Selective vagal postganglionic innervation of the sinoatrial and atrioventricular nodes in the non-human primate

The distribution of parasympathetic postganglionic nerves to the atrioventricular (AVN) and sinoatrial nodal (SAN) regions was investigated in the non-human primate heart. Eight male monkeys ( Macaca fascicularis) weighing 5.5–7.0 kg. were anesthetized (α-chloralose, 50 mg/kg and urethane, 500 mg/kg) and instrumented to measure arterial pressure, electrocardiogram, atrial and ventricular electrograms. The cervical vagi were electrically stimulated (20 Hz, 4 V, 2 ms) before and after selective denervation (D) of the AVN and/or SAN. Vagal stimulation was repeated during atrial pacing to assess parasympathetic modulation of AVN conduction. Ablation of parasympathetic pathways to the AVN, accomplished by the disruption of the epicardial fat and surface muscle layer at the junction of the inferior vena cava and inferior left atrium eliminated ( P < 0.01) the dromotropic effects of vagal stimulation without affecting the heart rate response (right vagus, before D, paced: atrial rate 218.0 ± 6.3, ventricular rate 67.1 ± 23.7; after D: atrial rate 210.3 ± 6.4, ventricular rate 210.3 ± 6.4 beats/min, x ̄ ± S.D. ). In sharp contrast, surgical dissection of the fat pad overlying the right pulmonary vein-superior vena cava junction significantly ( P > 0.01) attenuated negative chronotropic effects of vagal stimulation (left vagus, before D the R-R interval increased by 832.7 ± 146.4 ms, 209.5% increase; after D 37.4 ± 18.0 ms, 8.8% increase). These data demonstrate discrete vagal efferent pathways innervate both the SAN and AVN regions of the non-human primate heart.