The clinical value of frequency analysis of the first heart sound in myocardial infarction

A sensitive technic for frequency analysis of the first heart sound (S 1 ) during isovolumic contraction time (ICT) was developed. Recorded heart sounds were filtered with a dynamic analyzer. Amplitudes of frequencies between 30 and 70 cps were plotted as a percentage of peak total energy of S 1 against frequency. A consistent and reproducible frequency "fingerprint" was obtained in 74 normal subjects. Frequencies of S 1 were shown to be directly proportional to ventricular elasticity (VE) and inversely proportional to combined ventricular mass (VM). VM is constant during ICT. Amplitude at 40 cps was less than at 30 cps because of reduced VE (myocardial infarction), increased VM (athletes), or combined reduction in VE and increased VM (myocardiopathy). Normal patterns were found in aortic insufficiency (increased VE and VM). Diagnostic patterns were found in 21 of 24 patients with acute myocardial infarction (MI) but were similar to patterns found in patients with healed infarcts and myocardiopathy and athletes. Acute pulmonary embolism could be differentiated from MI.