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Transcranial Doppler and acoustic pressure fluctuations for the assessment of cavitation and thromboembolism in patients with mechanical heart valves

^a Department of Surgery, Division of Cardiac Surgery, University of Ottawa Heart Institute, Room H-4403, 40 Ruskin Street, Ottawa, Ontario, K1Y 4W7, Canada
^b Department of Mechanical Engineering, Faculty of Engineering, University of Ottawa, Ottawa, Ontario, Canada

*Corresponding author. Tel.: +1-613-761-4263; fax: +1-613-761-4392.

E-mail address: Rrodriguez{at}ottawaheart.ca (R.A. Rodriguez).

The formation and collapse of vapor-filled bubbles near a mechanical heart valve is called cavitation. Such microbubbles are suspected to have strong pro-coagulant effects. Therefore, cavitation may be a contributing factor to the pro-thrombotic effects of mechanical valves. Herein, we systematically review the available evidence linking cavitation and thrombosis. We also critically appraise the potential usefulness of transcranial Doppler and other new non-invasive diagnostic methods to study cavitation and cerebral embolism in mechanical valve patients. Experimental studies indicate that cavitation microbubbles cause platelet aggregation, complement-activation, fibrinolysis, release of tissue-factor, and endothelial damage. Administration of 100% oxygen to mechanical valve patients during transcranial Doppler examination can transiently decrease the counts of Doppler-detected cerebral microemboli compared with room air. This is associated with removal of most circulating gaseous emboli from cavitation. This method may therefore be applied to the study of cavitation and thromboembolism. Additionally, the analysis of high-frequency acoustic-pressure fluctuations detected from the implosion of cavitation bubbles is a promising method for assessment of cavitation in vivo; however, this requires further development. A better understanding of cavitation is important in order to adequately investigate its role in the overall pro-thrombotic effects in mechanical valve patients. Such studies may allow establishing guidelines for new valve designs.

Key Words: Heart valve prosthesis; Thromboembolism; Transcranial Doppler; Air embolism