Pulsatile flow testing of heart valve prostheses in vitro

Abstract

For the approval-relevant testing to prove the safety and effectiveness of newly developed heart valve prostheses, a new version of the ISO 5840-family was published in 2021. One of the major in vitro tests in this standard is the investigation of the hydrodynamic performance of heart valve prostheses by means of a hydrodynamic cardiovascular test bench (pulse duplicator system). A new requirement of the ISO 5840:2021 is the validation of the pulse duplicator system used, by comparing the results obtained with the test bench with a round-robin study published by the ISO Cardiac Valves Working Group in 2019. In this work, two pulse duplicator systems at our institute (2x BDC Laboratories, Wheat Ridge, CO, USA) were evaluated according to the new ISO standard. The results obtained were compared intra-institutionally between the different test benches and internationally with the round-robin study to validate the developed test methodology regarding the normative requirements. For the evaluation and to assess the repeatability, one measurement series with three measurements was performed for the intra-institutional comparison, a second measurement series with eight measurements with different parameters was conducted for the inter-laboratory comparison. The test parameters were selected according to the round-robin study. A mechanical prosthetic heart valve (St. Jude Medical Master Series, diameter: 25 mm) was used as test valve. The values for the effective orifice area (EOA) and the regurgitant fraction (RF) were assessed, and the pressure and flow waveforms were analysed. In general, the developed and applied test methods lead to reliable results according to ISO 5840:2021 and compared to the international standard in different test laboratories. Both BDC pulse duplicators have achieved reliable results in terms of repeatability in the intra-institutional and inter-laboratory comparison. The test benches are therefore suitable for the hydrodynamic performance testing of heart valve prostheses according to ISO 5840:2021. During the experiments slightly higher EOA and RF were measured by means of one pulse duplicator system although both test benches were identical. High-speed cinematography recordings identified an asymmetric closing kinematic of the test valve. Thus, leading to a prolonged closing time and closing volume of the valve. This in turn, led to an increased EOA, due to the calculation according to the ISO standard. In conclusion, even small deviations in the closing kinematics of the test valve can lead to large differences in the results. Thus, it is considered to attach great importance to the leaflet kinematics when comparing or validating test benches or test methods.