INCIDENCE OF ARRHYTHMIAS AND HEART-RATE-VARIABILITY IN WILD-TYPE RATSEXPOSED TO SOCIAL STRESS

Psychological stressors of different natures can induce different shie s of autonomic control on cardiac electrical activity, with either a s ympathetic or a parasympathetic prevalence. Arrhythmia occurrence, R-R interval variability, and plasma catecholamine elevations were measur ed in male wild-type rats exposed to either a social stressor (defeat) or a nonsocial challenge (restraint). Electrocardiograms were telemet rically recorded, and blood samples were withdrawn through jugular vei n catheters from normal, freely moving animals. Defeat produced a much higher incidence of arrhythmias (mostly ventricular premature beats), which were mainly observed in the 60-s time periods after attacks. Th e social challenge also induced a much stronger reduction of average R -R interval, a lower R-R interval variability (as estimated by the tim e-domain parameters standard deviation of mean R-R interval duration, coefficient of variance, and root mean square of successive difference s in R-R interval duration), and higher elevations of venous plasma ca techolamines compared with restraint. These autonomic and/or neuroendo crine data indicate that a social stressor such as defeat is character ized by both a higher sympathetic activation and a lower parasympathet ic antagonism compared with a nonsocial restraint challenge, which res ults in a higher risk for ventricular arrhythmias.