- History of cardiac abnormalities, including abnormal and clinically relevant ECG changes such as bradycardia (sinus rate <45 bpm), complete left bundle branch block (LBBB), second or third degree heart block, intraventricular conduction delay with QRS duration >120 msec, symptomatic or asymptomatic arrhythmias with the exception of sinus arrhythmia, evidence of ventricular pre-excitation, frequent palpitations or syncopal episodes, heart failure, hypokalemia, family history of Long QT Syndrome, and/or family history of sudden death in an otherwise healthy individual between the ages of 1 and 30 years.