1. Department of Medicine/Cardiology, West Roxbury Veterans Affairs Medical Center, Harvard Medical School, West Roxbury, Massachusetts, USA
2. Department of Medicine/Cardiology, McGuire Veterans Affairs Medical Center, Medical College of Virginia, Richmond, Virginia, USA
3. Departments of Medicine and Physiology, Medical College of Virginia, Richmond, Virginia, USA
4. Department of Pathology, University of Western Ontario, London, Ontario, Canada