Acoustic classification of the state of artificial heart valves

Abstract

Transthoracic acoustic signals from BSCC (Björk-Shiley convexo-concave) mechanical heart valves implanted in human patients were processed to determine if the valves had separated outflow struts. For normal valves with intact outflow struts it is demonstrated that a time-windowed spectral analysis reveals the resonant frequency of the vibrating strut. The strut, which is set into vibration when the valve closes during each cardiac cycle, has a resonant frequency that varies among valves but usually is between 7000 and 8000 Hz. The signal processing technique is based on the hypothesis that the strut's resonant waveform has a smaller decay rate than interfering signals and noise generated upon closure by other mechanical components of the valve. A time window can be selected that optimizes the outflow strut's signal-to-interference ratio. It is shown that the absence of the resonant frequency in the 7000- to 8000-Hz interval is an indication that one of the strut's legs has separated from the valve's flange. This separation of one leg appears to precede the valve's failure that occurs if the other leg also separates from the flange, a state referred to as OSF (outlet strut failure). Acoustic data recorded from 18 clinical patients with implanted valves, that were later explanted and examined, formed the database for this study. Of the 18 valves 9 were SLS (single-leg separated) and 9 were intact (both legs of the outflow strut still attached to the valve's flange). The time-windowed spectral process correctly identified the states of all 18 valves.(ABSTRACT TRUNCATED AT 250 WORDS)