Right vagal nerve stimulation during minimally invasive direct coronary artery bypass grafting in dogs : a preliminary study

Abstract

Minimal access coronary artery bypass grafting without cardiopulmonary bypass has been used with increasing frequency. However, some surgeons are still unwilling to perform MIDCAB because the anastomosis is technically demanding. The aim of this study was to assess whether autonomic activation via right vagal nerve stimulation will be an effective support technique on heart rate during MIDCAB in dogs. Preliminary study. Cardiothoracic Surgery Unit, University Clinic. The right cervical vagal nerve was stimulated in five dogs. In one dog, right thoracotomy was performed to isolate the vagal nerve. Bipolar hook electrodes were attached to the vagal nerve. The vagal nerve was stimulated (3-5 mA, 40 Hz) for a few seconds while suturing the coronary artery. Experiments were conducted in two groups. In Group I, two dogs received vagal stimulation via the right neck, and one dog received vagal stimulation via the right thoracic cavity approach. In Group H, all vagal stimulations were performed via the neck during intravenous infusion of diltiazem (10 mg/hrs) or verapamil (5 mg/hrs). In Group I, when the cervical nerve stimulation started the heart rate decreased from 190 to 45 beats/min in one dog, and from 180 to 42 beats/min in another dog. During thoracic nerve stimulation, the heart rate decreased from 205 to 70 beats/min. In Group II, vagal stimulation of one dog (10 mg/hr diltiazem) caused ventricular arrest, and in the other dogs (5 mg/hr verapamil) vagal stimulation caused marked bradycardia with atrioventricular block. After the cessation of nerve stimulation, the heart rate returned to normal sinus rhythm immediately in each dog. Based on our findings, this type of autonomic stimulation (especially with i.v. administration of diltiazem or verapamil) can be an effective technique in reducing heart beats, thus obtaining relatively quiet surgical field for coronary anastomosis in CABG without cardiopulmonary bypass.