E

Figure 2-32: Right ventricle. A. The right ventricular free wall has been removed to show the archlike crista supraventricularis, which consists of the parietal band (PB), infundibular septum (IS), and septal band (SB). The moderator band (*) joins the septal band to the anterior tricuspid papillary muscle (A). The anteroapical portion of the chamber is heavily trabeculated. M, medial tricuspid papillary muscle; PV, pulmonary valve; RAA, right atrial appendage; RCA, right coronary artery; TV, tricuspid valve. B. The right ventricle has been opened by the inflow-outflow method to show the parietal band (PB) separating the tricuspid and pulmonary valves, as well as the two upper limbs (arrows) of e septal band (SB). A, anterior leaflet of the tricuspid valve; P, posterior leaflet of the tricuspid valve; PT, pulmonary trunk; S, septal leaflet of the tricuspid valve; other abbreviations as in A.

A prominent arch-shaped muscular ridge known as the crista supraventricularis separates the tricuspid and pulmonary valves. It is made up of three components (i.e., parietal band, infundibular septum, and septal band) that may appear as distinct structures or may merge together!517 (see Fig. 2-32). The parietal band is a free-wall structure, whereas the adjacent infundibular septum is intracardiac and separates the two ventricular outflow tracts beneath the right and left cusps of both semilunar valves15'17 (B+;B; Figs. 2-12D and 2-33). The septal band forms a Y-shaped muscle, the two upper limbs of which cradle the infundibular septum. From this branching point of the septal band emanates the medial tricuspid papillary muscle!517 (see Fig. 232). The moderator band forms an intracavitary muscle that connects the septal band with the anterior tricuspid papillary muscle (see Fig. 2-32A).

Left Ventricle

The left ventricle, like the right ventricle, is made of an inlet portion comprised of the mitral valve apparatus, a subaortic outflow portion, and a finely trabeculated apical zone.17 The left ventricular free wall is normally thickest toward the base and thinnest toward the apex, where it averages only 1 to 2 mm in thickness, even in hypertrophied hearts.!7 Structurally, the left and right ventricles differ considerably.15,17 Normally, the left ventricular free-wall and septal thicknesses are three times the thickness of the right ventricular free wall. The mitral and aortic valves share fibrous continuity, whereas the parietal band separates the tricuspid and pulmonary valves. Whereas the mitral valve has an elliptical orifice and no septal attachments, the tricuspid valve has a triangular orifice and numerous direct septal attachments (see Fig. 2-23). The right ventricular apex is much more trabeculated than its counterpart on the left (see BhB; Figs. 2-9i?and E-hB; 2-18 Q. The distinctive differences in apical trabeculations persist even in markedly hypertrophied or dilated hearts.i7

The annular attachment of the septal leaflet of the tricuspid valve inserts more apically than that of the anterior mitral leaflet, allowing distinction between the right and left ventricles by four-chamber imaging (BhB; Fig. 2-34). Exceptions include partial atrioventricular septal defects and double-inlet ventricles in which the two valve annuli are at the same level. Ebstein's anomaly is characterized by exaggeration of apical displacement ofthe septal and posterior tricuspid leaflets resulting in an atrialized portion ofthe right ventricular chamber.iM7 Morphologic differentiation of the right and left ventricles is particularly important in congenital heart disease. The morphologic tricuspid valve virtually always connects to a morphologic right ventricle, whereas the morphologic mitral valve connects to a morphologic left ventricle.!516 Because of the rightward bulging of the ventricular septum, the left ventricular chamber appears circular in cross section, whereas the right ventricular chamber has a crescentic appearance (see Fig. 2-23). Tomographic segmental left ventricular anatomy will be reviewed in the section on coronary arteries.

Left ventricular false tendons, also referred to as pseudotendons or bands,25 are discrete, thin, cordlike fibromuscular structures that connect two walls, the two papillary muscles, or a papillary muscle to a wall, usually the ventricular septum (Fig. 2-35). However, false tendons, as the name implies, are not attached to the mitral leaflets. Chordal attachments between the mitral leaflets and the ventricular septum are abnormal and are usually associated with atrioventricular septal defects or straddling atrioventricular valves.i-6 False tendons are common anatomic variants of the normal left ventricle, occurring in 50 percent of hearts, and may become calcified with age (Q+iSi Fig. 2-36, Plate 12). They are more frequently observed in men, but their incidence does not appear to be age-related.25 It has been suggested that they may be the cause of innocent systolic musical murmurs 25 Although they are readily detectable by echocardiography, they may be misinterpreted by the inexperienced sonographer as pathologic structures such as ruptured chords, mural thrombi, or vegetations.1L25

Tendonul Infundibular

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).

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