1. New England Heart and Vascular Institute, Catholic Medical Center, Manchester, NH (D.Q.).
2. Department of Medicine, Lowell General Hospital, Lowell, MA (A.F.).
3. Medtronic Inc. Mounds View, MN (J.M., M.B.).
4. Yale School of Medicine, New Haven CT (R.L.).
5. The Christ Hospital, Cincinnati OH (E.J.S.).
6. Medtronic, Inc, Minneapolis, MN (M.N.).
7. Cardiac Arrhythmia Service, Massachusetts General Hospital, Boston, MA (T.M.).