The phonocardiogram of aortic stenosis.

Aortic stenosis produces a systolic murmur of characteristic shape in the phonocardiogram both in the aortic and mitral areas. Sound records were taken in 20 patients with aortic stenosis. Thq phonocardiograph used for this investigation has been described elsewhere (Leatham, 1949), and consisted of crystal microphones, valve amplifiers, and both string and mirror galvanometers. Filters were u-sed to reduce the intensity of the low frequencies to about the same extent as effected by the human hearing mechanism; the resulting curve is called high frequency or logarithmic (Rappaport and Sprague, 1941). Records from the aortic and mitral areas were often made simultaneously. In each patient there was good clinical evidence of aortic stenosis and in 13 of them calcification of the aortic valve was seen on fluoroscopy. Any patient with a mitral diastolic murmur, whether audible or recorded by the phonocardiograph, or with radiological evidence of left auricular enlargement was excluded from the series. The onset, shape, and termination of the systolic murmurs in these patients are represented by the diagram in Fig. 1, and phonocardiograms are shown in Fig. 2 to 6. The exact moment of onset of a systolic murmur is difficult to determine for it may be confused with high frequency components of the first sound, but appeared to start immediately after the first sound in some or later in others, as pointed out by Evans (1947). In 19 of the 20 cases in the present investigation the vibrations were small at first, rose to a peak in mid-systole, and then diminished in size until they were small or absent before the second sound; in one subject (Case 10) the accentuation was earlier in systole. This symmetrical pattern with mid-systolic accentuation was usually best seen in the aortic area, but was always present in the mitral area too. A second sound was always recorded though in some it may have been pulmonary in origin. A diastolic murmur following the second sound was heard and recorded in 13 subjects. An aortic systolic murmur of the shape described does not occur in stenosis only, for it is found in aortic sclerosis, coarctation of the aorta, and syphilitic aortic incompetence (Fig. 7). The systolic murmur of mitral valve disease was found to be of different shape. it usually started immediately after the first sound and continued to the second sound with no sharp midsystolic accentuation (Fig. 8 and 9). In some patients with mitral incompetence the murmur was mainly in late systole. In pulmonary stenosis the systolic murmur was usually different from that in aortic stenosis. There was less mid-systolic accentuation and the murmur extended to the second sound or beyond it (Fig. 10).