Epicardial phenol interrupts refractory period responses to sympathetic but not vagal stimulation in canine left ventricular epicardium and endocardium.

Abstract

The effects of regional epicardial application of phenol were studied on autonomic neural control of electrophysiological characteristics of the anterior left ventricle. In 8 open-chest dogs, a thin line of 88% phenol was applied on the perimeter encircling a multipolar electrode; the effective refractory period (ERP) was measured. Electrograms in phenol-encircled and untreated areas were recorded. Before phenol was applied, sympathetic nerve stimulation shortened ERP in all areas: percent change (.delta.) .gtoreq. 12. Phenol application to an area with a radius of 1-2 cm prevented ERP shortening in encircled epicardium during sympathetic stimulation, %.delta. = 0.9 .+-. 0.8 (standard error of the mean) and attenuated ERP shortening in underlying endocardium %.delta. = 2.5 .+-. 1.6, compared to ERP shortening in untreated areas, %.delta. = 10 .+-. 1. A subsequent phenol application to an area with a radius of 2-3 cm prevented ERP shortening during sympathetic stimulation in encircled epicardium and underlying endocardium. Phenol did not alter electrograms, activation times or ERP shortening produced b norepinephrine infusion; electrophysiological characteristics of ventricular muscle encircled by phenol evidently were unchanged apart from effects of withdrawal of sympathetic neural influence. Norepinephrine content measured in phenol-treated epicardium and endocardium of 3 dogs was 7 and 21%, respectively, of the norepinephrine content of untreated areas. In 8 additional dogs, vagus nerve stimulation during norepinephrine infusion prolonged ERP by 3-5 m before and after phenol encircling an area with a radius of 2-3 cm. In these dogs phenol did prevent ERP shortening during sympathetic nerve stimulation. Epicardial phenol apparently interrupts sympathetic neural influences to epicardial and endocardial sites without impairing responses either to i.v. norepinephrine or to vagus nerve stimulation.