Abstract 16545: Sinus Rhythm Dynamics and Ventricular Ectopy in an Experimental Model of Aging

Abstract

Aging is coupled with alterations of heart rate and heart rate variability (HRV), together with increased incidence of arrhythmias and sudden cardiac death. But whether changes of sinus rhythm properties of the aged heart correlate with enhanced occurrence of ventricular ectopic discharge remains unclear. Thus, we studied the effects of aging on heart rate, HRV, and occurrence of premature ventricular complexes (PVCs) in aging C57Bl/6 mice. Electrocardiograms (ECG) were obtained in male and female conscious mice at ~4, ~12, ~18, and ~24 months of age (n=37-66). Heart rate was preserved at ~4, ~12, and ~18 months (729±30, 730±22, and 725±20 bpm) and reached a minimum at ~24 months (708±37 bpm). Standard deviation of RR intervals, an indicator of HRV, was maximal at ~4 months (3.5±1.7 ms) and was reduced at ~12, ~18, and ~24 months (2.6±1.5, 2.5±1.3, and 2.6±1.3 ms). By frequency domain analysis, high-frequency components of RR interval variations, indicative of parasympathetic influence, were preserved with aging. In contrast, low frequency components, comprising the influence of sympathetic and parasympathetic axis, were maximal in young animals and progressively decrease at ~12, ~18, and ~24 months. PVCs were observed in only 3% of mice at ~4 months, a fraction that increased to 11%, 10%, and 22% at ~12, ~18, and ~24 months, respectively. For each age interval, heart rate and HRV parameters for animals with PVCs were distributed within the range observed in mice not experiencing ventricular ectopy. Moreover, for animals with PVCs, parameters of HRV before the occurrence of ectopic beats were comparable to those observed during undisturbed sinus rhythm, although a tendency for lower heart rate was seen. To address the role of the autonomic nervous system on incidence of ectopic events, ECGs were collected before and after block of the sympathetic and parasympathetic axis in mice at ~4 months (n=30) and ~24 months (n=26). This intervention reduced heart rate in both groups of animals and attenuated HRV exclusively in young. Moreover, combine autonomic block decreased incidence of PVCs by 50% and 57% in young and old animals, respectively. Collectively, these results suggest that occurrence of ventricular ectopy does not correlate with heart rhythm dynamics.