Perioperative myocardial ischemia is associated with a prolonged cardiac vagal dysfunction after non-cardiac surgery

Disturbances in Melatonin, Cortisol and Core Body Temperature Rhythms after Major Surgery

BACKGROUND

It has been suggested that circadian rhythm disturbances are present after major surgery and that this may play a role in the development of postoperative sleep disturbances, fatigue, cognitive dysfunction and cardiovascular morbidity. The objective of this study was to examine the profile of melatonin, cortisol and core body temperature rhythms before and after major surgery.

METHODS

Blood samples (melatonin and cortisol) and core body temperature readings were collected every hour in the 24-h period prior to surgery and the 48 h after surgery from 11 patients undergoing major abdominal surgery. All patients had private rooms. Light exposure was controlled and monitored. Phase markers [50% dim light melatonin onset (DLMO 50%) and offset (DLMOff 50%), cortisol and core body temperature acrophase] for the three circadian rhythm profiles were calculated before and after surgery. The correlation between the melatonin rhythm and time of surgery, duration of surgery and opioid use was examined.

RESULTS

A median delay in the onset of melatonin was seen on the first postoperative day [median DLMO 50% 22:46 hours (range: 21:15-01:08 hours) on the preoperative day compared with 23:54 hours (range: 19:09-02:46 hours) on the first postoperative day; P </= 0.05] . A significant positive correlation existed between the duration of surgery and the time of melatonin onset (r = 0.67, P </= 0.05) . There was a significantly reduced basal secretion of melatonin immediately after surgery, with a subsequent significant increase in maximum melatonin values on the second postoperative night. A median delay of up to 4 h was seen in the timing of the peak of the temperature rhythm on the second postoperative day. Both cortisol secretion and core body temperature were increased after surgery and did not return to preoperative values in the 48 h of the postoperative study period. No significant correlation between opioid dose and the basal or maximum melatonin levels or the time of melatonin onset was found.

CONCLUSION

We found disturbances in three circadian markers after major surgery. The clinical consequences of postoperative circadian disturbances should be investigated further in the future.

Spontaneous baroreflex sensitivity after coronary artery bypass graft surgery as a function of gender and age

The effects of coronary artery bypass graft (CABG) surgery on spontaneous baroreflex (SBR) sensitivity and heart rate variability were examined in 11 women and 23 men preoperatively and 5 days postoperatively. Electrocardiograph R–R interval and beat-by-beat arterial blood pressure data were collected continuously for 20 min in the supine and standing postures. Coarse graining spectral analysis was performed on the heart rate variability data. Spontaneous baroreflex sensitivity declined after surgery with a differential influence of gender. Men showed a decrease in SBR slope following surgery, with a greater decrease in the standing posture; the parasympathetic (PNS) indicator was lower postoperatively and in the standing posture; the reduction in low-frequency (LF) power was greater for the younger men. In women, the PNS indicator was lower in the standing posture. Both men and women showed a decrease in high-frequency power following CABG surgery, which decreased the sensitivity of the short-term cardiac control mechanisms that modulate heart rate, with the greater effects occurring in men. The reduction in SBR sensitivity indicates that the ability of the cardiovascular system to respond rapidly to changing stimuli was compromised. The decline in the PNS indicator implies that patients were vulnerable to the risks of myocardial ischemia, sympathetically mediated cardiac dysrhythmias, and sudden cardiac death.Key words: spectral analysis, spontaneous baroreflex sensitivity, CABG surgery, gender, age, posture.

[Spectral analysis of the ECG R-R interval permits early detection of vagal responses to neurosurgical stimuli]

OBJECTIVE

To assess the efficacy of ECG spectral analysis, compared with heart rate (HR) monitoring in the detection of vagal response to surgical stimuli.

METHODS

Twenty Asa II-III patients (age: 65 +/- 13 years) scheduled for surgery of cerebellopontine angle or implantation of sacral root stimulator were examined. Target controlled infusion of propofol (2-4 microg x ml(-1)) and remifentanil (4 ng x ml(-1)) was guided by the bispectral index (Bis). Arterial pressure via a radial catheter, pulse oximetry and end tidal CO2 were continuously monitored. Spectral analysis was achieved by connecting a computer to the cardiorespiratory monitor. Online power spectrum densities were calculated from the ECG R-R interval by software based on the fast Fourier transform (LabView, National Instruments, USA). Low frequency (LF: 0.04-0.15Hz) and high frequency (HF: 0.15-0.4Hz) were associated with sympathetic and parasympathetic activities respectively. We defined vagal reaction as a decrease in FC or an increase in HF >10% of the prestimuli value. HF and FC were compared according to the detection delay (by a Student t test with p < 0.05 considered significant) and a concordance test with a kappa coefficient (kappa): -1 = total discordance to 1 = total concordance.

RESULTS

Twelve vagal reactions (observed in 8 patients) were detected within 5.5 +/- 1.3 s (HF) and 12.4 +/- 1.6 (FC); p < 0.001. Concordance between the 2 parameters was 95% (kappa =0.9).

CONCLUSION

The ECG spectral analysis is a non-invasive technique, which permits the detection of intra-operative vagal reactions earlier than conventional monitoring of HR.

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.

The use of spectral measures of heart rate variability to differentiate between male snorers and patients with sleep apnoea syndrome

Snoring is a characteristic feature of habitual snorers and patients with sleep apnoea syndrome. However, unlike snorers, sleep apnoea patients have an increased peri-operative morbidity. Presently available methods to differentiate between these two groups are either expensive, invasive or time consuming. As cardiac reflexes are impaired in sleep apnoea syndrome, we tested whether heart rate variability could discriminate between snorers and patients with sleep apnoea syndrome. Heart rate variability measurement detects cardiac autonomic dysfunction non-invasively in an ambulatory setting. We studied 32 male patients undergoing polysomnography for suspected sleep apnoea. Total, low- and high-frequency power were measured using a Holter electrocardiogram. Differences in night- and daytime variability were then calculated. Differences between day and night values were more pronounced in the sleep apnoea group and related to the apnoea-hypopnoea-index and low oxygen saturation. Higher values in sleep apnoea patients resulted from increasing variability at night. Heart rate variability might thus help to differentiate between snorers and patients with severe sleep apnoea syndrome.

Gaining control: can we reduce perioperative cardiovascular complications?

Cardiovascular complications are common in patients at risk for coronary disease undergoing surgery. The role of hyperactivity of the sympathetic nervous system and impaired parasympathetic control mechanisms in the genesis and consequences of perioperative myocardial ischemia has been discussed. Sympathetic blocking drugs of the beta blocker and alpha₂ agonist classes have been used extensively in the perioperative setting to control hemodynamic responses and reduce episodes of myocardial ischemia. To date, perioperative beta blockade is the only strategy shown to improve long-term outcome after surgery in this population.