1. Department of Cardiology, Children's Hospital Boston and Harvard Medical School, Harvard University, Boston, Massachusetts;
2. Department of Cardiology, Children's Hospital of Los Angeles and Keck School of Medicine, University of Southern California, Los Angeles, California;
3. Department of Pediatrics, Rady Children's Hospital San Diego and School of Medicine, University of California, San Diego, California; and
4. Department of Pediatrics, Children's Memorial Hospital and Feinberg School of Medicine, Northwestern University, Chicago, Illinois