Enlarged Aortic Root Left Atrial Enlargement Sigmoid Septum

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Figure 2-35: Various locations of left ventricular false tendons. A. Two false tendons (arrows) from posteromedial mitral papillary muscle (PM) to ventricular septum (VS), representing the most common location. . . Complex branching false tendon (arrows) with origin from the left ventricular free wall (FW) and insertions into the ventricular septum (VS) and base of posteromedial mitral papillary muscle (PM).

Prominent left ventricular trabeculations26 are another common anatomic normal variant that may be an even greater source of misinterpretation by two-dimensional echocardiography in patients with suspected mural thrombus. They are defined as discrete, thick muscle bundles that generally connect the free wall to the septum (Fig. 2-37). Less common attachments include papillary muscle to the septum, septum to septum, or free wall to free wall. In noncompaction of the left ventricular myocardium,2728 also known as spongy myocardium, there is persistence of multiple prominent ventricular trabeculations and deep intertrabecular recesses caused by arrest in the normal in utero process of myocardial compaction. The associated clinical manifestations and age at onset of symptoms (i.e., typically a dilated cardiomyopathy) are highly variable.

Enlarged Aortic Artery

Figure 2-37: Prominent left ventricular trabeculations. Multiple large muscle bundles extend from the anterior free wall to the septum (probes). A single muscle bundle extends from the posteromedial mitral papillary muscle to the posterior septum (probe with white arrow), and one bundle extends from one portion of the posterior septum to another (probe with black arrow). Such trabeculations become even more prominent in noncompaction of the left ventricular myocardium.

Figure 2-37: Prominent left ventricular trabeculations. Multiple large muscle bundles extend from the anterior free wall to the septum (probes). A single muscle bundle extends from the posteromedial mitral papillary muscle to the posterior septum (probe with white arrow), and one bundle extends from one portion of the posterior septum to another (probe with black arrow). Such trabeculations become even more prominent in noncompaction of the left ventricular myocardium.

Ventricular Septum

The ventricular septum is a complex intracardiac partition that can be considered to comprise four parts: inlet, trabecular, membranous, and infundibular. The plane of the infundibular portion (see

; Figs. 2-12. and 2-33) is different from that of the three other portions. This anatomic relationship is important in many forms of congenital heart disease in which the infundibular septum is dissociated from the remainder of the ventricular septum (e.g., malalignment forms of ventricular septal defects in tetralogy of Fallot and in double-outlet right ventricle).15-17

The ventricular septum also may be divided into muscular and membranous portions15-17 (Figs. 238, Plate 13, and 2-39). The membranous septum lies beneath the right and posterior (noncoronary) aortic cusps (see Fig. 2-30) and contacts the mitral and tricuspid annuli Fig.

2-40, Plate 14). The membranous septum in conjunction with the right fibrous trigone with which it is continuous fuses the commissure between the right and posterior aortic cusps to the commissure between the anterior and septal tricuspid leaflets (see Fig. 2-21B). The majority of clinically significant ventricular septal defects involve the membranous septum.i^ Owing to normal angulation between the infundibular septum and remaining ventricular septum, the septal surface follows the course of an inverted S (moving from apex to aortic valve). The basal half of the ventricular septum is smooth-walled, while the apical half is characterized by numerous small and irregularly arranged trabeculations.!5-17

Membranous Septum

Figure 2-38: (Plate 13) Four-chamber tomographic slice through the aortic root (Ao) and aortic valve (arrows) showing the small membranous (MS) and large muscular (*) portion of the ventricular septum. The membranous septum is divided into atrioventricular (AV) and interventricular (IV) components by the septal tricuspid leaflet (white arrowhead). Black arrowhead points to the expected location of the AV (His) bundle. LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 2-38: (Plate 13) Four-chamber tomographic slice through the aortic root (Ao) and aortic valve (arrows) showing the small membranous (MS) and large muscular (*) portion of the ventricular septum. The membranous septum is divided into atrioventricular (AV) and interventricular (IV) components by the septal tricuspid leaflet (white arrowhead). Black arrowhead points to the expected location of the AV (His) bundle. LV, left ventricle; RA, right atrium; RV, right ventricle.

Aortic Root

Figure 2-39: Tomographic section of the heart along a long-axis plane of the body. The aortic root lies in this plane. The left ventricle and aortic valve are cut obliquely. The membranous ventricular septum (arrow) lies beneath the right and posterior aortic cusps. AoV, aortic valve; Asc Ao, ascending aorta; LA, left atrium; LB, left bronchus; MV, mitral valve; RPA, right pulmonary artery; TS, transverse sinus; TV, tricuspid valve; VS, muscular ventricular septum.

Figure 2-39: Tomographic section of the heart along a long-axis plane of the body. The aortic root lies in this plane. The left ventricle and aortic valve are cut obliquely. The membranous ventricular septum (arrow) lies beneath the right and posterior aortic cusps. AoV, aortic valve; Asc Ao, ascending aorta; LA, left atrium; LB, left bronchus; MV, mitral valve; RPA, right pulmonary artery; TS, transverse sinus; TV, tricuspid valve; VS, muscular ventricular septum.

Clinically relevant age-related anatomic changes include a disproportionate increase in ventricular septal thickness regardless of gender and in the absence of a history of hypertension.20 This is associated with an appreciable increase in the ratio of ventricular septal to left ventricular freewall thickness often exceeding 1.3 in patients older than age 6O20 (H-hB; Fig. 2-41, Plate 15). This may be due in part to accentuation of the sigmoid shape of the basal septum15,20 (Fig. 2-42). Age-related ventricular septal angulation may have clinical importance because it may mimic certain features of hypertrophic cardiomyopathy,1520 particularly if complicated by the indiscriminate use of diuretics or afterload-reducing agents.

Sigmoid Septum

Figure 2-42: Age-related changes in the left-sided cardiac structures. Normal heart from an 84-year-old man demonstrates shortening of the base-to-apex (long-axis) dimension, decreased internal left ventricular dimension, aortic root dilatation, left atrial enlargement, and sigmoid-shaped septum. (Compare with Fig. 2-15 from an 18-year-old man.) Ao, ascending aorta; LA, left atrium; VS, ventricular septum.

Figure 2-42: Age-related changes in the left-sided cardiac structures. Normal heart from an 84-year-old man demonstrates shortening of the base-to-apex (long-axis) dimension, decreased internal left ventricular dimension, aortic root dilatation, left atrial enlargement, and sigmoid-shaped septum. (Compare with Fig. 2-15 from an 18-year-old man.) Ao, ascending aorta; LA, left atrium; VS, ventricular septum.

Atrial Septum

When viewed from its right aspect, the atrial septum is comprised of interatrial and atrioventricular regions16'17 (see Q+-0- Fig. 2-34). The interatrial portion is characterized by the fossa ovalis, which is the anatomic hallmark of a morphologic right atrium Fig. 2-43/1). Its outer muscular rim is a horseshoe-shaped limbus, and its central depression is the valve of the fossa ovalis16'17 (see Fig. 2-43/1). The potential interatrial passageway between the limbus and the valve (which is patent throughout fetal life) is the foramen ovale Figs. 2-43,5 and 2^

44). When viewed from the left atrium, the atrial septum is entirely interatrial, since the atrioventricular component lies below the mitral annulus, between the left ventricle and right atrium. Likewise, the limbus of the fossa ovalis is completely covered by its opaque valve and is not directly visible from the left atrium.15

Enlarged Aorta Heart Scan

Figure 2-44: Tomographic section of the heart along a long-axis of the body. The valve of the fossa ovalis (arrows) and a patent foramen ovale (arrowhead) are seen in this view. Asc Ao, ascending aorta; E, esophagus; IVC, inferior vena cava; LA, left atrium; LB, left bronchus; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle; TS, transverse sinus; TV, tricuspid valve.

Figure 2-44: Tomographic section of the heart along a long-axis of the body. The valve of the fossa ovalis (arrows) and a patent foramen ovale (arrowhead) are seen in this view. Asc Ao, ascending aorta; E, esophagus; IVC, inferior vena cava; LA, left atrium; LB, left bronchus; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle; TS, transverse sinus; TV, tricuspid valve.

The foramen ovale is anatomically closed in about two-thirds of adults, but in the remaining one-third it remains patent and, therefore, a potential source for shunts and paradoxical embolism. Stretching ofthe atrial septum, when the atria are markedly dilated, can transform a patent foramen ovale into an acquired atrial septal defect. The posterior aortic sinus abuts against the interatrial septum (see Fig. 2-12D). During transseptal procedures, care must be taken to stay within the confines of the valve of the fossa ovalis in order to avoid perforation of an aortic sinus.16 Echocardiography may help guide transseptal puncture during balloon mitral valvuloplasty or closure of an atrial septal defect with an occluder device.13 Fenestrations ofthe valve ofthe fossa ovalis are the most common cause ofcongenital atrial septal defects. Redundant valve tissue may form an aneurysm ofthe valve ofthe fossa ovalis.

The atrioventricular (AV) portion of the atrial septum is made of major muscular and minor membranous components and separates the right atrium from the left ventricle16'17 (see 0-»-0-Figs. 2-34 and 2-38). This explains why there is a potential for left-ventricular-to-right-atrial shunts.16.17 The AV septum corresponds roughly to the triangle of Koch, an important anatomic surgical landmark because it contains the AV node and proximal portion ofthe AV (His) bundle. Thus, during tricuspid annuloplasty procedures and patch closures of membranous ventricular septal defects, care must be taken to avoid injury to the conduction system.1617 The muscular component of the AV septum is interposed between the membranous septum anteriorly and the internal cardiac crux posteriorly.

When defects occur in the muscular atrioventricular septum, the mitral annulus usually drops to the same level as the tricuspid annulus, so the defect becomes primarily interatrial (primum atrial septal defect), and the AV conduction tissues are displaced inferiorly. Lipomatous hypertrophy of the atrial septum is characterized by excessive accumulation of adipose tissue within the limbus of the fossa ovalis but always sparing the valve of the fossa74517 Fig. 2-45, Plate 16).

Lipomatous hypertrophy of the atrial septum occurs commonly but not exclusively in older and obese persons.15-17 Although readily detected by echocardiography, it may be misinterpreted as a thrombus or tumor.7

Right Atrium

A prominent internal muscle ridge, the crista terminalis (Fig. 2-46), separates the right atrial free wall into a smooth-walled posterior region that receives the venae cavae and coronary sinus and a muscular anterior region that is lined by parallel pectinate muscles and from which the right atrial appendage emanates.15-17 Pectinatus is Latin for "comb," and the pectinate muscles and crista terminalis resemble the teeth and backbone of a comb, respectively.47 The right atrial appendage abuts the right aortic sinus and overlies the proximal right coronary artery (see Fig. 2-52). The right atrial free wall is paper thin between pectinate muscles and therefore can be perforated easily by stiff catheters.15-17

Pectinate Muscles And Crista Terminalis
Figure 2-46: Right atrial free wall showing separation of the posterior smooth-walled (*) portion from the anterior muscular portion with its pectinate muscles (PeM) and right atrial appendage (RAA) by the crista terminalis (CT). IVC, inferior vena cava; SVC, superior vena cava.
Conus Terminalis

Figure 2-52: The right coronary artery gives rise to the conus branch (CB). A rod retracts the right atrial appendage (*) to disclose the sinus node artery (SNA). Arrow points to an intermediate left coronary artery; arrowhead points to a circumflex marginal branch. L, left aortic cusp; LA, left atrium; LAD, left anterior descending coronary artery; LCX, left circumflex coronary artery; P, posterior aortic cusp; PT, pulmonary trunk; R, right aortic cusp; RUPV, right upper pulmonary vein; SVC, superior vena cava. (From McAlpine,30 with permission.)

Figure 2-52: The right coronary artery gives rise to the conus branch (CB). A rod retracts the right atrial appendage (*) to disclose the sinus node artery (SNA). Arrow points to an intermediate left coronary artery; arrowhead points to a circumflex marginal branch. L, left aortic cusp; LA, left atrium; LAD, left anterior descending coronary artery; LCX, left circumflex coronary artery; P, posterior aortic cusp; PT, pulmonary trunk; R, right aortic cusp; RUPV, right upper pulmonary vein; SVC, superior vena cava. (From McAlpine,30 with permission.)

Inferior vena caval blood flow is directed by the eustachian valve toward the foramen ovale, and superior vena caval blood is directed toward the tricuspid valvei^ (0-hB; Fig. 2-47, Plate 17). Thus transseptal cardiac catheterization is more easily accomplished via the inferior vena cava, whereas instrumentation ofthe right ventricular apex (e.g., endomyocardial biopsy, placement of ventricular pacemaker lead) is more easily accomplished via the superior vena cava.15

Left Atrium

The pulmonary vein orifices lie on the posterolateral (left pulmonary veins) and posteromedial (right pulmonary veins) aspects of the left atrial cavity. The left and right upper pulmonary veins are directed anterosuperiorly, whereas the lower veins enter the left atrium nearly perpendicular to the posterior atrial wall15-17 (Figs. 2-15 and 2-48). Left atrial muscle extends some distance within the pulmonary veins. The resultant cuff of muscle acts as a sphincter during atrial systole and may be the source of focal atrial fibrillation that is amenable to catheter ablation(see Fig. 2-2).

Sigmoid Vein Right Atrium

Figure 2-48: Oblique, short-axis cut at the base of the heart. The esophagus (E) is posterior and adjacent to the left atrium (LA) and adjacent to the descending thoracic aorta (DAo). The left upper pulmonary (LUPV) and left lower pulmonary vein (LLPV) are clearly seen. The right ventricular outflow tract (RVO) is anterior. AS, atrial septum; AoV, aortic valve; LA, left atrium; LAA, left atrial appendage; RA, right atrium.

Figure 2-48: Oblique, short-axis cut at the base of the heart. The esophagus (E) is posterior and adjacent to the left atrium (LA) and adjacent to the descending thoracic aorta (DAo). The left upper pulmonary (LUPV) and left lower pulmonary vein (LLPV) are clearly seen. The right ventricular outflow tract (RVO) is anterior. AS, atrial septum; AoV, aortic valve; LA, left atrium; LAA, left atrial appendage; RA, right atrium.

The atrial appendage arises anterolaterally and lies in the left atrioventricular groove atop the proximal portion of the left circumflex coronary artery and, in some individuals, the left main coronary artery!0 (see Figs. 2-21A and 2-48). The left atrial appendage is smaller, more tortuous, and less pyramidal than its right atrial counterpart.15-17 At least 80 percent are multilobed (up to four lobes, but the most frequent finding is two lobes)20 (B-H0i Fig. 2-49, Plate 18). There are also age- and sex-related differences in the dimensions of the appendage.20 With increasing use of transesophageal echocardiography to search for a cardiac source ofembolism and to guide cardioversion and percutanous balloon valvuloplasty procedures, a thorough appreciation of the variations in normal left atrial appendage morphology has become important because a thrombus may be missed if all lobes in the appendage are not visualized. In contrast to the right atrial free wall, the left has no crista terminalis and no pectinate muscles outside its appendage.15-17

The coronary sinus travels along the posterior wall of the left atrium within the left atrioventricular groove (see Fig. 2-21^4). In patients with persistent left superior vena cava, which most commonly drains into a dilated coronary sinus, the left-sided cava courses between the left atrial appendage and the left upper pulmonary vein.17 The venous structure can be misinterpreted as the descending thoracic aorta, a mass, or a pathologic cavity.

The esophagus and descending thoracic aorta are in contact with the posterior left atrial wall (see Figs. 2-20 and 2-48). Accordingly, esophageal carcinomas may compress, infiltrate, or perforate the left atrium, and descending thoracic aortic aneurysms may compress this chamber.15 A large hiatal hernia also can abut against the left atrium and resemble a mass.

The marked increase in the incidence of atrial fibrillation from the fourth to the ninth decades of life may be due in part to the age-associated dilatation ofthe left atrium.

Coronary Arteries and Veins

A detailed description of the spectrum of coronary artery anatomy including the many variations in the number and size of branches and course of the different arteries is beyond the scope of this chapter. The interested reader is referred to the elegant anatomic work by McAlpine published almost 25 years ago.30 The focus of the discussion that will follow, therefore, is to introduce the reader to the clinically relevant anatomy of the coronary circulation, with special emphasis on tomographic analysis of regional blood flow.

From the right and left aortic sinuses arise the right and left coronary arteries, respectively, and their ostia normally originate about two-thirds the distance from the aortic annulus to the sinotubular junction and about midway between theaortic commissures1517 (Figs. 2-28 and 2-50, Plate 19). Whereas the right coronary artery arises nearly perpendicularly from the aorta, the left arises at an acute angle15 (Fig. 2-51). Rarely, the anterior descending and circumflex arteries arise separately from a double-barrel left coronary ostium.15-17 Ostial stenosis most commonly results from atherosclerosis and degenerative calcification ofthe aortic sinotubular junction, which often overlies the right aortic sinus.117 Less often it is due to aortic dissection or to aortitis associated with syphilis or ankylosing spondylitis. Stenosis ofthe right coronary ostium is much more frequent than that ofthe left. Iatrogenic ostial injury may complicate coronary angiography, intraoperative coronary perfusion, or aortic valve replacement.15-17 Atherosclerosis or thrombosis ofthe most proximal portion of either coronary artery may mimic true ostial stenosis.

Coronary Cusp
Figure 2-51: Differences in angulation at the origins of the right (RCA) and left main (arrow) coronary arteries. L, left aortic cusp; P, posterior aortic cusp; R, right aortic cusp.

The right coronary artery is embedded in adipose tissue throughout its course within the right atrioventricular groove. Tricuspid annuloplasty or replacement may be complicated by injury to the right coronary artery.17 In 50 to 60 percent of persons, its first branch is the conus artery (Fig.

2-52), which supplies the right ventricular outflow tract and forms an important collateral anastomosis (circle of Vieussens), just below the pulmonary valve, with an analogous branch from the left anterior descending coronary artery.15-17 In about a third of patients, the conus artery arises independently from the aorta17 (see Fig. 2-28). The infundibular septum is supplied by the descending septal artery, which usually originates from the proximal right or conus coronary artery.15-17 Among the numerous marginal branches of the right coronary artery that supply the remainder of the right ventricular free wall, the largest branch travels along the acute margin from base to apex15-17 (see B+;0i Fig. 2-50). In at least 70 percent of human hearts, the posterior descending artery arises from the distal right coronary artery (see Fig. 2-50). The posterior descending and distal posterolateral branches of a dominant right coronary artery supply the basal and middle inferior wall, basal (inlet) inferior septum, right bundle branch, AV node, AV (His) bundle, posterior portion of the left bundle branch, and posteromedial mitral papillary muscle.17

The left main coronary artery travels for a very short distance along the epicardium between the pulmonary trunk and left atrium (see Figs 2-50 and 2-52). It then divides into anterior descending and circumflex arteries (see Figs. 2-50 and 2-52). An intermediate artery also may arise at this division, thus forming a trifurcation rather than a bifurcation, and follows the course of a circumflex marginal branch15-17 (see Fig. 2-52).

The left anterior descending coronary artery (LAD) courses within the epicardial fat of the anterior interventricular groove, wraps around the cardiac apex, and travels a variable distance along the inferior interventricular groove toward the cardiac base. Its septal perforating branches supply the anterior septum and apical septum. The first septal perforating branch supplies the AV (His) bundle and proximal left bundle branch17 (Fig. 2-53, Plate 20). In patients with symptomatic hypertrophic obstructive cardiomyopathy, nonsurgical septal reduction by percutaneous transluminal occlusion of septal branches ofthe LAD is a new therapeutic approach aimed at reducing the outflow gradient.31 The long-term effects ofthis procedure are currently unknown. The epicardial diagonal branches of the LAD supply the anterior left ventricular free wall, part of the anterolateral mitral papillary muscle, and the medial one-third of the anterior right ventricular free wall.15-17 Although short segments of the LAD may travel within the myocardium (covered by a so-called myocardial bridge) (Fig. 2-54), the resulting systolic luminal narrowing is probably benign in the vast majority of people.17 However, whereas the prevalence of myocardial bridging is only 0.5 to 1.6 percent in the general population, it is reported to be 28 percent in children and 30 to 50 percent in adults with hypertrophic cardiomyopathy.32 More important, myocardial bridging appears to be associated with a poor prognosis (higher incidence of myocardial ischemia and sudden death) in patients with hypertrophic cardiomyopathy regardless of age.32

Septal Perforator Artery
Figure 2-53: (Plate 20) Septal branches of the left anterior descending coronary artery (LAD); * points to the first septal perforator. (From McAlpine,30 with permission.)
Septal Perforator Picture
Figure 2-54: Intramyocardial course of the left anterior descending coronary artery (arrow).

The left circumflex coronary artery courses within the adipose tissue of the left atrioventricular groove (see Fig. 2-21 A) and commonly terminates just beyond its large obtuse marginal branch (see B-H0i Fig. 2-50). It supplies the lateral left ventricular free wall and a portion of the anterolateral mitral papillary muscle.15-17

Along the inferior surface of the heart, the length of the right coronary artery varies inversely with that of the circumflex artery. The artery that crosses the cardiac crux and gives rise to the posterior descending branch represents the dominant coronary artery. Dominance is right in 70 percent of human hearts, left in 10 percent, and shared in 20 percent.15-17 In patients with a congenitally bicuspid aortic valve, the incidence of left coronary dominance is 25 to 30 percent.i-7

The coronary venous circulation is comprised of coronary sinus, cardiac veins, and thebesian venous systems15-17 Fig. 2-55, Plate 21). The great cardiac vein travels in the anterior interventricular groove beside the left anterior descending coronary artery and in the left atrioventricular groove beside the left circumflex artery.15-17 The great cardiac vein and other cardiac veins, such as the left posterior and middle cardiac veins, drain into the coronary sinus, which courses along the posteroinferior aspect of the left atrioventricular groove and empties into the right atrium15-17 (see &H0; Fig. 2-21/1). The ostium of the coronary sinus is guarded by a crescent-shaped valvular remnant, the thebesian valve. Rarely, the coronary sinus drains directly into the left atrium.!7

During cardiac operations, cardioplegic solution may be administered retrogradely into the coronary sinus. In patients with the Wolff-Parkinson-White preexitation syndrome and left-sided bypass tracts, the ablation catheter during electrophysiologic studies can be positioned within the coronary sinus and great cardiac vein adjacent to the mitral valve ring in order to localize the aberrant conduction pathway.i-7 The coronary veins, via the coronary sinus, provide access to percutaneous epicardial mapping and pacing ofthe ventricles and ablation of subepicardial arrhythmogenic foci33 (Fig. 2-56, Plate 22). Some patients with ischemic cardiomyopathy may be poor candidates for conventional revascularization procedures (e.g., coronary artery bypass graft surgery or angioplasty) because their epicardial coronary arteries are diffusely diseased. Since in virtually all people the coronary veins run parallel to the entire course of coronary arteries, alternative percutaneous revascularization methods that use the coronary veins as a bypass conduit for coronary arterial flow are being explored.34-36 Myocardial revascularization is achieved by either connecting the coronary artery proximal and distal to a stenosis to its companion coronary vein (similar to a conventional bypass graft) or by retroperfusion through the venous microvasculature if the artery and vein are only connected proximal to the stenosis. Coronary veins, unlike saphenous veins, are not removed, thus preserving their adventitia and blood supply.34-36

Transesophageal Pacing
Figure 2-56: (Plate 22) Schematic diagram shows placement of the tip of a pacing/mapping catheter within a coronary vein (arrow) via the coronary sinus (CS). LA, left atrium; LV, left ventricle.

Coronary artery disease is associated with regional abnormalities in ventricular structure and function. Because analysis of segmental myocardial perfusion or contractility is the cornerstone of tomographic imaging techniques [stress echocardiography, SPECT imaging, positron emission tomography (PET), and MRI], for clinicopathologic correlations (Fig. 2-57), a combination tomographic and segmental approach to coronary artery anatomy is recommended.1737 38 Ventricular mass is made of the left and right ventricular free walls and the partitioning ventricular septum. Three levels (i.e., basal, midventricular, and apical) are used to divide the baseapex length of the left ventricle into thirds (Fig. 2-58). The basal third includes that portion between the mitral annulus and the tips of the papillary muscles. The midventricular third is from the papillary muscle to the most apical insertion point of these muscles into the left ventricular free wall. The apical third includes the remainder of the ventricle, from the insertion of the papillary muscles to the left ventricular apex. A similar approach can be applied to the right ventricle.15-17,37 The ventricular septum can be divided into anteroseptal, septal, and inferoseptal segments, and the left ventricular free wall is divided into anterior, lateral, and inferior segments at the basal and midventricular levels (see Fig. 2-58). The left ventricular apical level consists of four segments (i.e., septum, inferior, lateral, and anterior) (see Fig. 2-58).

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  • aija
    When is a sigmoid septum present with atrial enlargement?
    7 months ago

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