Origin and appearance of HITS induced by prosthetic heart valves: an in vitro study

Patients with mechanical heart Valve prostheses show significantly enhanced numbers of HITS detected by transcranial Doppler ultrasound. In order to a ssess the origin of HITS formation, an in vitro study was set out to quanti fy valve induced microemboli for mechanical and bioprosthetic valves under various circulatory conditions by means of Ultrasound-Doppler-Sonography. A t the same time the influence of CO2 partial pressure on HITS rate vas inve stigated. If can be summarised that for mechanical heart valve prostheses a strong correlation exists between left ventricular dp/dt(max) and the defe cted HITS rates. It was also demonstrated that a bioprosthesis generates si gnificantly less HITS than a mechanical valve. The origin of HITS is gaseou s since the tests were carried out using a cell-free filtered water-glycero l test fluid. The HITS rate could be increased by increasing the amount of dissolved gas within the test fluid. The results support the hypothesis tha t cavitation is the key factor in the appearance of gaseous microemboli at heart valve prostheses.