Selective ganglionic blockade of vagal inputs to sinoatrial and/or atrioventricular regions

Vagal postganglionic neurons to sinoatrial (SAN) and atrioventricular (AVN) nodal regions of the canine heart have been localized surgically around the right pulmonary vein-atrial fat pad and in the fat pad overlying the epicardium at the inferior vena cava-inferior left atrial junction, respectively. Local ganglionic blocking doses (total of 5 mg per injection) of hexamethonium were injected into the pulmonary vein-atrial fat pad to block selectively right and left vagal inputs to the SAN region without interrupting vagal inputs to AVN. Conversely, hexamethonium injected into the inferior vena cava-inferior left atrial pad selectively blocked vagal control of arteriovenous conduction without interfering seriously with vagal control of SAN function. Vagal ganglia situated in pulmonary vein-atrial fat pad also exercise moderate but incomplete control of right atrial contractile force. Lesser vagal control of atrial inotropism is localized in the inferior vena cava-inferior left atrial fat pad. Ganglia situated in a large fat pad on the dorsal epicardial surface of the left atrium (left atrial fat pad) appear to play little or no role in SAN or AVN regulation, although some left preganglionic axons may pass through it en route to the AVN region. Vagal stimulation is associated with prompt and profoundly negative chronotropic and dromotropic responses, but in response to the same stimulation, a negative change in atrial contractile force is much slower in development and is much longer lasting. Such precise anatomical localization and differentiation of the intrinsic vagal regulation of SAN, AVN and contractile force opens new avenues of research on the neural regulation of cardiac performance.