High-frequency pressure fluctuations measured in heart valve patients

Background and nim of the study: Due to the risk of thromboembolic complica tions, mechanical heart valve patients require life-long anticoagulant ther apy, in contrast to bioprosthetic valves. The reason for this is still not fully understood. In vitro studies have demonstrated the presence of cavita tion bubbles in the vicinity of mechanical heart valves, but not of biopros thetic valves. When cavitation bubbles collapse, they release a significant amount of energy, which may damage the formed elements of the blood. A cor relation between the presence of cavitation bubbles and high-frequency pres sure oscillations has been established in vitro. Thus, the aim of this stud y was to measure and quantify high-frequency pressure oscillations in patie nts with normal, bioprosthetic or mechanical aortic valves. Methods: Measurements were performed in six patients with normal aortic val ves after coronary bypass surgery, in five patients fitted with a Carpentie r-Edwards pericardial bioprosthesis, and in nine patients fitted with a St. Jude Medical or CarboMedics aortic valve. High-frequency pressure fluctuat ions were measured intraoperatively using a hydrophone placed near the aort ic annulus. The root mean square (RMS) value of the high-frequency pressure signals were calculated in the frequency range 35-150 kHz. Results: High-frequency pressure fluctuations, with intensities above the n oise floor, were registered only in the vicinity of mechanical heart valve prostheses, and not in the vicinity of normal or bioprosthetic valves. The mean value of RMS pressure fluctuations was 0.5 Pa for normal aortic valves , 0.8 Pa for bioprosthetic valves, and 67 Pa for mechanical valves. Conclusions: This study is the first to show the presence of high-frequency pressure fluctuations in patients with mechanical valves.