Abstract P1097: Heart Rate Variability Analysis In Rodents Reveals Altered Cardiac Autonomic Regulation Following Myocardial Infarction

Heart rate variability (HRV) is an index of cardiovascular health and reflects the ability of the heart to modify beating rate in response to neurohumoral factors. Alterations of HRV have been reported in patients with myocardial infarction (MI), but whether experimental models of ischemic disease recapitulate features of HRV observed in human remains to be clarified. HRV was evaluated in female mice using electrocardiograms collected in the conscious, restrained state using a tunnel device. Naïve mice and animals after permanent coronary artery ligation (MI) were studied. HRV was assessed using time-domain, frequency-domain, and non-linear parameters. By echocardiography, all infarcted animals presented akinetic anterior LV free wall and, respect to naïve mice, a 1.8-fold increase in LV diameter and a 64% reduction in ejection fraction. At 3 to ~30 days after MI, RR interval duration was preserved with respect to non-infarcted mice, whereas standard deviation of RR interval duration (SDRR), was reduced by 61-70% at 3 days to ~30 days after MI. Standard deviation of instantaneous (SD1) and long-term (SD2) RR interval variability, indicative of parasympathetic and sympathetic influence, respectively, were derived from Poincaré plots of RR i and RR i+1 intervals. SD1 and SD2 were reduced after MI (64-73% and 61-70%, respectively). Moreover, by frequency-domain analysis, the contribution of high- (1.5-5 Hz), low- (0.15-1.5 Hz), and very low-frequency (0-0.15 Hz) components of RR interval oscillations were assessed. High-frequency components, which are under the influence of the sympathetic nervous system, were not affected after MI; low-frequency oscillations, attributed to baroreflex-mediated modulation of heart rate, were reduced at 3 and 7 days after MI, whereas very low-frequency components, attributed to the modulatory action of the renin-angiotensin system, thermoregulation, and, partly, parasympathetic activity, were reduced from 3-30 days after MI. Moreover, the ratio between low and high frequency components, indicative of sympathovagal balance, was reduced after MI. In conclusion, myocardial infarction in rodent results in altered heart rate variability, which appears to be secondary, in part, to altered autonomic regulation.