ELECTROPHYSIOLOGIC EFFECTS AND PREDICTORS OF SUCCESS OF COMBINATION THERAPY WITH CLASS IA AND IB ANTIARRHYTHMIC DRUGS FOR SUSTAINED VENTRICULAR ARRHYTHMIAS

Antiarrhythmic drugs remain the first line of therapy in patients with sustained ventricular arrhythmias, Although success with class la ant iarrhythmic medications has been limited, there is evidence that the a ddition of a class 1b agent may improve results. A total of 110 consec utive patients referred for electrophysiologic evaluation who had indu cible sustained ventricular arrhythmias resistant to a class 1a agent underwent repeat electrophysiologic study after the addition of a clas s Ib drug. Patients with election fraction >40% and ventricular fibril lation inducible in the baseline study had an 80% response rate, where as those with inducible ventricular tachycardia and ejection fraction less than or equal to 40% responded 11% of the time. Responders demons trated marked prolongation of ventricular refractoriness and slight sh ortening of the QRS, whereas nonresponders held QRS prolongation and a more modest increase in ventricular refractoriness. Thus, the efficac y of class 1a/1b combination therapy in patients with inducible sustai ned ventricular arrhythmias refractory to a class la drugs alone can b e predicted by baseline variables, Marked prolongation of ventricular refractoriness in the absence of QRS prolongation appears to be a key factor in the success of this combination.