[1] Univ Nebraska, Childrens Hosp & Med Ctr, Div Pediat Cardiol, Coll Med, Omaha, NE 68114 USA
[2] Creighton Univ, Sch Med, Childrens Hosp & Med Ctr, Omaha, NE USA
[3] Univ Alberta, Div Pediat Cardiol, Dept Pediat, Stollery Childrens Hosp, Edmonton, AB, Canada