Abstract
We studied the effects of cardiac sympathetic stimulation and ablation on characteristics of the anodal-strength interval curve in 10 pentobarbital-anesthetized open-chest dogs. We gave special attention to the 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 muA to 774 +/- 326 muA P less than 0.1). However, after left stellectomy and upper thoracic ganglionectomy, stimulation of the cut ends the ansa subclavia decreased the dip threshold from an average of 952 +/- 321 muA to 707 +/- 210 muA, A less than 0.01. Dip thresholds in strength-interval curves determined 1-1.5 hours after ganglionectomy average 1164 +/- 296 muA compared to an average dip threshold of 791 +/- 269 muA in strength-interval curves measured immediately prior to stellectomy. This increase is statistically significant (P less than 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.
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