Diminished Circadian Rhythm of Heart Rate Variability After Aortic Surgery Appears to Be Independent of Myocardial Ischemia

Impaired heart rate variability (HRV) has been described postoperatively. Diminished HRV may be related to myocardial ischemia and potentially causes circulatory instability. Cardiac ischemic events and a compromised cardiovascular function are not uncommon after aortic surgery. Circadian variation of HRV seems to be a prognostically more important parameter than HRV itself with respect to the development of cardiac dysfunction. We therefore investigated whether the diurnal rhythm of HRV is simultaneously altered postoperatively and the potential contribution of myocardial ischemia. After approval by the hospital ethics committee and having obtained informed consent, we studied 11 consecutive male patients undergoing elective aortic surgery. Patients were monitored with a Holter-ECG perioperatively. Spectral HRV measures (total, low, and high frequency power) were determined and night/day ratios calculated. Ischemic ECG changes were recorded and serum was sampled for troponin T analysis. A remarkable decline in circadian variation accompanied the decrease in all HRV parameters postoperatively. Five patients showed ECG changes suggestive of myocardial ischemia and two had increased levels of troponin T. These two patients showed greatly diminished HRV postoperatively with a similarly reduced circadian rhythm. We have demonstrated that the circadian rhythm of HRV is not preserved after aortic surgery. Diminished diurnal variability seems to be a general manifestation and myocardial ischemia may just be one contributing factor. An altered biorhythm in combination with stress related changes in the neuroendocrine system after surgery most likely have a more significant influence on the circadian rhythm of HRV.