The QT mandate

Though not dangerous in and of itself, QT prolongation is used as a surrogate to track the electrophysiological environment in the heart. Thus, QT prolongation must be viewed as only one, and perhaps not the best, predicate for the risk of developing a life-threatening arrhythmia.

Cardiac contractions are the result of cardiac depolarization. To maximize the force of the contraction, there is uniformity in the depolarization sequence - the atria contract, then the ventricles contract - allowing both sets to fill properly before ejecting the blood to its next destination. ...