Ultrarapid single-capture train stimulation for termination of ventricular tachycardia.

Termination of ventricular tachycardia (VT) with single programmed extrastimuli or slow underdrive competitive pacing is often possible. The usefulness of these techniques is limited because the zone in the cardiac cycle during which programmed stimuli are effective may be narrow, with significant time elapsing until termination of the VT, and the zone may vary markedly between episodes, rendering preset extrastimuli ineffective. Ultrarapid trains of stimuli beginning during the refractory period and of a duration sufficient to cause only a single capture should terminate all tachycardias whose termination zone begins just after the refractory period. To test this hypothesis, 21 patients with 371 well-tolerated episodes of VT had single programmed extrastimuli and trains of 10 bipolar stimuli at 25, 50, and 100 Hz. VT was terminated 1 or more times in 18 of the 21 patients with programmed extrastimuli or trains, or both. Forty-eight percent of 290 episodes were terminated with programmed stimulation, compared with 56% of 120 episodes with trains (difference not significant). In 98 episodes, the effects of trains and programmed stimulation could be matched (same patient, date, tachycardia morphology, rate, and drug therapy); the results were concordant (both techniques either terminated the VT or failed) in 92 and discordant in 6. With only 2 possible exceptions, the termination zone always began just after the refractory period; thus, for tachycardias terminating with single captures, the first train to achieve capture was effective, minimizing the duration of the VT.