DIAGNOSTIC METHODS PROSTHETIC VALVE FUNCTION Assessment of the opening angle of implanted Bjork-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. Circulation 68, No. 2, 355-359, 1983. CONTROL of the performance of implanted prosthetic valves can be useful for proper patient management as well as for the study of factors governing prosthetic valve opening and closure. In the past, noninvasive diagnostic imaging techniques such as echocardiographylA or cineradiography5-I have been used for this purpose. Echocardiography permits some visualization of disc motion: reflections of ultrasonic waves against the disc can be recorded. Accurate assessment of the opening angle by means of application of ultrasound, however, is not yet possible. Radiologic methods for the assessment of prosthetic valvular opening, advocated until recently, need very specific patient positioning in order to hit the ring of the prosthesis tangentially. Due to the tilting movements of the atrioventricular groove, which can be 10 to 15 degrees during a cardiac cycle, in a majority of cases it is not possible to maintain a tangential beam direction for a full cardiac cycle. This can also happen in patients with aortic implants. A method resembling the one presented here has been described,8 but no data were presented about the accuracy of the method. EsFrom the Department of Cardiology, University Hospital, Utrecht, The Netherlands. Address for correspondence: Tjeerd van der Werf, M.D., Department of Cardiology, University Hospital, P.O. Box 16250, 3500 CG Utrecht, The Netherlands. Received Dec. 10, 1982; revision accepted April 7, 1983. Vol. 68, No. 2, August 1983 pecially if films of one projection only are available (see figure 2, bottom x-ray image), estimation of the short axis and the corresponding opening angle may lead to errors. We developed a method to assess opening and closing characteristics of Bjork-Shiley disc valves for each frame of a cineradiographic run, independent of the position of the patient with respect to the direction of the x-ray beam. This method is based on the fact that projections of circular objects such as the ring and the disc of the implant are, in an arbitrary spatial position, ellipsoidal and that the spatial orientation of the valve can be retrieved from the characteristics of these projected ellipses when vectoranalysis is applied. This method will be discussed and some preliminary results that show good reproducibility and accuracy -and have important clinical implications will be presented.