1. From the Divisions of Cardiovascular Diseases (D.B.S., P.J.P., M.S., D.R.H., B.J.G., C.S.R., R.D.S., R.G.) and Biomedical Statistics and Informatics (R.J.L.), Mayo Clinic, Rochester, MN; and Division of Cardiovascular Diseases (I.D.M.), Mayo Clinic, Jacksonville, FL.