Autonomic mechanisms in heart rate variability after isoproterenol-induced myocardial damage in rats

The effect of isoproterenol-induced myocardial damage on heart rate variability was examined in conscious, unrestrained, male, Sprague-Dawley rats. We used power spectrum analysis of beat-to-beat heart rate to study the levels and interaction of sympathetic and parasympathetic neural influences on the heart. One day after isoproterenol (80 mg/kg s.c.), mean heart rate was significantly elevated when compared to controls (isoproterenol 413.9 b.p.m. +/- 7.7 S.E.M.; saline 368.8 b.p.m. +/- 12.8 S.E.M.; P less than 0.05), even though the low frequency and respiratory components of the power spectrum were not different between the two groups. By contrast, a week after isoproterenol administration, heart rate was normal; however, variability in low frequency and respiratory areas of the power spectrum was significantly increased suggesting an abnormal sympathovagal balance. An imbalance in autonomic regulation of cardiac automaticity could account for the 27% incidence of arrhythmias in rats given isoproterenol. These results indicate that autonomic responses associated with isoproterenol-induced myocardial ischemia differ from those in human and in animal models of myocardial infarction.