Assessment of the opening angle of implanted Björk-Shiley prosthetic valves

A method has been developed in which cineradiography is used for the assessment of the opening angle of implanted Bjork-Shiley prosthetic valves. The method is based on the fact that the ring and the disc, which are known to be circular, appear to be elliptical on x-ray films. The spatial position of the valve can be retrieved from the characteristics of these ellipses when vectoranalysis is applied. The method's accuracy does not depend on the position of the patient with respect to the direction of the x-ray beam. The accuracy of the method was demonstrated with the use of a phantom valve. The difference between the measured and the real opening angle was -0.7 +/- 1.8 degrees (mean +/- SD). Results were reproducible in patients to within -0.1 +/- 1.8 degrees. In 18 patients with normally functioning valves it could be demonstrated with frame-by-frame analysis (interval between frames 20 msec) that the valves opened very rapidly up to about 60 degrees. Closing patterns varied. In one of our patients with valvular thrombosis insufficient valvular opening could be demonstrated by our method before the patient's complaints drew attention to the valvular dysfunction.