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Hydrodynamic comparison of biological prostheses during progressive valve calcification in a simulated exercise situation. An in vitro study

^a Department of Thoracic & Cardiovascular Surgery, Johann Wolfgang Goethe University Hospital, Theodor-Stern-Kai 7, 60596 Frankfurt am Main, Germany
^b Cardiovascular Engineering Group, Helmholtz Institute Aachen, Germany
^c Institute of Multiphase Processes, Leibniz University of Hannover, Germany

Received 10 December 2007; received in revised form 1 May 2008; accepted 7 May 2008.

^_* Corresponding author. Tel.: +49 69 6301 6527; fax: +49 69 6301 83279. (Email: farhad{at}bakhtiary.de).

Objective: Despite continuous development of anticalcification treatment for biological valve prostheses, calcification remains one major cause of structural failure. The following study investigates hemodynamics and changes in opening and closing kinematics in progressively calcified porcine and pericardial valves in a simulated exercise situation. Materials and methods: Five pericardial (Edwards Perimount Magna) and five porcine (Medtronic Mosaic Ultra) aortic valve bioprostheses (23 mm) were investigated in an artificial circulation system (150 beats/min, cardiac output 8 l/min). Leaflet kinematics were visualized with a high-speed camera (3000 frames/s). Valves were exposed to a calcifying solution for 6 weeks. Repeated testing was performed every week. All prostheses underwent X-ray and photographic examination including measurement of calcium content for evaluation of progressive calcification. Results: In the exercise situation pericardial valves demonstrated lower pressure gradients initially compared to the porcine valves (8.5 ± 1.4 vs 11 ± 1.6 mmHg), but significantly higher closing volume (5.3 ± 1.2 ml vs 1.2 ± 0.2 ml of stroke volume) leading to an equal total energy. Neither valve type demonstrated a significant increase in gradient or closing volume compared to the normal output situation. Opening and closing times were longer for pericardial valves after 6 weeks (opening time 42 ± 10 ms vs 28 ± 10 ms, closing time 84 ± 12 vs 52 ± 10 ms after 6 weeks). Pericardial valves calcified faster and more severely leading to an increase in gradients and closure volume. Conclusions: In the exercise situation pericardial valves demonstrated superior systolic function compared to porcine valves. Therefore pericardial valves have some advantage in active patients due to the lower gradients. Total energy loss remained constant during progressive calcification for both valves. Leaflet opening and closing is faster in porcine valves; clinical impact of these findings is not known. Diastolic performance is also important and should always be tested also in vivo.

Key Words: Aortic valve bioprosthesis • Hemodynamics • Valve durability