EFFECT OF ISOPROTERENOL ON QRS COMPLEX MORPHOLOGY DURING VENTRICULAR PACING - IMPLICATIONS FOR PACE MAPPING

Ventricular pace mapping may be used to identify the site of origin id iopathic ventricular tachycardia. Isoproterenol is often required to i nduce this type of ventricular tachycardia. but its effect on QRS morp hology during pace mapping is unknown. Therefore, this study was perfo rmed to evaluate the effect of isoproterenol on QRS morphology during ventricular pacing. The study population consisted of 20 patients (mea n age 38 +/- 14 years) undergoing a clinically indicated electrophysio logy procedure. Ventricular overdrive pacing was performed in trains o f 12 stimuli at cycle lengths of 400, 350, 300 and 250 ms, first in th e baseline slate during an infusion of isoproterenol, and again after isoproterenol washout. Pacing was performed at the right ventricular a pex in 10 patients, in the right ventricular outflow tract in 6 patien ts, and in the left ventricle in 4 patients. Visual evaluation reveale d no apparent effects of isoproterenol on QRS morphology at any of the three pacing sites or at any of the pacing cycle lengths. Ir was conc luded that QRS morphology during ventricular pacing is not affected by isoproterenol infusion. Therefore, in patients with idiopathic ventri cular tachycardia, even if the induction of tachycardia requires infus ion of isoproterenol, successful pace mapping may be performed in its absence.