DIAGNOSTIC METHODS ELECTROPHYSIOLOGY Comparison of bipolar and unipolar programmed electrical stimulation for the initiation of ventricular arrhythmias: significance of anodal excitation during bipolar stimulation

To determine if anodal excitation during bipolar stimulation facilitates the initiation of sustained monomorphic ventricular tachycardia, nonsustained polymorphic ventricular tachycardia, or repetitive ventricular responses, both bipolar and cathodal unipolar programmed ventricular stimulation with one to three extrastimuli delivered during ventricular pacing at two rates from the right ventricular apex were performed in 28 patients evaluated for spontaneous sustained ventricular tachycardia or ventricular fibrillation (11 patients), nonsustained tachycardia (eight patients), or syncope (nine patients). In 25 patients a hexapolar pacing catheter was used to record local endocardial activation times adjacent to the cathode and anode and ventricular excitation during bipolar stimulation was defined as predominantly anodal, cathodal, or simultaneous at both anode and cathode. When bipolar and unipolar stimulation were compared there was no difference in the incidence of initiating sustained monomorphic ventricular tachycardia (57% vs 57%), nonsustianed polymorphic ventricular tachycardia (14% vs 14%), or repetitive ventricular responses (21% vs 2 1%), although the response to bipolar vs unipolar stimulation was not concordant in every patient. Evidence of anodal excitation was observed in 11 (44%) patients but did not indicate increased risk of initiation of any ventricular arrhythmia, despite the fact that it was associated with shortening of the ventricular effective refractory period by 5.2 8.7 msec (p < .05) during bipolar as opposed to unipolar stimulation. We conclude that unipolar and bipolar stimulation produce a similar incidence of initiation of arrhythmia, despite the frequent occurrence of anodal excitation during bipolar stimulation. Thus, the risk of initiation of nonspecific ventricular arrhythmias during programmed stimulation is unlikely to be reduced by the use of unipolar stimulation. Circulation 73, No. 4, 693-700, 1986. PROGRAMMED electrical stimulation for the purpose of initiating ventricular arrhythmias in humans is usually performed with a bipolar pair of endocardial electrodes. During bipolar pacing local myocardial excitation may begin at the cathode, the anode, or simultaneously at both sites. 2 The shorter refractory period of anodal as opposed to cathodal ventricular stimulation`A and changes in the relative contribution of cathode and anode to ventricular excitation during programmed stimulation are factors that could influence the ability of bipolar programmed stimulation to initiate ventricular arrhythmias in humans but that have received little attention. From the Department of Medicine, Division of Cardiology, UCLA School of Medicine, Los Angeles. Address for correspondence: William G. Stevenson, M.D., Division of Cardiology, UCLA, CHS 47-123, Los Angeles, CA 90024. Received Oct. 10, 1985; revision accepted Dec. 19, 1985. Vol. 73, No. 4, April 1986 To determine if anodal excitation during bipolar stimulation facilitates the initiation of either clinically important sustained monomorphic ventricular tachycardia or less specific arrhythmias, such as repetitive ventricular responses and nonsustained polymorphic ventricular tachycardia,5 we compared the initiation of these arrhythmias and the presence of anodal ventricular excitation as determined from local ventricular electrograms adjacent to the cathode and anode during bipolar and cathodal unipolar programmed stimulation in 28 patients referred for evaluation of documented or suspected ventricular arrhythmias. Methods Clinical characteristics of the patients are listed in table 1. All studies were performed in the absence of antiarrhythmic drugs and diazepam was used as needed for sedation. After informed consent was obtained from each patient two or three electrode 693 by gest on A ril 9, 2017 http://ciajournals.org/ D ow nladed from