Rationale

Circadian rhythms affect cardiovascular function, and the timing and severity of stroke and myocardial infarction (commonly known as a heart attack). Afternoon cardiac surgery may improve outcomes by reducing ischaemia‐reperfusion injury (i.e. reducing tissue damage caused when blood supply returns to tissue (reperfusion) after a period of oxygen deprivation (ischaemia)). However, the evidence is conflicting. This systematic review assessed the impact of surgical timing on clinical outcomes after cardiac surgery.

Objectives

To assess the effects of early versus late surgical start times for on‐pump cardiac surgery on mortality, cardiac outcomes, and quality of life.

Search methods

We searched CENTRAL, MEDLINE, Embase, and Web of Science Conference Proceedings Citation Index ‐ Science, along with ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform trials registers. We also conducted reference checking, citation searching, and contacted study authors to identify studies for inclusion. The latest search date was 26 January 2025.

Eligibility criteria

We included randomised controlled trials (RCTs) in adults undergoing cardiac surgery comparing late with early surgical start times. We excluded non‐randomised studies and studies in children.

Outcomes

Our critical outcomes were short‐term mortality (≤ 30 days postoperative), long‐term mortality (> 30 days postoperative), and perioperative myocardial infarction. Other important outcomes were perioperative myocardial injury, postoperative atrial fibrillation, left ventricular ejection fraction, lengths of intensive care unit (ICU) and hospital stays, and quality of life.

Risk of bias

We used the Cochrane Risk of Bias 2 tool to assess bias in the included RCTs.

Synthesis methods

As only one study met the inclusion criteria, we did not perform meta‐analysis. We synthesised results descriptively, and used GRADE to assess the certainty of the evidence for specified outcomes.

Included studies

We included one study with 88 participants. The included study was conducted in France, and reported on differences in outcomes between morning and afternoon on‐pump elective aortic valve replacement in adults.

Synthesis of results

Critical outcomes

No study reported short‐term or long‐term mortality data for early versus late surgical start times for on‐pump cardiac surgery. In the included study, there was no evidence of a difference regarding in‐hospital mortality between groups, with no deaths in both groups (risk ratio (RR) and 95% confidence interval (CI) not estimable; 1 study, 88 participants).

The evidence is very uncertain about the effect of early versus late surgery on perioperative myocardial infarction (RR 0.29, 95% CI 0.06 to 1.30; 1 study, 88 participants, very low‐certainty evidence).

Important outcomes

There was evidence of lower perioperative myocardial injury as measured by cumulative troponin release over 72 hours in those undergoing late surgery compared to early surgery (MD −46 ng/L × 72 h, 95% CI −79 to −13; 1 study, 88 participants).

In the included study, there was no evidence of a difference in new‐onset postoperative atrial fibrillation during hospital stay between groups (RR 0.75, 95% CI 0.40 to 1.40; 1 study, 88 participants).

No study reported differences in left ventricular ejection fraction at discharge as a continuous variable for early versus late surgical start times for on‐pump cardiac surgery. In the included study, there was no evidence of a difference in left ventricular ejection fraction < 45% at discharge between groups (RR 0.40, 95% CI 0.08 to 1.95; 1 study, 88 participants).

No study reported differences in length of ICU admission for early versus late surgical start times for on‐pump cardiac surgery. There was no evidence of a difference in need for inotropic support between groups in the included study (RR 0.25, 95% CI 0.03 to 2.15; 1 study, 88 participants).

The evidence is very uncertain about the effect of late surgery on length of hospital stay (MD 0.00, 95% CI −1.48 to 1.48; 1 study, 88 participants, very low‐certainty evidence).

No study reported on the outcome of quality of life.