Heart and lungs

Afternoon open heart surgery 'leads to fewer complications', study reports

"Afternoon heart surgery has lower risk of complications, study suggests," says The Guardian.

Researchers in France were interested in whether the time of day of the operation was carried out affected the rate of complications following a type of open heart surgery known as aortic valve replacement. This involves removing the aortic valve (which controls the flow of blood out of the heart) and replacing it with animal or synthetic tissue.

It has been known for some years that our body clock can have a significant effect on critical biological functions – work in this field won the 2017 Noble Prize for Medicine – so researchers wanted to see if the timing of surgery affected surgical outcomes. Their hypothesis was that as the heart has been conditioned to work harder in the afternoon, performing an aortic valve replacement in the afternoon may reduce the risk of complications.

They found the rate of major cardiovascular complications, such as heart attack and heart failure, was halved among people who had the surgery in the afternoon.

However, this study focused on one hospital, with few surgeons and patients, and one specific type of surgery. It could be the case that it was the different surgical teams, rather than the timing of the surgery, that made the difference.

The results need further investigation through larger studies involving multiple sites, as well as different types of heart surgery.

Where did the story come from?

The study was carried out at a single hospital in France by researchers from the University of Lille, the University Hospital CHU Lille, the Institut Pasteur de Lille, and Inserm (U1011 and U1177). It was funded by the Fondation de France, Fédération Française de Cardiologie, Agence Nationale de la Recherche and the CPER-Centre Transdisciplinaire de Recherche sur la Longévité.

It was published in the peer-reviewed medical journal The Lancet.

The UK media headlines reporting this story were very misleading. The Telegraph said: "Surgery is safer in the afternoon," implying that the research had looked at many types of surgery. And BBC News said: "Heart surgery survival chances 'better in the afternoon'," suggesting the research had looked at death rates when, in fact, the study looked at a range of complications. A total of six people died in the study, but there was no significant difference in terms of when they had surgery.

Most of the coverage also talked in general terms about "heart surgery", even though this research only looked at one specific type.

What kind of research was this?

This research involved three different types of investigation. Firstly, the researchers looked at a cohort of consecutive people receiving heart valve surgery in one French hospital, comparing the time of day they had surgery with surgery outcomes.

They then used a randomised controlled trial (RCT) to allocate people to a specific time slot – either morning or afternoon.

Finally, they carried out a laboratory study looking at heart tissue samples from people in the trial to examine various biomarkers associated with heart stress.

These are all valid ways of investigating the question at the core of the research. An RCT is the optimal way to look at the specific effects of an intervention (in this case, the time of operation) as randomising the participants to the different groups should get rid of any differences between them that otherwise influence the results. However, the RCT had only a very small number of operations and surgeons.

What did the research involve?

The cohort study looked at all consecutive patients (596) needing aortic valve replacement at Lille University Hospital between 2009 and 2015. To be included, people had to:

  • be aged 18 or over
  • have severe aortic stenosis (narrowing of the valve where the heart connects with the aorta, the large artery supplying blood to the rest of the body)
  • have "preserved left ventricular ejection fraction" (meaning their heart otherwise functions well and can still pump blood effectively)

The participants could also be having a coronary artery bypass graft (CABG) at the same time as aortic valve replacement, but people with other types of valve disease or congenital heart disease, or those who had previously had heart surgery, were excluded from the study.

The RCT took place from 2016 to 2017 and involved 88 adults meeting the same criteria, except the operations were limited to those having valve replacement without CABG, and the researchers also excluded people who had diabetes, impaired kidney function, and atrial fibrillation or atrial flutter (heart rhythm problems).

Tissue samples were taken from the first 22 people in the trial, to look at biomarkers in the heart muscle cells. The samples were exposed to conditions where the oxygen supply was reduced and then reinstated to see how the cells behaved.

People in the cohort study were followed up for a period of 500 days after their operation, and those in the RCT were observed until they were discharged from hospital. The main outcome of interest in both cases was major cardiovascular events, which included cardiovascular death, heart attack or hospital admission for heart failure.

What were the basic results?

In the cohort study:

  • 4 people who had surgery in the morning (1%) and 2 who had surgery in the afternoon (0.5%) died during their hospital stay. This was not a statistically significant difference.
  • Major adverse cardiac events were less common in the afternoon, occurring in 28 people (9%), compared with 54 people (18%) in the morning group (hazard ratio [HR] 0.50, 95% confidence interval [CI] 0.32 to 0.77).
  • There was no significant difference in rates of cardiovascular death between the groups, but there were fewer cases of acute heart failure in the afternoon group – 14 people (5%) in the morning group and 4 (2%) in the afternoon group (HR 0.36, 95% CI 0.15 to 0.88).

For the smaller group of people involved in the RCT:

  • No patients in either group died during their stay in hospital.
  • Cardiac troponin (a biomarker of heart muscle stress) was higher in the morning group than in the afternoon group.
  • Although there were some between-group differences in various outcomes, such as heart attacks and rhythm problems, these were not statistically significant. This may have been due to the small size of the study.

In the laboratory study:

  • Contraction recovery after the heart muscle was deprived of oxygen and then reoxygenated was better in heart muscle tissue taken from afternoon surgery patients.
  • Further analysis showed the differences may be due to activity of genes involved in the body clock.

How did the researchers interpret the results?

The researchers described the morning-versus-afternoon difference for aortic valve surgery as "clinically significant". They also discussed similar research in other types of heart surgery, such as coronary artery surgery, and noted that the findings were less clear in these other studies.

They suggested that their findings should be investigated further through research based in multiple hospitals rather than at a single site.


This study found evidence of an effect that's worth investigating further to see if there are real differences in heart muscle function and risk of complications from heart surgery at different times of the day. However, there were some limitations:

  • It took place at a single hospital, with a relatively small number of people undergoing operations.
  • The laboratory study found differences in gene activity that suggested the body clock may play a role in making the heart better able to tolerate loss of oxygen and subsequent re-oxygenation. However, there may be other explanations for these differences. For example, all the operations were performed by only 4 different surgeons. Variation in post-operation outcomes could have something to do with the surgeons' performances rather than the patients' characteristics.
  • The research only looked at aortic valve surgery, so we don't know if the same result would be seen for other types of operation.

As one expert – Dr Tim Chico, consultant cardiologist at the University of Sheffield in the UK – pointed out, if what this research suggests is shown to be correct, there would be major implications for the future scheduling of operations, and this could have extensive knock-on effects in terms of staffing and resources across the healthcare service.

That's why further study of this potential effect is very important to ensure we understand the reasons why these differences are seen and what types of surgery they may apply to. At present, this research alone does not answer enough questions to lead to a change in the way operations are organised.

If you have any concerns about an operation you're about to have, you should discuss them with your doctor.

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