THE EFFECT OF INDUCING VENTRICULAR-FIBRILLATION WITH 50-HZ PACING VERSUS T-WAVE STIMULATION ON THE ABILITY TO DEFIBRILLATE

When testing an ICD, there are at least two techniques for inducing ve ntricular fibrillation: (1) high frequency (approximate to 50 Hz) paci ng; and (2) a single T wave stimulus. It is generally assumed that the se two methods yield similar results. This study directly tested this assumption. In six dogs, one defibrillation electrode was placed in th e right ventricular (RV) apex and the second was placed cutaneously on the left thorax. All defibrillation and T wave stimuli were biphasic between these two electrodes. Pacing was monophasic from the tip of th e RV catheter to the cutaneous patch. The voltage which defibrillates 50% of the time (DF50) was measured using a 10-step Bayesian up-down m ethod. Observations for two DF50 measurements were randomly interleave d. For one DF50 measurement, fibrillation was induced with 99 pacing s timuli at a 20-ms pacing interval (50-Hz pacing). For the second DF50 measurement, fibrillation was induced with a single defibrillation sho ck of approximately 1/2J delivered at a time corresponding to the peak of the T wave in the lead II electrogram (T wave stimuli). The averag e DF50 when measured after fibrillation induced with 50-Hz pacing was 379 +/- 54.6 V as compared to 382 +/- 50.3 V when fibrillation was ind uced with T wave stimuli. The difference of 3 V uas not statistically significant. if these results are confirmed in humans, it is reasonabl e to assume that the efficacy of a defibrillation shock is the same wh ether T wave stimuli or 50-Hz pacing are used to induce fibrillation.