1. Department of Medicine and Therapeutics, Gardiner Institute, Western Infirmary, Glasgow G11 6NT, Scotland, U.K.
2. Department of Cardiothoracic Surgery, Western Infirmary, Glasgow G11 6NT, Scotland, U.K.
3. Service Cardiovasculaire, Hôpital Broussais, 96 rue Didot, F-75674 Paris cedex 14, France