1. Department of Pediatrics, Hanyang University School of Medicine, 17 Haengdang‐dong, Sungdong‐ku, Seoul 133–792, Korea,
2. Department of Cardiology, Hanyang University School of Medicine, 17 Haengdang‐dong, Sungdong‐ku, Seoul 133–792, Korea,
3. Department of Pediatrics, Seoul National University School of Medicine, 28 Yongon‐Dong, Chongno‐Ku, Seoul 110–799, Korea