Quantitation of day to day variability in mode of induction of ventricular tachyarrhythmias by programmed stimulation

AbstractSpontaneous day to day variability in the mode of induction of ventricular tachycardia at programmed stimulation in the drug-free state has been described but not quantitated. To quantitate this variability, this study employed a new protocol of programmed stimulation in which the number of extrastimuli required for tachycardia induction was the only major stimulation variable. This protocol was applied to 18 consecutive patients with previously documented sustained ventricular tachyarrhythmia due to coronary artery disease. One to seven extrastimuli were available for arrhythmia induction if required. Each patient underwent programmed stimulation in the absence of antiarrhythmic drugs on 3 separate days with a mean interval of 5 ± 2.7 days between studies.A sustained ventricular tachyarrhythmia was inducible in all studies with ≤4 extrastimuli; the mean number of extrastimuli required was 2.4 ± 0.8. Day to day variability in the number of extrastimuli required for tachycardia induction was observed in the majority of patients (72%). Eleven patients (61%) varied by one extrastimulus over the three control studies, and two patients (11%) varied by two extrastimuli. At analysis of variance, the 95% confidence interval for the degree of day to day variability was ± 1 extrastimulus from the mean number required in the three studies. Multiple configurations of induced ventricular tachycardia were frequently observed at repeat studies and occurred in 15 patients (83%).In conclusion, spontaneous day to day variability in mode of induction of ventricular tachycardia in the absence of drugs is common. The 95% confidence limit is a sizable ±1 extrastimulus from the mean, representing a variability of ± 46% of the mean value. Failure to allow for this variability will cause false estimations of antiarrhythmic drug efficacy at electrophysiologic testing