COMPARISON OF NUMBER OF EXTRASTIMULI VERSUS CHANGE IN BASIC CYCLE LENGTH FOR INDUCTION OF VENTRICULAR-TACHYCARDIA BY PROGRAMMED VENTRICULARSTIMULATION

Objectives. The purpose of this study was to examine the effects of va rying basic cycle lengths in a programmed stimulation protocol if up t o seven extrastimuli were available at each basic cycle length. Backgr ound. There is no uniformly accepted protocol for induction of ventric ular tachycardia. Most protocols limit the number of extrastimuli to t wo or three but use several basic cycle lengths. Methods. Twenty-eight patients with coronary artery disease and documented spontaneous sust ained ventricular tachycardia or ventricular fibrillation were studied . In the absence of antiarrhythmic drugs, each patient underwent three inductions of ventricular tachycardia/ventricular fibrillation using sinus rhythm or right ventricular pacing at 600 or 400 ms as the basic cycle length. Up to seven extrastimuli were allowed at each basic cyc le length. Results. The maximal yield of clinical tachycardia (96 %) w as identical for each basic cycle length and was achieved using a maxi mum of seven, five and four extrastimuli for sinus rhythm and 600 and 400 ms, respectively. A basic cycle length of 400 ms required fewer ex trastimuli (2.4 +/- 0.7) to induce ventricular tachycardia/ventricular fibrillation than did 600 ms (2.7 +/- 1.1, p = 0.014) or sinus rhythm (3.4 +/- 1.2, p < 0.001). There was no significant difference in the cycle lengths of the induced ventricular tachycardia, incidence of ind uced ventricular fibrillation or requirement for direct current counte rshock. Conclusions. The use of an adequate number of extrastimuli obv iates the need for multiple basic cycle lengths for induction of ventr icular tachycardia and does not increase induction of unwanted ventric ular fibrillation. If only one basic cycle length is used, the ease of inducibility can be quantified in terms of the number of extrastimuli required. Fewer extrastimuli were required for induction of ventricul ar tachycardia if a basic cycle length of 400 ms was used. These data favor the use of ventricular pacing at a basic cycle length of 400 ms with up to at least four extrastimuli as the standard stimulation prot ocol for induction of ventricular tachycardia.