Microbubbles and mitral valve prostheses - transesophageal echocardiographic evaluation

To assess whether microbubbles are associated with a specific type of mitral valve prosthesis and to investigate the relationship of microbubbles to ventricular function and mitral regurgitation. One of the types of spontaneous echocardiographic contrast observed in patients with prosthetic heart valves has been described as microbubbles.

Clinical data and videotapes of patients with a prosthetic mitral valve who had undergone transesophageal echocardiography at the UCLA Medical Center between May 1989 and February 1995 were retrospectively reviewed. There were 109 studies (74 patients) available for review by two independent observers.

Microbubbles occurred in 49 of the 66 studies of St. Jude valves ( 74%), eight of the 12 studies of Bjork Shiley valves (67%), four of four studies of Medtronic valves (100%) and zero of 23 studies of tissue valves (0%). Patients with an estimated ejection fraction greater than 45% were found to have a much higher likelihood of having microbubbles observed. There was no statistically significant association between the degree of mitral regurgitation and the observation of microbubbles.

Microbubbles are a common phenomenon occurring in patients with mechanical mitral prostheses compared with tissue mitral valve prostheses. Their formation depends on the systolic ventricular function, suggesting a cavitation-like phenomenon participating in their formation perhaps due to the rate or velocity of the valve closure.