Aortic Insufficiency

Abstract

The aortic valve is a tricuspid valve, consisting of two coronary cusps and one noncoronary cusp. In the adult, the aortic valve orifice area ranges from 2.6 to 3.5 cm². Closure of the three cusps in early diastole coincides with the early aortic component (A₂) of the second heart sound, S₂. When there is a leakage of blood in early diastole, this begins at the time of aortic valve closure, producing an early diastolic murmur of decrescendo quality, beginning with A₂ (see Fig. 5.1). The degree of leakage depends upon the magnitude of the area through which the leak occurs, the systemic arterial diastolic pressure, the level of the left ventricular diastolic pressure, and the heart rate. More rapid heart rates tend to shorten diastole more than systole, and thus reduce the amount of regurgitation for each cardiac cycle, but may not change the total amount of blood leaked per unit of time. Higher systemic vascular resistance tends to increase the leak from aorta to left ventricle; hence such vasodilator drugs as the nitrates, hydralazine, and angiotensin conversion enzyme inhibitors tend to decrease the amount of regurgitation. The lower systemic vascular resistance of pregnancy tends to make the murmur less audible. Increasing systemic vascular resistance by sustained hand grip or squatting tends to make the murmur more readily audible. Higher left ventricular end-diastolic pressures, such as may occur with severe acute aortic regurgitation, tend to lessen the duration of the regurgitant period and shorten the aortic diastolic murmur. With severe aortic regurgitation, regurgitant flow may be 50% to 90% of forward flow. A regurgitant area of 0.5 cm² can double left ventricular output. The increased left ventricular stroke output can cause systolic blood pressure to exceed 160 mm Hg (Fowler, 1980).