A comparison of QRS complexes resulting from unipolar and bipolar pacing: implications for pace-mapping.

UNLABELLED To examine differences in QRS configuration produced by bipolar versus unipolar pacing, 12-lead electrocardiograms recorded during bipolar (distal cathode) pacing with 5- and 10-mm interelectrode distances were compared to electrocardiograms recorded during unipolar cathodal pacing from the distal catheter pole. Pacing was performed at a cycle length of 500 msec using each of the two bipolar configurations at current strengths equal to late diastolic threshold, twice threshold and 10 mA. The pacing site was at the right ventricular apex in 15 patients and at various left ventricular locations in 14 patients. The electrocardiograms recorded during bipolar and unipolar pacing were compared by two independent observers for minor QRS configuration changes, major configuration changes and amplitude changes. Minor configuration differences between unipolar and bipolar pacing occurred occasionally when the interelectrode distance during bipolar pacing was 5 mm (mean +/- S.D. 0.5 +/- 1.2 leads per electrocardiogram). However, when the interelectrode distance was 10 mm, minor configuration differences were seen more commonly (1.3 +/- 2.0 leads per electrocardiogram; P less than 0.05 vs 5-mm distance). Major configuration differences were uncommon with either configuration at all current strengths. Pacing at 10 mA produced a larger number of configuration differences than pacing at either threshold or twice threshold (P less than 0.05). Amplitude differences were seen in a mean of 1.9 +/- 2.1 leads per electrocardiogram with the 5-mm interelectrode distance and a mean of 2.9 +/- 2.1 leads using the 10-mm interelectrode distance (P less than 0.05). IN CONCLUSION (1) bipolar ventricular pacing can result in QRS complexes that are different from those obtained with unipolar pacing at the same catheter location, presumably due to an anodal contribution during bipolar pacing; (2) increasing the interelectrode distance and stimulus intensity increases these differences; and (3) because the proximal electrode's contribution to depolarization can alter the QRS configuration during pacing in a variable way, the use of bipolar pace-mapping to localize sites of origin of ventricular tachycardia may result in less spatial resolution than unipolar pace-mapping.