Ventricular Ectopic Rhythms and Ventricular Fibrillation Following Cardiac Sympathectomy and Coronary Occlusion

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Abstract
Upper thoracic sympathectomy prior to occlusion of the anterior descending artery of the dog reduces ectopic ventricular activity and the probability of ventricular fibrillation during the first phase (first 10 min.) following such an occlusion. The sympathectomy does not completely prevent ventricular ectopic rhythms or ventricular fibrillation during this phase. During the 2d phase (first 4.5-8hrs. following the short 1st phase) significant degrees of ectopic ventricular activity have occurred only during excitement periods while awakening following operations in which pentothal Na anesthesia was used. Few ectopic beats were recorded during this period from animals operated under ether, morphine-barbital Na, or pentobarbital Na. The episodes of ectopic ventricular activity observed during this period following occlusion under pentothal Na have failed to occur in expts. in which upper thoracic sympathectomy preceded coronary occlusion. Excitation by the sympathetic nerves probably is a major factor in the production of these ectopic beats. The maximal rates during this period are about 50/min.; therefore no danger from ectopic activity is to be anticipated during the 2d phase. Prior sympathectomy has not changed the time of onset of 3d phase activity (4.5-8 hrs.). Sympathectomy probably reduced somewhat the maximal ectopic frequencies, though ectopic rates as high as 210/min. have been recorded in sympathectomized animals. The duration of 3d phase ectopic activity appears to be shortened by sympathectomy. It is probable that the excitatory factors that produce ectopic impulses are multiple during all phases. The apparent relative contribution of the cardiac sympathetic innervation to ectopic excitation during each phase is discussed briefly.