THE ELECTRO-PHYSIOLOGICAL EFFECTS OF ALTERNATE VS SINGLE ELECTRODE PACING

To evaluate the electrophysiological effects of 2 modes of ventricular pacing, a linear array of 11 electrodes with an intraelectrode distance of 2.5 mm was sutured to the left ventricle. The ventricle was paced with stimuli applied to 1 electrode (conventional pacing) located at the center of the array and 2 stimuli (S1S2) delivered sequentially to 2 electrodes (alternate mode pacing). The alternate mode pacing was examined at different intraelectrode distances from 5-25 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 VF were evaluated in 10 dogs. The ERP increased sharply at a distance of > 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. Single electrode pacing reduces ERP, increases conduction time and increases ERP dispersion within 15 mm from the stimulation site, increasing ventricular vulnerability. Alternate mode pacing with intraelectrode distance of > 15 mm reduced ventricular vulnerability. It doubled the recovery time of each stimulated site, increased VFT and provided protection from rapid electrical stimulation.