Surgery for Wolff-Parkinson-White syndrome interrupts efferent vagal innervation to the left ventricle and to the atrioventricular node in the canine heart

The hypothesis that cardiac surgery to interrupt accessory pathways also interrupts autonomic nerves to the canine ventricle and to the atrioventricular node was tested in four groups of dogs. Group 1 (n=6) underwent dissection of the atrioventricular fat tissue and cryolesion created by application of a cryoprobe at -60°C for 2 min along the lateral left atrioventricular groove, the same surgical procedure as carried out in patients with Wolff-Parkinson-White syndrome with accessory pathways located in the left ventricular free wall. Group 2 (n=6) underwent dissection of the atrioventricular fat pad alone and group 3 (n=6) dissection and cryolesion along the posterior left atrioventricular groove as performed in patients with Wolff-Parkinson-White syndrome with accessory pathways located in the posterior paraseptal area. Group 4 consisted of 11 non-operated control dogs. Four to 13 days after surgery the ventricular effective refractory period (ERP) was determined during bilateral ansae subclaviae stimulation (4 ms pulses, 2-3 Hz, and 2-3 mA), noradrenaline infusion (0.5 μg·kg−1·min−1), and bilateral vagal stimulation (4 ms pulses, 20 Hz, and current strength to induce asystole or complete atrioventricular block). Atrioventricular nodal conduction (AH interval) and spontaneous sinus cycle length were also determined in group 3 dogs. Ansae subclaviae stimulation and noradrenaline infusion shortened effective refractory period significantly at each left ventricular test site. The amount of effective refractory period shortening induced by ansae subclaviae stimulation did not differ among the test sites except for the posterior left ventricle in group 1 dogs. Responses of effective refractory period to infused noradrenaline were not different among the test sites. Vagally induced effective refractory period lengthening during constant noradrenaline infusion was eliminated in the left lateral and posterior ventricle in group 1 and 2 dogs and in the left posterior ventricle and posterior paraseptal region in group 3 dogs. Choline acetyltransferase activity was significantly reduced in the lateral left ventricle of group 1 dogs. In four of six group 3 dogs vagal effects on the atrioventricular node but not on the sinus node were also interrupted. Sympathetic effects on the atrioventricular node were not interrupted in any dogs. It is concluded that, when applied to a canine model, the extracardiac surgical approach to interrupt accessory pathways also interrupts efferent vagal fibres innervating the left ventricle and atrioventricular node but not efferent sympathetic fibres.