Heart damage following surgery is more common among people who undergo the surgeon’s knife in the morning, new research in The Lancet reports.

The single centre study from  France  found that patients undergoing aortic valve replacement in the afternoon had a 50% lower risk of a major cardiac event, compared to people who had surgery in the morning.

According to the authors, led by professor David Montaigne from the University of Lille-France, the study’s findings indicated that a clinically relevant biorhythm exists in myocardial ischaemia reperfusion intolerance.

“Through consideration of the timing of surgery, it could be possible to improve outcomes in these patients, with afternoon surgery providing perioperative myocardial protection and better outcomes,” the research team say.

The research consisted of an observational study, a randomised controlled trial,  a human tissue analysis and a mouse model.

In the observational study the research team tracked the medical records of 596 people who had aortic valve replacement surgery (half  in the morning, half in the afternoon) for 500 days.

People who had surgery in the afternoon had a 50% lower risk of a major cardiac event, compared to people who had surgery in the morning (28/298 [9.4%] compared to 54/298  [18.1%]).

This equated to one major event being avoided for every 11 patients who have afternoon surgery.

In the randomised part of the research 88 patients were randomly scheduled for heart valve replacement surgery in the morning or afternoon (50/50) and their health was monitored until they left hospital.

There were no deaths in either group and the average time in hospital was 12 days. However, patients who had afternoon surgery had lower levels of heart tissue damage after surgery, compared to morning surgery patients.

To further explore these differences in outcomes the researchers then tested 30 heart tissue samples from a sub-group of patients from the randomised controlled trial.

Contraction recovery after the hypoxia-reoxygenation challenge was significantly better in the myocardial samples obtained from biopsies taken from patients randomised to afternoon surgery.

A genetic analysis of the samples revealed that 287 genes linked to the circadian clock were more active in the afternoon surgery samples, compared to the morning surgery samples.

“The results of our study show a clinically significant morning versus afternoon variation in myocardial tolerance to the controlled ischaemia-reperfusion insult imposed during cardiac surgery,” they wrote.

“To put our findings into perspective, a few years ago, David J Lefer wrote an editorial asking “whether there is a better time to have a heart attack?”…We show here that the afternoon is probably a better time to undergo cardiac surgery than the morning, and is associated with a better mid-term prognosis,” they concluded.