Autonomic Nerve Stimulation Reverses Ventricular Repolarization Sequence in Rabbit Hearts

Sympathetic activity and spatial dispersion of repolarization (DOR) have been implicated as mechanisms that promote arrhythmia vulnerability; yet there are no direct measurements of the effects of autonomic nerve stimulation on DOR. Rabbit hearts were perfused in a Langendorff apparatus with full sympathetic and parasympathetic innervation and were optically mapped to measure action potential durations and DOR (apex-base) over the left ventricles. DOR was measured under sinus rhythm, during bilateral sympathetic nerve stimulation (SNS) and right and/or left vagus nerve stimulation and was compared with DOR during isoproterenol (100 nmol/L) or acetylcholine (1 micromol/L) infusion. In sinus rhythm, repolarization started at the apex and systematically progressed toward the base. SNS (10 to 15 Hz) increased DOR by 29% (from Deltaaction potential duration=17+/-0.7 to -22+/-1.6 ms, n=6) and reversed DOR as the direction of repolarization from apex-->base in sinus rhythm shifted to base-->apex in 5 to 15 seconds after SNS. DOR flipped back to its sinus rhythm DOR pattern 115+/-15 seconds after the interruption of SNS. During right or left vagus nerve stimulation, there was no change in the direction of DOR, but bilateral vagus nerve stimulation increased and reversed DOR to base-->apex direction. Infusion of isoproterenol or acetylcholine increased DOR but did not alter the direction of repolarization sequences. These findings demonstrate that bilateral autonomic activity (SNS or vagus nerve stimulation) cause reversible shifts of apex-base DOR and that the spatial heterogeneities of autonomic effects on the ventricles are most likely attributable to a greater innervation at the base than the apex of the heart.