ELECTROPHYSIOLOGIC EFFECTS OF ANTIARRHYTHMIC DRUG-THERAPY IN THE PREDICTION OF SUCCESSFUL SUPPRESSION OF INDUCED VENTRICULAR-TACHYCARDIA

Predictors of a successful outcome of serial electrophysiologic (EP) a nd drug studies have been identified from among baseline patient chara cteristics but not from among measures of baseline and drug-related EP effects, Identifying such predictors would be useful in explaining th e mechanism of successful drug therapy and in guiding drug development and selection. We prospectively studied EP characteristics in 159 tri als in 62 patients with ventricular tachycardia or ventricular fibrill ation during antiarrhythmic therapy and compared EP measures between s uccessful (n = 30) and failed trials (n = 129), The average age of the patients was 64 years (range 27 to 78 years); 82% were men and 18% wo men; and 87% had coronary artery disease, Measurements included R-R, Q RS, and QT intervals during intrinsic rhythm and during pacing at cycl e lengths of 600 of 400 msec; ventricular effective refractory periods (ERP) during pacing at cycle lengths of 600 and 400 msec; and changes in these measures, comparing treatment with drug-free baseline. Univa riate predictors of success (in order of significance) included ERP(60 0)/QRS(600), sotalol versus other drugs, ERP(400)/QRS(400), Delta ERP( 600), Delta R-R, ERP(600), QRS(400) (negative association), Delta ERP( 400), QRS(600), (negative association), ERP(400) (all p < 0.1), In two separate multivariate models, one for each drive cycle length, only t he ratio ERP(600)/QRS(600) (p = 0.01) in the first model and ERP(400)/ QRS(400) (p = 0.01) in the second model were significantly and indepen dently associated with achieving noninducibility with drug therapy, Th erefore measures of greater refractoriness and lesser delays in conduc tion velocity tie, greater ''wavelength'') relate to drug success, The se observations may assist in new drug development and, with other pre dictors, in drug selection for the treatment of patients.