Oliver J Liakopoulos1, Yeong-Hoon Choi2. 1. Department of Cardiothoracic Surgery, Heart Center, University of Cologne, Cologne, Germany; Department of Cardiac Surgery, Kerckhoff Clinic Bad Nauheim, Campus Kerckhoff, University of Giessen, Germany. Electronic address: oliver@liakopoulos.de. 2. Department of Cardiac Surgery, Kerckhoff Clinic Bad Nauheim, Campus Kerckhoff, University of Giessen, Germany.