QT Interval Revisited —Not Just the Matter of “Interval,” but “Dynamics, Variability and Morphology” Matter!—

Recently, the effects of QT interval prolongation have received more attention among clinicians, industry, and official regulatory agencies. Some have advocated the total elimination or discontinuing development of drugs which prolong the QT interval. In this review, we will give a brief overview of the pathophysiology and the dynamic variability and morphology of the QT interval. From the view point of arrhythmogenesis, QT interval prolongation with increased heterogeneity of ventricular repolarization is critical. The problem is how to detect such an abnormal repolarization. To detect heterogeneity, a new index should be developed and validated, and it must incorporate QT variability and morphology of the T wave. The heart rate correction of the QT interval is also an important issue, and disclosing conflict‐corrected QT intervals depend on the formulae used. Not just QT interval prolongation is important; what also matters is the heterogeneity of ventricular repolarization.