Real time sound spectral analysis for diagnosis of thrombosed prosthetic valves.

A real time sound spectral analyzer was developed at the authors' institute and has been used for diagnosis of thrombosed valves for 15 years. The analyzer consists of a wider frequency microphone, a digital signal processor with multiple bandpass filters, and displays. To quantify the high frequency component in section pattern of opening and closing clicks, maximal frequency at -30 dB level was used at a diagnostic parameter (normalized maximal frequency, NMF). A total of 17 thrombosed valves with or without pannus formations have been experienced and SSA showed abnormality in 13 valves, which comprised of Björk-Shiley (N = 6), Starr-Edwards 2320, 6120, 6520 (N = 5) and Kay-Shiley (N = 2). The abnormal findings included NMF of opening or closing clicks lower than normal range of each type of prosthesis, and significant decrease of NMF more than 450 Hz from the value previously obtained. All diagnoses of thrombus formations and their locations were confirmed by operative or autopsy findings. The SSA failed to diagnose in four valves, which comprised of Starr-Edwards 6520 (N = 3) and Björk-Shiley (N = 1). Operative findings revealed that thrombi were formed in a manner that permitted direct collision of disc and valvular ring causing clicks with high frequency component. No pseudo-positive diagnosis for thrombosed valve was experienced in the authors series, and SSA is thought to be a reliable noninvasive technique that enables early diagnosis of a thrombosed valve.