1.4: The Ventricles
- Page ID
- 43818
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The Morphologically Right Ventricle
Description of the ventricular chambers is facilitated by considering them in terms of three components - inlet, apical trabecular and outlet. The inlet contains the atrioventricular valve and its tension apparatus; the outlet supports the arterial valve. The apical trabecular portion is the most distinctive in each ventricle being characteristically coarse in the right ventricle (Figure 1.4.1A) and fine in the left ventricle. In a similar way, the muscular ventricular septum can be considered in terms of inlet, apical trabecular and outlet portions. A small fibrous area, the membranous septum, is located at this tripartite junction. The attachment of the septal tricuspid valve leaflet divides the membranous septum into atrioventricular and interventricular components (Figure 1.4.1B). It is important to appreciate that the entire ventricular septum is not on one plane. Owing to the 'wrap-around' relationship of the right ventricle to the left ventricle, the various portions are arranged at angles to each other. The inlet septum (between the ventricular inlet portions) is more or less at the sagittal plane of the body. Extending out apically and curving between the inlet and outlet components is the trabecular septum. In lateral projection, the right ventricle is seen to sweep from beneath to above the left ventricle. When viewed in frontal projection the right ventricle passes in front of the left ventricle (Figure 1.1.1). A prominent Y-shaped muscle band, the septomarginal trabeculation, is adherent onto the septal surface. Clasped in between the limbs of the septomarginal trabeculation is the supraventricular crest, a distinctive feature of the right ventricle. The tricuspid valve is separated from the pulmonary valve by this crest (Figure 1.4.1A). Much of the crest is simply the infolded inner heart curvature with fatty tissue containing the right coronary artery on its epicardial aspect. The body of the septomarginaI trabeculation gives origin to the moderator band that crosses the ventricular cavity to insert to the anterior wall. The right ventricular inlet component extends from the tricuspid valve orifice to the attachment of the papillary muscle but a discrete demarcation is not seen. The tricuspid valve lacks a well-formed fibrous annulus. Its three leaflets are not always easy to identify owing to clefts within its major leaflets. The commissural chords will identify the divisions between the three leafets - the antero-superior, the septal and the postero-inferior. The direct attachment of the septal leaflet to the septum is a distinguishing feature of the tricuspid valve.
The Morphologically Left Ventricle
In contrast to the right ventricle, the left ventricle is a conical structure with thick tubular walls tapering to a rounded apex (Figure 1.3.2A) where the apical wall becomes as thin as 1-2 mm. Very little of the left ventricle is visible from the front of the heart (Figures 1.1.1 and 1.2.3A) although in the infant a relatively greater portion may be seen. As with the right ventricle, the left ventricle comprises inlet, trabecular and outlet portions. The acute angle between inlet and outlet portions brings the aortic valve in adjacency and in fibrous continuity with the mitral valve. There is no structure comparable to the supraventricular crest in the left ventricle. There is also no structure corresponding to the septomarginal trabeculation on the smooth septal surface (Figure 1.4.2A).
The inlet component surrounds and contains the mitral valve and its tension apparatus. The outlet component supports the aortic valve but only half its circumference is muscular while the other half is an area of fibrous continuity between aortic and mitral valves. The aortic (antero-superior) leaflet of the mitral valve is suspended like a curtain between the inlet and outlet components. The deeply wedged posterior position of the aortic outflow tract displaces the mitral valve leaflets away from the septum as contrasted with the septal attachment of the tricuspid valve. The trabecular component has characteristically fine trabeculations (Figure 1.4.2A).
The mitral valve annulus is thickened at each commissure to form the left and right fibrous trigones. The annular attachment of the aortic (or anterior) leaflet is related to the membranous septum and right fibrous trigone (together making the central fibrous body). The other leaflet of the mitral valve - the mural (or posterior) leaflet - usually has three scallops. The mitral valve is supported by two groups of papillary muscles in antero-lateral and postero-medial positions. Although textbook pictures tend to portray the papillary muscles as arranged far apart, they are in reality situated close to one another. Each papillary muscle supports the adjacent part of both leaflets and the commissures are marked by fan-shaped commissural chords. The outlet component supports the aortic valve. The semilunar leaflets are attached within the expanded aortic sinuses (of Valsalva). The sinuses are not strictly in right and left position although they are so designated in consideration of the origins of the coronary arteries. The central position of the aorta places it in close relation to each of the cardiac chambers and valves (Figure 1.4.2B).
The commissure between right and left coronary cusps is usually positioned opposite a commissure of the pulmonary valve. The commissure between the left and non-coronary leaflets points towards the left atrium. The commissure between right coronary and non-coronary leaflets lies above the membranous septum and is closely related to the right atrium and right ventricle and the atrioventricular conduction bundle (Figure 1.4.2B).