Experimental coronary artery ligation in conscious dogs six months after bilateral cardiac sympathectomy

Abstract

The effects of left circumflex coronary artery (LCA) occlusion six months after bilateral cardiac sympathectomy on mortality, arrhythmias, and myocardial norepinephrine were studied with functional and histologic assessment of sympathetic regeneration. Bilateral stellate ganglionectomy, thoracic sympathectomy, and ansectomy (BSTG) were performed on 23 dogs and denervation was confirmed by electrical stimulation. Six months later, the LCA was ligated by a two-stage technique in these dogs (BSTG-6 mo.) and 23 control dogs in the conscious state. All dogs were autopsied at death or after 48 hours. Mortality at 15 minutes from ventricular fibrillation (VF) was 22 per cent in BSTG-6 mo. dogs and 52 per cent in control animals (p < 0.05). Mortality in the two groups at 24 hours was 44 per cent and 65 per cent, respectively. Before LCA occlusion, sinus arrhythmia was present in 23 per cent of the BSTG-6 mo. dogs and 82 per cent of the control animals. A significantly greater percentage increase in the sinus cardiac rate one minute after LCA occlusion was present in control dogs compared to BSTG-6 mo. dogs (p < 0.005). There was a later onset of ventricular arrhythmias, lesser incidence of ventricular premature beats (VPB) and ventricular tachycardia (VT), and a shorter duration of VT in BSTG-6 mo. dogs than in control animals. Myocardial norepinephrine levels were similar in BSTG-6 mo. and control dogs and fell after coronary occlusion by a comparable degree in the healthy and infarcted ventricles in both groups. Upper thoracic spinal cord stimulation (SCS) produced a mean 10 per cent increase in heart rate of three dogs four weeks after BSTG; and a 21 per cent increase in five BSTG-6 mo. animals in contrast with a 78 per cent increase in five control animals. Only one BSTG-6 mo. dog showed an almost normal (68 per cent) response to SCS. Histologic studies showed neural regeneration on the right side in one out of four BSTG-6 mo. dogs. Thus after six months, BSTG still confered a protective effect from VF following experimental coronary occlusion in conscious dogs, especially in the early, most critical period following myocardial infarction. Functional and histologic studies demonstrated sympathetic re-innervation in 20 to 25 per cent of the BSTG-6 mo. dogs.