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Role of QT prolongation secondary to a postextrasystolic pause as a possible mechanism for the induction of ventricular fibrillation. Report of two cases.

Two patients developed ventricular fibrillation (VF) while undergoing continuous electrocardiographic monitoring. Analysis showed that VF appeared only when a particular combination of circumstances occurred: a postextrasystolic pause, QT prolongation of the subsequent beat and a premature ventricular beat that did not have a short coupling interval. The relevance of this sequence as a trigger mechanism of VF is discussed.