Effects of Cardiac Sympathetic Stimulation and Ablation on Canine Ventricular Anodal Strength-Interval Curves

We studied the effects of cardiac sympathetic stimulation and ablation on characteristics of the anodal-strength interval curve in 10 pentobarbital-anesthetized open-cbest dogs. We gave special attention to (he form and particularly the depth of early dips of the anodal strength-interval curve. When the central connections of the cardiac sympathetic nerves were intact, left stellate stimulation decreased threshold for excitation during the dip only slightly (from 883 ± 442 MA to 774 ± 326 MA, P < 0.1). However, after left stellectomy and upper thoracic ganglionectomy, stimulation of the cut ends of the ansa subclavia decreased the dip threshold from an average of 952 ± 321 UA to 707 ± 210 ̂ A, P < 0.01. Dip thresholds in strength-interval curves determined 1-1.5 hours after ganglionectomy averaged 1164 ± 296 fi\ compared to an average dip threshold of 791 ± 269 pA in strength-interval curves measured immediately prior to stellectomy. This increase is statistically significant (P < 0.005). In addition to the effects of sympathetic tone on disparity of refractory period and ventricular fibrillation threshold, the effects of sympathetic tone on the form of the strength-interval curve may be another factor influencing vulnerability to arrhythmias and particularly in patients with abnormal autonomic tone.