Significance of spinal autonomic loci in post coronary ligation arrhythmia

Abstract

Two-stage coronary artery ligation in dogs consistently induced ventricular ectopics and raised plasma catecholamine and free fatty acid levels. Ether or pentobarbitone anaesthesia completely abolished the cardiac irregularities and lowered the plasma catecholamine and free fatty acid levels. Chloralose anaesthesia, on the other hand, did not affect the ventricular ectopics, plasma catecholamines and free fatty acids. Haemorrhagic hypotension did not alter the incidence of ventricular ectopics following coronary artery ligation. In chloralose anaesthetized dogs, the neural factors concerned in the genesis of cardiac arrhythmias following coronary artery ligation were analysed by surgical and pharmacological procedures. Bilateral vagotomy, mid-collicular or spinal (C1) transection did not significantly influence the incidence of ventricular ectopics. Spinal (C4-T6) cord destruction completely abolished ventricular ectopics, restored normal rhythm and lowered plasma catecholamine and free fatty acid levels. Spinal anacsthesia with xylocaine was also found to completely abolish ventricular ectopics. Cardiac sympathectomy or bilateral adrenalectomy significantly inhibited the ventricular ectopics and lowered plasma catecholamines and free fatty acids. Ganglionic blockade, adrenergic neurone blockade or β-adrenoceptor blockade restored normal sinus rhythm. The results implicate the prime importance of spinal autonomic loci in the integration of reflex cardiac arrhythmia arising from myocardial ischaemia. The afferent and efferent pathways of the reflex seem to be in the sympathetics.