Programmable polarity: effects on pacing and sensing of bipolar steroid-eluting leads

Presently available bipolar pacemakers connected to bipolar leads allow the programming of polarity to either bipolar or unipolar configuration. The bipolar configuration improves sensing because of its lack of oversensing. In respect to the pacing impulse, it may be beneficial to program the bipolar to unipolar configuration, because the unipolar pacing configuration seems to lead to lower pacing thresholds. The aim of the study was to investigate the effects of the two configurations on pacing and sensing in 11 patients with a new ventricular steroid-eluting lead (Encor Dec 033-301, Telectronics Inc.) connected to the same types of VVI(R) pacemakers. Follow-up was 12 months after implantation. Pacing was assessed by pulse duration thresholds at 0.8- 1.6-, and 2.5-V pulse amplitude and by pacing impedance. Parameters for sensing included sensing thresholds, R wave amplitudes, and amplitude of intrinsic deflection. Pulse duration thresholds were similar for the two configurations. At implantation, pacing impedance was significantly higher with bipolar (672 +/- 60 omega) than with unipolar pacing configuration (626 +/- 82 omega, P < 0.005). The difference lasted until 1 month after implantation (bipolar: 670 +/- 49 omega; unipolar: 63053 omega, P < 0.01). No significant differences were detected after 3 (bipolar: 683 +/- 63 omega; unipolar: 662 +/- 70 omega) and 12 months (bipolar: 658 +/- 64 omega; unipolar: 660 +/- 63 omega) between the 2 configurations. Although intrinsic deflections of ventricular electrograms were different, mean R wave amplitudes were similar in unipolar and bipolar configuration. Pacing and sensing characteristics of unipolar and bipolar configuration were similar for the studied bipolar pacing lead. Pacing impedance was initially higher for bipolar than for unipolar configuration and equilibrated within 3 months after implantation.