DIFFERENTIAL EFFECT OF PHARMACOLOGICAL AUTONOMIC BLOCKADE ON SOME ELECTROPHYSIOLOGICAL PROPERTIES OF THE HUMAN VENTRICLE AND ATRIUM

Objective-This study investigated the dominance of each limb of the au tonomic nervous system and tested sympathetic-vagal interactions in th e human ventricle and atrium after administration of propranolol and a tropine. Patients and methods-The 90% monophasic action potential dura tion (MAPD90) and the effective refractory period (ERP) at the right v entricular apex (RV) and the right lateral atrium (RA) were measured i n 14 patients. The MAPD90 was measured during constant RV and RA pacin g (cycle length 600 ms) and the ERP was measured at a driven cycle len gth of 600 ms. Electrophysiological variables were measured during a c ontrol period, after propranolol (0.15 mg/kg loading dose followed by 0.1 mg/min infusion), and after autonomic blockade (atropine 0.04 mg/k g). Results-Both RV MAPD90 and RV ERP increased after propranolol (RV MAPD90 from 268 (26) ms to 275 (26) ms, p < 0.005; RV ERP from 252 (25 ) ms to 258 (26) ms, p < 0.0005) and then decreased to below the contr ol values after autonomic blockade (RV MAPD90 256 (24)ms; RV ERP 239 ( 25) ms, p < 0.0005 v propranolol, p < 0.0005 v control). In contrast, both RA MAPD90 and RA ERP increased after propranolol (RA MAPD90 from 242 (19) ms to 260 (19) ms; RA ERP from 216 (21) ms to 230 (18) ms, p < 0.0005), and then increased slightly more after autonomic blockade ( RA MAPD90 265 (16) ms, p = 0.09; RA ERP 235 (16) ms, p = 0.07), thus r emaining above control values (p < 0.0005). Conclusions-The results in dicate (a) that in the human ventricle vagal stimulation and sympathet ic beta stimulation are antagonistic and that direct vagal stimulation predominates over beta stimulation, with sympathetic-vagal interactio n being minimal and (b) that in the human atrium vagal stimulation and beta stimulation are synergistic and beta stimulation predominates ov er vagal stimulation, with direct vagal stimulation having a minimal e ffect.