199 Unipolar vs Bipolar pacing for ventricular tachycardia pace-mapping: Does it make a difference?

Abstract

Bipolar (BI) pacing is commonly used for pace-mapping during VT ablation although the potential for capture at the proximal ring electrode can reduce accuracy. BI pacing with 2 mm interelectrode spacing has not been compared to unipolar (UNI) pacing in scared ventricular myocardium. Nineteen pts (18 M, 63 ±12 yo, LVEF: 33 ±12%) referred for scar-related VT ablation were studied. Both UNI and BI pacing (random order) were performed at the same site; at normal ventricular voltage areas (>1.5mV), at areas with voltage between 1.5 and 0.5 mV and at low voltage (<0.5mV) areas. BI pacing was performed between the 2 distal electrodes of the ablation catheter. UNI pacing was performed betweeen the distal electrode of the ablation catheter and an electrode in the IVC. Output was 10 mA for 2 ms and then decreased until threshold (TSD). QRS morphology, QRS duration and S-QRS duration were collected and analyzed off-line. To compare QRS morphology, we used the Template Matching software (Bard Electrophysiology). We performed pacing at 19 sites with voltage > 1.5 mV, 35 sites with voltage between 0.5 and 1.5 mV and 71 sites with voltage < 0.5mV. In voltage area > 1.5 mV, there was no statistical difference in term of S-QRS duration, QRS duration and morphology when pacing UNI vs BI or pacing at 10 mA and 2 msec vs threshold. Where voltage area were < 0.5 mV, S-QRS and QRS duration were shorter, when pacing at 10 mA compared to TSD in BI pacing as well as UNI pacing mode. But there was no difference comparing the 2 pacing modes at the same output. Differences in QRS morphology did occur when reducing the output to TSD (in both pacing mode). QRS morphologies were significantly different (<90% of similarity) in 29% of the sites <0.5 mV. For mapping purposes in areas of scar, close spaced bipolar pacing produces similar findings to unipolar pacing. With either pacing mode, the stimulus strength does influence QRS morphology and S-QRS delays.