 - Corrected QT interval using Bazetts formula QTcB more than 450 milliseconds msec or QTcB more than 480 msec in subjects with Bundle Branch Block. The QTcB should be based on single QTcB values of ECG obtained over a brief recording period. If QTcB is outside the threshold value, triplicate ECGs may be performed with the QTcB values averaged. 