Continuous spectral analysis of heart murmurs for evaluating stenotic cardiac lesions

Severity of stenotic heart lesions affects timing, quality and pitch of associated heart murmurs. This quantitative study investigated the relation between instantaneous sound frequencies contained in heart murmurs and magnitudes of Doppler jet velocities measured distal to associated obstructions. Heart murmurs were recorded from 18 patients, ages 1 day to 23 years, with 21 separate murmurs resulting from abnormal valves (18 studies) or left-to-right shunts (3 studies). Recorded murmurs were digitized and divided into 12.3-ms time segments for computer frequency analysis using the maximum entropy method. Murmur spectra were plotted in gray scale against time. All murmurs contained dominant frequencies that varied with time. Dominant murmur frequencies and associated Doppler jet velocities at equivalent points in time were measured at 50-ms intervals. For 88 points analyzed, instantaneous dominant frequencies ranged from 130 to 410 Hz (mean +/- standard deviation 282 +/- 70 Hz) and instantaneous jet velocities ranged from 110 to 460 cm/s (290 +/- 80 cm/s). For the 21 murmurs studied, peak murmur frequencies ranged from 200 to 410 Hz (308 +/- 70 Hz) and peak jet velocities ranged from 165 to 460 cm/s (320 +/- 78 cm/s). Instantaneous dominant frequency correlated to instantaneous jet velocity (r = 0.85) and peak dominant frequency correlated to peak jet velocity (r = 0.89). This in vivo study demonstrates that dominant frequencies contained in heart murmurs are related to instantaneous jet velocities distal to associated obstructions.