[Doppler and valvular prostheses].

Abstract

The principle of examination of prosthetic valves is not different from that of the original valves in terms of bioprosthesis. On the contrary, mechanical prosthesis are markedly opaque to ultrasounds and cause masking and non-flow phenomena behind the prosthesis, which are capable to completely hide abnormal retrograde flows, in traditional views (Apical 4 cavities to demonstrate a mitral leakage). Therefore, with mechanical prostheses, it is necessary to "cheat" and use atypical views which avoid interposition of the prosthesis between the ultrasound beam and the abnormal flow. The function of the prosthesis is evaluated on the following parameters: maximum transprosthetic velocity, maximum instant gradient, mean gradient and functional prosthetic area derived either from T1/2 or from the application of the continuity equation. The main factors of transprosthetic Max. V and gradients are the type and size of the prosthesis, the age of the prosthesis is only a factor for bioprostheses, and the cardiac rate and output. The golden rule is therefore to record, one month after the procedure, the Doppler characteristics of any new prosthesis, the patient being his own reference, year after year. Finally the characteristic manifestations of various dysfunctions are presented.