Abstract 2486: Circadian Short-term Heart Rate Variability Deteriorates in Beta Knock Out Mice
Introduction: The aim of the present study was to evaluate changes in heart rate (HR) and HR variability (HRV) with respect to the circadian rhythm in beta-adrenoceptor 1, 2, and 3 knock out (KO) versus wild type mice (WT).
Methods: A 24-hour-ECG was performed in 19 WT at the age of 5 months and in 9 KO at the age of 7 months. After implanting a telemetric transmitter in a subcutaneous cavity in the neck of the mice the ECG recording was started on the third postoperative day. The sampling rate was 400 Hz. Individual channels were amplified and filtered between 10 and 100 Hz. HR as well as HRV was analyzed off line (AD Instruments, Milford, MA, USA). HRV was calculated with time and frequency domain analysis. To demonstrate changes in circadian pattern the 24 hour ECG was analyzed 3 times a day: at 2 a.m., 7 a.m., and 5 p.m..
Results: The table⇓ demonstrates the results. (†:p<0.01 for WT versus KO; *: p<0.05 for WT versus KO for each time).
Conclusions: The lack of sympathetic beta-adrenergic myocardial receptors (1,2,3) resulted in a decrease of HR. But, circadian patterns seemed to be uninfluenced. Comparing WT and KO, KO mice showed a decrease of HRV and circadian rhythmic dissolves. The results of short term HRV clearly demonstrated a significant change in the two branches of the autonomic nervous system towards the vagal component. Accordingly, these data show that the loss of sympathetic beta-adrenergic stimulation decreases HRV and is responsible for circadian pattern.