Patterns of Sympathetic Nerve Projections onto the Canine Heart

Major branches from right and left sympathetic ganglia were electrically stimulated while force of contraction was recorded from multiple areas of the right and left ventricles. Stimulation of the stellate ganglia generally elicited alterations in force of contraction from all test segments, but excitation of selected nerve trunks induced responses in highly localized regions of the heart. Ablation of narrow strips of epicardium resulted in obliteration of contractile responses in specific, highly localized regions of the heart; thus a major fraction of the sympathetic innervation of the ventricular chambers is by way of the epicardial plexus. The anterior surface of the right ventricle is supplied by projection pathways arising within the immediately subepicardial regions of the right A-V groove and, to a lesser extent, from the tissues immediately adjacent to the left anterior descending artery. The left ventricle receives minor projections from the right A-V groove with major projections from subepicardial tissues along the left anterior descending artery. In some animals there also exists a definite left ventricular supply from the region of the left A-V groove. Whereas the thoracic vagi send dense projections to the atria, and particularly to nodal tissue, they also supply both ventricles with inhibitory and augmentor fibers. Although isolated cardiac nerves may carry predominantly sympathetic or parasympathetic fibers, many show rich intermingling of these fibers in trunks distal to the caudal cervical ganglion.