Determinants of the amplitude of the aortic component of the second heart sound in aortic stenosis

The characteristics of the aortic component of the second heart sound in calcific and congenital noncalcific aortic stenosis were studied to determine a cause for observed differences. Intraarterial pressure and sound were measured above the aortic valve in 20 patients utilizing catheter-tip micromanometers. Ten patients had a normally functioning aortic valve, six had calcific aortic stenosis and four had congenital noncalcific aortic stenosis. As expected, the aortic sound was diminished in patients with calcific aortic stenosis compared with that in patients with a normal valve (600 ± 200 versus 2,600 ± 200 dynes/cm² (P < 0.001). In patients with congenital aortic stenosis, sound amplitude was not reduced compared with that in patients with a normal valve. Measurement of sound produced by closure of normal and stenotic valves in an in vitro model of the circulatory system yielded comparable results. In vitro high speed (2,000 frames/sec) motion pictures of the diastolic motion of the closed cusps showed vibrations of comparable magnitude in the normal porcine and the simulated congenitally stenotic valve. The calcified stenotic valve showed no noticeable diastolic vibrations. These observations indicate an association between the amplitude of the second heart sound and diastolic vibrations of the closed cusps. A calcified stenotic valve, being thick and stiff, would have a diminished ability to vibrate and would therefore produce a diminished sound. A congenitally stenotic valve, in contradistinction, if not yet damaged by degenerative changes, would not be limited in its ability to vibrate during diastole and would therefore produce a normal second sound.