The Cardiac Valves

The interrelationship between the aortic, pulmonary, mitral and tricuspid valves is quite uniform. The pulmonary valve is somewhat anterosuperior and to the left of the aortic valve. The annulus of the aortic, mitral, and tricuspid valves merge with each other and the membranous septum to form the fibrous skeleton of the heart. The anterior leaflet of the mitral valve is in fibrous continuity with portions of the left and noncoronary aortic cusps. This skeleton has left and right fibrous trigones. The right fibrous trigone is the junction between the mitral, tricuspid, and aortic annuli and the membranous septum, and is pierced by the bundle of His; as noted above this is the most dangerous place for injuring conduction tissue when performing a mitral, aortic, or tricuspid valve replacement. The left fibrous trigone is situated more to the left and lies between the left aortic cusp and mitral annulus.

TRIANGLE OF KOCH :

septal leaflet

Fig. 1.2. Interior of the right atrium as seen from the surgeon's view.

Fig. 1.2. Interior of the right atrium as seen from the surgeon's view.

TRIANGLE OF KOCH :

septal leaflet

Mitral Valve Node
AV NODE/BUNDLE OFHIS

Mitral valve

The mitral valve is bicuspid with an anterior (septal) leaflet and a posterior (mural) leaflet. Figure 1.1a shows that the anterior mitral leaflet has a much larger area than the posterior leaflet, but the circumference of the posterior leaflet is much larger than the anterior leaflet, hence the smile configuration of mitral valve. The septal or anterior leaflet is in fibrous continuity with the aortic valve through the aortic mitral annulus as described above. The region of continuity occupies about one quarter of the mitral annulus and corresponds to the region between half of the left coronary cusp and half of the noncoronary cusp of the aortic valve

The limits of this attachment are demarcated by the right and left fibrous trigones. These points do not correspond to the commissures of the mitral valve, although the commissures are close. The AV node and bundle are at risk of surgical damage because of the proximity to the right trigone which is adjacent to the right and noncoronary cusp of the aortic valve and to the septal and anterior leaflet of the tricuspid valve.

The posterior leaflet, although smaller, occupies more of the circumference of the mitral valve annulus. The chordae tendineae to the mitral valve originate from the anterolateral and posteromedial papillary muscles. Each leaflet receives chordae from both muscles with the majority inserting on the free leaflet edge. There are three orders of chordae: the first order insert on the free margin of the leaflet; the second order chordae insert several millimeters back from the free edge; and the third order chordae insert at the base of the leaflet. Third order chordae exist only on the posterior leaflet.

Tricuspid Valve

The annulus of the tricuspid valve is relatively indistinct, compared with the mitral valve, especially in the region of the septal leaflet. The leaflets and chordae are thinner than that of the mitral valve. The anterior leaflet is the largest of the leaflets; the posterior leaflet is usually smallest; the septal leaflet is larger than the posterior leaflet. Of major importance is the proximity of the septal and anterior leaflet commissure to the membranous septum immediately adj acent to the bundle of His which penetrates the right trigone in this region.

Aortic valve

This is a tricuspid valve consisting of a right, left and noncoronary cusps. The aortic valve is in fibrous continuity with the anterior leaflet of the mitral valve and the membranous septum. The walls of the coronary sinuses are thinner than the wall of the remainder of the aorta itself.

Pulmonary Valve

The structure of the pulmonary valve is similar to the aortic valve. The pulmonary valve has three cusps which are lighter than that of the aortic cusps.

Pulmonary valve cusps are described by several terminologies, but usually by their relationship to the aortic valve, i.e. right, left and anterior pulmonary cusps.

Fibrous Skeleton Aortic Valve
Fig. 1.3. Anatomic relationship of the anterior leaflet of the mitral valve and the aortic valve.
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