Selective vagal innervation of sinoatrial and atrioventricular nodes in canine heart

Abstract

Parasympathetic pathways mediating chronotropic and dromotropic responses to cervical vagal stimulation were determined from sequential, restricted, intrapericardial dissection around major cardiac vessels. Although right cervical vagal input evoked significantly greater bradycardia, supramaximal electrical stimulation of either vagus produced similar ventricular rates, both with and without simultaneous atrial pacing. Dissection of the triangular fat pad at the junction of the inferior vena cava-inferior left atrium (IVC-ILA) invariably eliminated all vagal input to the atrioventricular (AV) nodal region. Yet IVC-ILA dissection had minimal influence on evoked-chronotropic responses to either cervical vagal or stellate ganglia stimulation. Respective intrapericardial projection pathways, from either right or left vagi, are sufficiently distinct to allow unilateral parasympathetic denervation of the sinoatrial (SA) and atrioventricular (AV) nodal regions. Left vagal projections to the SA and AV nodal regions course primarily along and between the right pulmonary artery and left superior pulmonary vein. Right vagal projections to the SA and AV nodal regions are somewhat more diffuse but concentrate around the right pulmonary vein complex and adjacent segments of the right pulmonary artery. We conclude there are parallel, yet functionally distinct, inputs from right and left vagi to the SA and AV nodal regions.