1. Cardiology Division, Arrhythmia Service, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114-2750, USA
2. Semmelweis University, Heart and Vascular Center, Városmajor 68, 1122 Budapest, Hungary
3. 1st Department of Cardiology, Medical University of Warsaw, Banacha 1a, 02-097 Warsaw, Poland
4. Lund University, Skane University Hospital, Department of Clinical Sciences Lund, Cardiology, Lund, Sweden