Electrophysiology of postinfarction ventricular tachycardia: a paradigm of stable reentry.

Sustained monomorphic ventricular tachycardia (VT) is a paradigm of a stable reentrant rhythm. The hallmark of stable reentry is the presence of an excitable gap, which in reentrant VT composes 15% to 45% of the tachycardia cycle length. Resetting allows definition of the extent and pattern of the excitable gap. Site-specific resetting responses suggest that the VT circuit has both functionally and anatomically derived characteristics. Entrainment provides information regarding the effects of overdrive pacing on properties of the tissue composing the circuit rather than on properties of the tachycardia itself. These data help us to understand the mechanisms of pharmacologic agents and to direct ablation of reentrant VT.