Cellular Basis for the ECG Features of the LQT1 Form of the Long-QT Syndrome

This experimental model of LQT1 indicates that a deficiency of IKs alone does not induce TdP but that the addition of beta-adrenergic influence predisposes the myocardium to the development of TdP by increasing transmural dispersion of repolarization, most likely as a result of a large augmentation of residual IKs in epicardial and endocardial cells but not in M cells, in which IKs is intrinsically weak. Our data provide a mechanistic understanding of the cellular basis for the therapeutic actions of beta-adrenergic blockers in LQT1 and suggest that sodium channel block with class IB antiarrhythmic agents may be effective in suppressing TdP in LQT1, as they are in LQT2 and LQT3, as well as in acquired (drug-induced) forms of the long-QT syndrome.