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