Torsade de pointes and other pause-induced ventricular tachycardias: the short-long-short sequence and early afterdepolarizations.

The early afterdepolarization, which is an interruption of repolarization, can evoke a second upstroke or a salvo of action potentials. It is suggested that the electrophysiological characteristics of the early afterdepolarization can produce a lengthening of the QT interval and that the second upstroke and salvo of activity that may follow, it can explain many features of torsade de pointes and of certain other ventricular tachycardias. The early afterdepolarization, torsade de pointes, and repetitive monomorphic idiopathic ventricular tachycardia are all induced by bradycardia or by a preceding long RR interal. The R-on-T phenomenon is also discussed.