Cardiac electrical activity during social stress in rats with left ventricular hypertrophy: relations to myocardial structure

Electrocardiographic and behavioral responses to acute social stress (SS), observed in male rats before and one-month after induction of left ventricular hypertrophy (LVH), were correlated with morphometric measurements of the hypertrophied heart. Stress ECGs were recorded from freely moving animals by means of chronically-implanted miniature telemetry transmitters. Strong neuro-en-docrine stimulation of the heart was induced in male individuals by exposing them to lactating female aggression. Normal and LVH rats showed a marked decrease of average R-R interval during SS as compared to baseline conditions and to control animals exposed to simple environmental novelty. Cardiac electrical abnormalities of various nature were observed, ranging from ventricular arrhythmias of different complexity to episodes of II degree A-V block. Among LVH males, a subgroup of animals (subgroup A) showed a markedly higher value of cumulated time of ventricular arrhythmias during stress as compared to the remaining LVH subjects (subgroup B) and to normal animals. Subgroup A rats were also characterized by significantly lower values of R-R interval variability (expressed as variance) and a higher complexity and severity of arrhythmic events. In all LVH animals, the amount of myocardial damage was significantly correlated with cumulated time of arrhythmias: larger areas of interstitial fibrosis were observed in subgroup A, mostly located at the mid and endocardial level of the left ventricular wall. The data suggest a close relationship among sympathetic activation, incidence of ventricular arrhythmias and amount of myocardialdamage of the hypertrophied rat heart.