1. Department of Internal Medicine, Päijät-Häme Central Hospital, Lahti, Finland
2. Electrophysiology Section, Division of Cardiology, University of California, San Francisco
3. Division of Cardiology, Heart and Lung Center, Helsinki University Hospital, Helsinki, Finland
4. Research Unit of Internal Medicine, Medical Research Center, Oulu University Hospital and University of Oulu, Oulu, Finland
5. The National Institute for Health and Welfare, Helsinki, Finland
6. Department of Epidemiology and Biostatistics, University of California, San Francisco