Selective vagal innervation of the heart

Parasympathetic ganglia are imbedded (1) in the epicardial fat pad located on the posterior surface of the dog's heart and (2) immediately overlying the point of penetration by the coronary sinus into the interatrial septum. The fat pad is situated between the inferior vena cava and the inferior left atrium. It contains multiple encapsulated ganglia, each consisting of two to 80 separate cells, richly intermingled with neural elements. Destruction of these ganglia by surgical excision and/or phenol painting interrupts both right and left vagal inhibition of atrio-ventricular (A-V) conduction, without obviously altering vagal modulation of sinoatrial function. Excision or phenol destruction of the fat pad overlying the right pulmonary vein inlets to the left atrium interrupts both right and left vagal inhibition of sinoatrial function, again without interfering with vagal control of atrioventricular nodal function. Well organized, encapsulated autonomic ganglia are also found throughout this fat pad. These experiments thus identify and localize separate concentrations of ganglion cells which differentially modulate automaticity and A-V conduction in the canine heart.