1. From the Cardiovascular Division (S.D.S., P.J., E.B., M.A.P.), Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass; the National Heart, Lung, and Blood Institute (M.D.), Bethesda, Md; the George Washington University Biostatistics Center (M.M.R., K.A.J.), Rockville, Md; the University of Montreal (J.L.R.), Montreal, Quebec, Canada; and the Mayo College of Medicine (B.J.G.), Rochester, Minn.