| Abstract: | Each of the major cardiac valves (two arterial and two atrioventricular) is made up of a fibrous annulus with a characteristic configuration, and cusps or leaflets comprising a layer of endocardium folded over a fibrous lamina. Each of the arterial valves (aortic and pulmonary) has an annulus shaped like a three-pronged coronet to which are attached three equal-sized semilunar cusps. The arterial wall beyond each cusp forms a pocket or sinus which is crucial in the efficient closure of these valves. The coronary arterial orifices in the aorta lie high in two of the sinuses or above them and are unaffected by valve action. Narrowing of the annulus is a significant component of closure of each cardiac valve, more so for the atrioventricular valves than the arterial. Despite their traditional terminology, the left and right atrioventricular valves (mitral and tricuspid) both possess more than three leaflets each. Closure of these valves is not dependent on the number of leaflets and it is easiest to regard leaflet tissue as a continuous veil or skirt tapering towards the ventricles, where it is tethered to papillary muscles by means of chordae tendineae. Closure of these valves is biphasic, an incomplete phase in late diastole and complete closure during ventricular systole. Movement of atrioventricular leaflet tissue is slight as it is held down by tension of the chordae tendineae. © 1993 Wiley-Liss, Inc. |
