Influence of a third extrastimulus in defining effective drug therapy during serial electrophysiological testing

Many electrophysiology laboratories use three extrastimuli in all patients with ventricular tachyarrhythmias during antiarrhythmic drug testing, regardless of the mode of arrhythmia induction in the baseline state. The purpose of this study was to compare this pacing protocol (full protocol) with a protocol in which three extrastimuli were only used during drug tests, if they were required in the baseline state for arrhythmia induction (limited protocol). There were 181 electrophysiology tests performed on 69 patients with ventricular tachyarrhythmias that were retrospectively analyzed. In all studies the full protocol was used, but the results of stimulation were also analyzed assuming the limited protocol had been used. In the baseline state, sustained ventricular tachyarrhythmias were reproducibly inducible with one or two extrastimuli in 38 (55%) patients. Of these patients, six (16%) achieved a drug efficacy prediction using the full protocol versus 15 (39%) patients using the limited protocol (P < 0.001). In all 69 patients, the drug response rate increased from 25% to 38% (P < 0.01) using the limited protocol.(ABSTRACT TRUNCATED AT 250 WORDS)