Prosthesis-Annulus-Relation (PAR) as predictor of hemodynamic outcome in aortic valve replacement – rationale of the PAR I trial

Great debates revolve around the hemodynamic performance of prosthetic tissue valves. It is influenced by the design and the specific sizing strategy. Design determines the actual geometric opening area of the valve (GOA), sizing strategy the actual size of the selected valve. Currently, hemodynamic performance is generally assessed by determining the effective orifice area (EOA, derived from the continuity equation by relating flow velocities and LVOTarea). The question whether a valve is too small (patient-prosthesis-mismatch, PPM) is then addressed by relating EOA to body surface area (EOAi). However, this relation may not be reasonable because the EOAi relates flow velocity to patient-specific anatomic parameters (LVOTarea and body surface area) twice. Considering this potential methodological flaw, debate and confusion regarding PPM is easily understood, despite the fact that, intuitively, leaving a gradient behind after aortic valve replacement cannot be irrelevant. PPM becomes even more relevant in times of valve-in-valve transcatheter implantation, where a second prosthesis is taking up inner space of a valve that may have been too small in the first place. Thus, a reliable and comparable method to determine the presence of PPM is needed. The Prosthesis -to-Annulus Relation (PAR I) trial is a German multicenter study assessing the relation between the true prosthetic GOA and the LVOTarea as potentially new parameter for the prediction of hemodynamic outcome, to possibly guide future valve size selection (incl. valve-in-valve) and to allow the detection of functionally relevant PPM. We will demonstrate the shortcomings of the currently applied EOAi for assessment of hemodynamic relevance and present the rationale for the PAR I trial. The trial recently started recruiting patients and will assess in 300 conventional aortic valve replacements how the anatomic dimensions of patients and implanted valves relate to each other and whether they allow the prediction of hemodynamic outcome.