Background: Myocardial depolarization can be achieved with currents of either anodal or cathodal polarity. In contrast to conventional cathodal pacing, anodal pacing initially hyperpolarizes tissue and improves myocardial contractility in animal models.
Methods and Results: In 13 patients undergoing cardiac resynchronization therapy (CRT) device implantation, we compared the mean left ventricular outflow velocity-time integral (LV-VTI) for anodal and cathodal polarities in three different pacing configurations. Intraoperative continuous-wave Doppler measurements were taken at a fixed interrogation angle, while polarities were switched during unipolar left ventricular, unipolar biventricular, and shared-coil biventricular pacing. Comparisons used identical pacing rates, intervals, and stimulus strengths. Patients had a mean ejection fraction of 0.18 ± 0.08 and a mean QRS duration of 140 ± 34 ms. All capture thresholds were less than 4.5 volts at a pulse width of 0.4 ms. Data were suitable for analysis in 37 of the 39 pairs of Doppler measurements. Anodal polarity significantly increased average LV-VTI in 36 of these 37 comparisons. The mean increase in LV-VTI for each configuration with anodal versus cathodal polarity was 2.8 ± 2.6 cm (P < 0.001). The combined mean LV-VTI for all configurations was similarly higher for anodal polarity (24.4 ± 11.7 cm) versus cathodal polarity (21.7 ± 10.9 cm; P < 0.001).
Conclusion: Anodal pacing polarity significantly improves a measure of LV function compared to traditional cathodal currents. Anodal pacing, which can be achieved by a simple reversal of pacing circuit polarity, may represent an important therapeutic addition to future resynchronization devices.