[1] Harvard Univ, Sch Med, Childrens Hosp Boston, Dept Cardiol, Boston, MA 02115 USA
[2] Harvard Univ, Sch Med, Dept Pediat, Childrens Hosp Boston, Boston, MA 02115 USA
[3] Harvard Univ, Sch Publ Hlth, Dept Biostat, Boston, MA 02115 USA
[4] Bambino Gesu Pediat Hosp, Dept Cardiol, Rome, Italy
[5] Harvard Univ, Sch Med, Childrens Hosp Boston, Dept Cardiac Surg, Boston, MA 02115 USA