1. From the Department of Cardiology (C.S.A., K.G., R.R.T., G.E.P., E.D.B., L.B.S., T.P.S.), Department of Cardiac Surgery (F.F.-T.), and Pediatric Transplant Center (C.S.A., E.D.B., L.B.S., F.F.-T., T.P.S.), Children’s Hospital Boston; Departments of Pediatrics (C.S.A., R.R.T., E.D.B., L.B.S., T.P.S.) and Surgery (F.F.-T.), Harvard Medical School; and Department of Biostatistics (K.G.), Harvard School of Public Health, Boston, Mass.