Changes in heart rate variability in elderly patients undergoing major noncardiac surgery under spinal or general anesthesia

Time-course of heart rate variability after total hip arthroplasty

Heart rate variability (HRV) is a measure of the autonomic nervous system function and possibly related to postoperative outcome. Despite several HRV studies in different surgical settings, optimal indices and timepoints for measuring have not been adequately determined. Consequently, there is a need for detailed descriptive procedure-specific studies on the time-course of perioperative HRV within a modern fast-track surgical setting. We measured HRV continuously in 24 patients from 4 days before until 9 days after total hip arthroplasty (THA). Statistical methods included mainly ANOVA and t-tests or Kruskal-Wallis and pairwise Wilcoxon test. Patients completed the Orthostatic Discriminant and Severity Scale five times during the study describing autonomic nervous system dysfunction. Standard deviation between normal-to-normal beats and the total power of HRV were reduced for at least 9 days following THA, with a trend towards increased HRV leading up to the day of surgery. The balance between low- and high-frequency power of HRV was reduced in the postoperative evenings. There was increased orthostatic intolerance symptoms on the first postoperative day, with symptoms of pain, fatigue and weakness decreasing after the first postoperative day. Median hospital stay was 1 day. We provide the first detailed description of perioperative time-course of HRV and orthostatic symptoms in fast-track THA, showing reduced HRV after surgery for at least a week, and that HRV changes are sensitive to time of day and timing before and after surgery. These results are helpful in designing future HRV studies in perioperative risk assessment and outcome.

Evaluation of remifentanil anesthesia for off-pump coronary artery bypass grafting surgery using heart rate variability

Heart rate variability (HRV) was used in the present study to evaluate a target-controlled approach compared with a constant-rate infusion for remifentanil anesthesia during off-pump coronary artery bypass grafting (OP-CABG) surgery. A total of 65 patients with American Society of Anesthesiologists (ASA) physical status II or III, who were aged 60–85 years and scheduled for OP-CABG, were selected for the study. All patients were administered an intramuscular premedication of 10 mg morphine and 0.3 mg scopolamine. In group I, remifentanil was infused using a target-controlled approach at 1.5–5.0 ng/ml, and in group II, remifentanil was infused at a constant-rate of 0.05–1.0 μg/kg/min and at additional single increments of 1 μg/kg when appropriate. The heart rate and other hemodynamic monitoring indices of the patients, including the mean arterial pressure, central venous pressure, pulmonary artery pressure and pulmonary capillary wedge pressure, were monitored at various time points, including prior to induction (T₀), at extubation (performed intraoperatively; T₇) and at 24 h post-surgery. The HRV indices, including total power (TP), low frequency (LF) and the LF/high frequency (HF) ratio of power (LF/HF), were reduced following induction at T₀ and remained low at 24 h post-surgery. At T₅ (right coronary or left circumflex artery anastomosis) and T₇ (tracheal extubation), all the HRV indices, with the exception of the HF power, were significantly increased (P<0.05). Additionally, the TP, LF and LF/HF values in group II were higher at T₅ compared with those in group I (P<0.05). Remifentanil target-controlled infusion is superior to constant-rate infusion in suppressing the stress response during OP-CABG, maintaining the balance of the cardiac autonomic nervous system and promoting the recovery of the autonomic function following surgery.

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.