Distribution of sympathetic fibers in the left ventricular epicardial plexus of the dog.

Myocardial contractile force in five areas of the left ventricle was measured in 14 dogs under chloralose anesthesia prior to and following segmental chemical epicardiectomy. Electrical stimulation of the stellate ganglia was performed before and after each segment of epicardium was destroyed, and records of myocardial contractile response to stimulation were obtained. Epi-cardiectomy resulted in ablation of contractile response in specific areas of the left ventricle. In a recent publication from our laboratory (Circulation Res. 22: 315, 1968), the predominance of an epicardial distribution of sympathetic fibers was demonstrated. As an extension of that work, this study demonstrates the projection of fibers from both left and right stellate ganglia and the inner-vation of both anterior and posterior surfaces of the left ventricle. The major projections of sympathetic fibers are oriented along an axis passing from base to apex and can be interrupted by epicardial destruction in the area of the cephalad portion of the anterior descending coronary artery and adjacent to the origin of the left marginal artery. ADDITIONAL KEY WORDS myocardial' contractile force epicardiectomy stellate ganglia stimulation • There is evidence to suggest a specific regional distribution of sympathetic nerves to the heart (1). Stimulation of specific mediastinal sympathetic fibers resulted in a predictable localized inotropic response, and removal of the epicardium from small areas altered the contractile response of ventricular muscle to sympathetic nerve stimulation. Randall et al. (2) have demonstrated that a major fraction of the efferent sympathetic cardiac nerves to the anterior cardiac surface traverses the epicardial plexus en route to their terminations. Using a technique of chemical epicardiectomy, we have mapped the projections of these nerves through the epicardium enveloping the left ventricle. Analysis of the data obtained now permits us to extend the work of Randall et al. (2) to present a detailed description of the epi-cardial projections of the cardiomotor nerves to all surfaces of the left ventricle. Methods Fourteen healthy mongrel dogs weighing 10 to 16 kg were given phencyclidine (Semylan), 2 mg/kg intramuscularly, and then anesthetized with alpha chloralose, 60 to 80 mg/kg given intravenously. We opened the thorax through both fifth intercostal spaces and transected the sternum. Respiration was maintained with a Harvard pump through a tracheotomy tube. We isolated the left and right stellate ganglia and, following an anterior longitudinal pericardiotomy,