Cardiac surgery starting in the late morning is linked to a modest increase in cardiovascular mortality compared with other times of day, according to a study led by researchers at the University of Manchester.

The secondary analysis, published in the journal Anaesthesia, sought to investigate the link between the timing of cardiac surgery and mortality outcomes. A total of 24,068 adults undergoing planned elective or urgent cardiac surgery between 2009 and 2016 across four linked datasets were included.

Patients undergoing emergency or salvage surgery, or procedures commencing overnight, were excluded.

Operations were categorised as early morning (07:00–09:59), late morning (10:00–11:59), early afternoon (12:00–13:59), or late afternoon (14:00–19:59). Early morning procedures accounted for 47% of surgeries.

The primary outcomes were cardiovascular death and hospital readmission with myocardial infarction or acute heart failure within 180 days of surgery. Secondary outcomes included postoperative length of stay, major adverse cardiovascular events (MACE) and all-cause mortality.

Mortality risk and late morning cardiac surgery

Patients undergoing late-morning surgery had the highest predicted operative mortality risk, with a mean European System for Cardiac Operative Risk Evaluation 2-predicted mortality of 3.7%, compared with 3.2% for early-morning surgery, 2.8% for early-afternoon surgery and 3.1% for late-afternoon procedures.

After adjustment for operative risk and cross-clamp time, late-morning surgery was associated with an 18% higher hazard of cardiovascular death compared with early-morning procedures (adjusted hazard ratio [HR] 1.18; 95% CI 1.00–1.39).

However, no significant differences were observed for hospital readmission with myocardial infarction or acute heart failure (adjusted HR 0.97; 95% CI 0.85–1.11).

No differences were identified across operative timing groups for secondary outcomes, including all-cause mortality, MACE or postoperative hospital stay. Adjusted HRs for all-cause mortality and MACE were 1.08 (95% CI 0.96–1.22) and 1.03 (95% CI 0.93–1.14), respectively.

The researchers added that the early divergence observed in Kaplan–Meier curves suggested that any excess mortality was more likely attributable to perioperative factors rather than long-term disease progression.

Circadian biology and mortality outcomes

The authors discussed several potential mechanisms influencing the timing of cardiac surgery on outcomes, including circadian variation in inflammatory responses and myocardial tolerance to ischaemia–reperfusion injury mediated through the intrinsic cardiac clock.

They noted that previous experimental and translational research has implicated circadian clock genes in perioperative myocardial injury.

Several limitations were acknowledged, including the retrospective observational design, inability to establish causality, potential residual confounding and the need for data imputation.

Possible bias introduced during data linkage, the lack of adjustment for seasonal variation and inter-centre differences in surgical practice, and limited generalisability beyond the UK healthcare system were noted as additional limitations.

Although the dataset predated the Covid-19 pandemic, the authors argued that it still reflected clinically relevant contemporary cardiac surgical populations.

Lead author Dr Gareth Kitchen, clinical senior lecturer at the University of Manchester, said: ‘Given that over 25,000 heart operations are performed across the UK every year with around a 2.7% mortality, even small improvements in timing-related outcomes could have significant benefits to patients.

‘This research shows a slightly higher risk of heart-related mortality is likely to occur when heart surgery starts in late morning.

‘However, though the risk is statistically significant, it is relatively modest and patients can be reassured that most people will almost certainly be unaffected.’

Dr Kitchen added that it is ‘our duty as clinicians to ensure the best possible outcomes, and moderating timings is a potentially inexpensive method to achieve that’.

The authors concluded that future research should explore whether integrating circadian biology into perioperative planning could support more personalised surgical scheduling based on individual chronotypes.

They also added that prospective trials and large-scale analyses incorporating wearable circadian data and electronic health records may help determine whether precision timing of cardiac surgery can optimise patient outcomes.

Reference
Kitchen G et al. Time of day of cardiac surgery and postoperative outcomes in the UK: a secondary analysis of linked national datasets. Anaesthesia 2026;81:775–82.