Indication of cavitation in mechanical heart valve patients

Cavitation may cause erosion of prosthetic heart valve material. The phenomenon has been extensively studied in vitro, and an association between the presence of cavitation bubbles and high-frequency pressure fluctuations (HFPF) has been established. In-vivo studies examining this phenomenon are scarce; hence, the study aim was to compare HFPF in patients with native, bioprosthetic or mechanical aortic valves, using both invasive and non-invasive measuring techniques.

Measurements were carried out in 16 patients implanted with a St. Jude Medical aortic valve; two control groups comprised 10 patients with normal aortic valves after coronary artery bypass surgery, and five patients implanted with a Carpentier-Edwards pericardial aortic bioprosthesis. HFPF were measured intraoperatively using a hydrophone placed near the aortic annulus, and postoperatively using the same hydrophone mounted in a specially designed water-filled sound chamber. The frequency spectrum was evaluated using Fast Fourier transformation, and the root mean square (RMS) value of the pressure signals was calculated in the frequency range 50-150 kHz.

HFPF with intensities significantly above the noise floor were registered using both methods in the vicinity of mechanical heart valves. The RMS values of the HFPF for all three patient groups measured intra- and postoperatively disclosed a significant difference between the mechanical valves and the two control groups, indicating that there is no cavitation in the vicinity of the biological or the native valves.

HFPF are present in the vicinity of mechanical aortic valves and can be measured in patients, both invasively and non-invasively. This indication of cavitation was not observed in patients with either native or bioprosthetic aortic valves.