1. Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
2. Department of Anesthesiology and Critical Care, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
3. Department of Anesthesiology, Yale University, New Haven, Connecticut
4. Division of Cardiovascular Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
5. Division of Cardiothoracic Surgery, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
6. Division of Cardiovascular Medicine, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania
7. Division of Cardiovascular Medicine, University of Utah Hospital, Salt Lake City, Utah.