1. Division of Cardiology; Fondazione Cardiocentro Ticino; Via Tesserete 48, CH-6900 Lugano Switzerland
2. University Medical Centre Utrecht; Utrecht The Netherlands
3. Department of Physiology; Cardiovascular Research Institute Maastricht; Maastricht The Netherlands
4. Service of Biometry and Statistics, Research Department; IRCCS Fondazione Policlinico San Matteo; Pavia Italy