1. From Johns Hopkins Hospital, Departments of Medicine/Cardiology (S.N., D.A.B., A.C.L., M.M.Z., S.P.W., T.L.D., G.R.M., A.R., H.C., G.F.T., R.G.W., R.D.B., J.A.C.L., H.R.H.), Radiology (D.A.B, J.A.C.L., H.R.H.), Biomedical Engineering (A.C.L., H.R.H.), and Surgery (A.C.L.), Baltimore, Md.