; CS, coronary sinus; Desc Ao, descending thoracic aorta; E, esophagus; IA, innominate artery; IV, innominate vein; LA, left atrium; LB, left bronchus; LCCA, left common carotid artery; LS, left subclavian artery; LV, left ventricle; MV, mitral valve; RPA, right pulmonary artery; RVO, right ventricular outflow; TS, transverse sinus; VS, ventricular septum.

Cardiac Transverse Sinus

Figure 2-66: Tomographic section of the heart in the frontal plane of the body showing the aortic sinotubular junction (dashed line). Ao, ascending aorta; AoV, aortic valve; LCCA, left common carotid artery; LV, left ventricle; PT, pulmonary trunk; RA, right atrium; RV, right ventricle; LV, left ventricle; VS, ventricular septum.

Figure 2-66: Tomographic section of the heart in the frontal plane of the body showing the aortic sinotubular junction (dashed line). Ao, ascending aorta; AoV, aortic valve; LCCA, left common carotid artery; LV, left ventricle; PT, pulmonary trunk; RA, right atrium; RV, right ventricle; LV, left ventricle; VS, ventricular septum.

Behind the aortic valve cusps are three outpouchings, or sinuses (of Valsalva). The right aortic sinus abuts against the ventricular septum and right ventricular parietal band and is covered in part by the right atrial appendage (see Figs. 2-30 and 2-52). In contrast, the left aortic sinus rests against the anterior left ventricular free wall and a portion of the anterior mitral leaflet, abuts the left atrial free wall, and is covered in part by the pulmonary trunk and left atrial appendage (see Figs. 2-20 and 2-21 A). The posterior (noncoronary) aortic sinus overlies the ventricular septum and a part of the anterior mitral leaflet, forms part of the transverse sinus, abuts the atrial septum, and indents both atrial free walls1517 (see Figs. 2-12.D and 2-22). Rupture of the right and posterior aortic sinuses of Valsalva may result in a communication with the right ventricular outflow tract or right atrium, whereas rupture of the left aortic sinus of Valsalva leads to a communication with the left atrium or left ventricular outflow tract. Annuloaortic ectasia is associated with hypertension, aortic medial degeneration, and advanced age and may produce aortic regurgitation, ascending aortic aneurysm, or aortic dissection.15-1

The aortic arch gives rise to the innominate, left common carotid, and left subclavian arteries in that order (see Fig. 2-65). In about 10 percent of people, the innominate and left common carotid arteries share a common ostium, and in 5 percent of people, the left vertebral artery arises directly from the aortic arch, between the left common carotid and left subclavian arteries.17 The ligamentum arteriosum (ductal artery ligament) represents the vestigial remnant of the fetal ductal artery, which when patent connects the proximal left pulmonary artery to the undersurface of the aortic arch.17 Most coarctations occur just distal to the left subclavian artery (see Fig. 2-69). When thoracic aortic dissection does not involve the ascending aorta (Debakey type IIIand Stanford type B), the intimal tear is commonly near the ligamentum arteriosum or the ostium of the left subclavian artery.i7 Nonpenetrating deceleration chest trauma, as may occur in motor vehicle accidents, commonly involves the aorta in the region between the aortic arch and descending thoracic aorta and may be associated with aortic transection or pseudoaneurysm formation.17

Timing Subclavian
Figure 2-69: Real-time three-dimensional CT reconstruction of the thoracic aorta in a patient with coarctation (arrow) distal to the left subclavian artery. AoV, aortic valve. Desc, descending thoracic aorta.

The descending thoracic aorta lies adjacent to the left atrium, esophagus, and vertebral column. The pulmonary trunk (or main pulmonary artery) emanates from the right ventricle and travels to the left of the ascending aorta. As it bifurcates, the left pulmonary artery courses over the left bronchus, whereas the right pulmonary artery travels beneath the aortic arch and behind the superior vena cava (see Figs. 2-1 IA and 2-63). Thus the left bronchus and the right pulmonary artery normally travel beneath the aortic arch.

Cardiac Conduction System

The cardiac conduction system consists of the sinus node, internodal tracts, AV node, AV (His) bundle, and right and left bundle branches1517 Fig. 2-67, Plate 25). The sinus node is located sub-epicardially in the terminal groove, close to the junction between the superior vena cava and right atrium. The sinus node artery arises from the right coronary artery in 55 percent of people. Its course may place it in contact with the base of the right atrial appendage and the superior vena cava-right atrial junction (see Fig. 2-52). When the sinus node artery arises from the left circumflex artery (45 percent), it may course close to the left atrial appendage. During such surgical operations as the Mustard and Fontan procedures, the sinus node and its artery are susceptible to injury..1M7

By light microscopy, there are no morphologically distinct conduction pathways between the sinus and AV nodes.17 However, electrophysiologic studies support the concept of functional preferential pathways that travel along the crista terminalis and atrial septum including the limbus but not the valve of the fossa ovalis.17 Internodal conduction disturbances therefore are not expected as a result of transseptal procedures. With the Mustard operation for complete transposition ofthe great arteries, there may be severe disturbance of internodal conduction because the entire septum is resected, and the surgical atriotomy may disrupt the crista terminalis.17 Lipomatous hypertrophy ofthe atrial septum may interfere with internodal conduction and induce a variety of atrial arrhythmias. Ventricular preexcitation is most commonly associated with aberrant bypass tracts that span the annulus ofthe tricuspid or mitral valve (see Fig. 2-2).

The AV node, in contrast to the sinus node, is a subendocardial structure that is located within the triangle of Koch1517 Fig. 2-68, Plate 26). The triangle of Koch is bordered by the coronary sinus ostium posteroinferiorly and the septal tricuspid annulus anteriorly. Because of its right atrial location near the tricuspid annulus, the AV node is susceptible to injury during tricuspid annuloplasty and during plication procedures for Ebstein's anomaly.15-17

The AV (His) bundle arises from the distal portion of the AV node and travels along the ventricular septum adjacent to the membranous septumi^17 (see Fig. 2-68). The AV conduction tissue is generally remote from the defect in the outlet, inlet, and muscular forms of ventricular septal defect but travels along the inferior margin of a membranous ventricular septal defect. The AV bundle travels through the central fibrous body (right fibrous trigone) and therefore is closely related to the annuli of the aortic, mitral, and tricuspid valves. Thus, during operative procedures involving these valves or a membranous ventricular septal defect, care must be taken to avoid injury to the His bundle. Whereas in normal hearts the AV bundle courses along the posteroinferior rim ofthe membranous septum, it courses along the anterosuperior rim ofthe membranous septum in hearts with AV discordance. The AV bundle receives a dual blood supply from the AV nodal artery and the first septal perforator of the left anterior descending coronary artery.17

The right bundle branch emanates from the distal portion of the AV bundle and forms a cordlike structure that travels along the septal and moderator bands toward the anterior tricuspid papillary muscle (see Fig. 2-67). In contrast, the left bundle branch represents a broad fenestrated sheet of subendocardial conduction fibers that spread along the septal surface of the left ventricle1517 (see Fig. 2-67). The right and left bundle branches receive dual blood supply from the septal perforators of the left anterior descending coronary artery and posterior descending coronary arteries.17 Left ventricular pseudotendons may contain conduction tissue from the left bundle branch.17 Following right ventriculotomy for reconstruction ofthe right ventricular outflow tract, the ECG shows a pattern of right bundle-branch block even though the right bundle is not disrupted.116

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