1 Departments of Surgery and Cardiothoracic Surgery, Amsterdam UMC, VU University Medical Center, Amersterdam, The Netherlands. Electronic address: d.heineman@amsterdamumc.nl.
2 Department of Surgery, Leiden University Medical Center, Leiden, The Netherlands; Scientific Bureau, Dutch Institute for Clinical Auditing, Leiden, The Netherlands.
3 Department of Surgery, Northwest Clinics, Alkmaar, The Netherlands.