Termination of sustained ventricular tachycardia by ultrarapid subthreshold stimulation in humans.

Our purpose was to investigate the efficacy, safety, and electrophysiological mechanism of ultrarapid subthreshold electrical stimulation in terminating sustained ventricular tachycardia (VT) in humans. Fifteen patients with inducible sustained hemodynamically stable VT and whose VT cycle length ranged between 295 and 440 msec (337 +/- 60 msec) were included in this study. The stimulation threshold and ventricular myocardial effective refractory period were determined during VT, and the values ranged between 0.4 and 1.2 mA (mean, 0.7 +/- 0.3 mA) and between 185 and 245 msec (mean, 225 +/- 20 msec), respectively. Trains of ultrarapid subthreshold stimulation were delivered with cycle lengths of 100 to 10 msec in decremental steps of 10 msec. A 5-second pause was allowed between each step (decrement). A 2-msec pulse width was used in all patients, and a 4-msec pulse width was also tested in eight patients. Any apparent captured beat was disregarded. In eight (53%) patients, ultrarapid subthreshold stimulation terminated VT, and in the remaining seven (47%) patients, it did not. The lowest subthreshold stimulation that effectively terminated VT was 0.05 mA. In 10 patients, the site of early activity during VT was determined by endocardial catheter mapping, and subthreshold stimulation more effectively terminated VT in eight patients when it was applied close to the site of early activity. In seven patients who underwent mapping-guided arrhythmia surgery, subthreshold stimulation was applied close to the site of early activity and successfully terminated VT. In no patient did subthreshold stimulation produce acceleration of VT or induce ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)