Mechanisms of resetting reentrant circuits in canine ventricular tachycardia.

BACKGROUND Resetting has been used to characterize reentrant circuits causing clinical tachycardias. METHODS AND RESULTS To determine the mechanisms of resetting, sustained ventricular tachycardia was induced in dogs with 4-day-old myocardial infarctions by programmed stimulation. Premature stimulation was accomplished from multiple regions within reentrant circuits; resetting curves were constructed and compared with activation maps. Monotonically increasing responses, or a "mixed" response (increasing portion preceded by a flat portion), occurred. All reentrant circuits had a fully excitable gap. Interval-dependent conduction delay and concealed retrograde penetration led to increased resetting response curves. CONCLUSIONS Multiple mechanisms revealed by mapping cause resetting of reentrant circuits.