1. From the Departments of Cardiac Surgery (L.F.D., I.H., T.S., L.B.M., C.S., R.A.J.) and Biostatistics (D.Z.), Children’s Hospital Boston, and Harvard Medical School, Boston, Mass., and the Department of Cardiovascular and Thoracic Surgery, University Hospitals, Homburg/Saar, Germany (H.-J.S.).