The electrophysiological effects of alternate vs. single electrode pacing

For the purpose of evaluating the electrophysiological effects of two modes of ventricular pacing, a linear array of eleven electrodes with an intraelectrode distance of 2.5 mm was sutured to the left ventricle. The ventricle was paced with stimuli applied to one electrode (conventional pacing) located at the center of the array and two stimuli (S1S2) delivered sequentially to two electrodes (alternate mode pacing). The alternate mode pacing was examined at different intraelectrode distances from 5 to 25 mm separation. The test stimulus (S3) used to determine the effective refractory period (ERP) and ventricular fibrillation threshold (VFT) was delivered to the central electrode within the array. The ERP, conduction time, VFT, maximum capture rate and the rate which induces VP were evaluated in ten dogs. The ERP increased sharply at a distance of greater than 15 mm between S1 and S2, which is 7.5 mm from S3. Conduction time recovered at a distance of 10 mm S1S2 only 5 mm from S3. VFT and the maximum rate which induced VF, sharply increased at a distance of 15 mm, and the maximum pacing capture rate declined rapidly at this distance as well. Single electrode pacing has shown previously, and in this study, to reduce ERP, increase conduction time and increase ERP dispersion all within 15 mm from the stimulation site, thus increasing ventricular vulnerability. Alternate mode pacing with intraelectrode distance of greater than 15 mm reduced ventricular vulnerability. It doubled the recovery time of each stimulated site, increased VFT and provided protection from rapid electrical stimulation.