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.