Outcomes for open heart surgery could potentially be improved by moving surgery to the afternoon, rather than in the morning, according to French researchers.
Their study, published in The Lancet, identified a link between a person’s circadian clock and their risk of heart damage and major cardiac events after heart surgery.
“Heart damage is more common among people who have heart surgery in the morning”
The study also provides early insights into the mechanism behind this link, identifying nearly 300 genes linking the circadian clock to heart damage.
The research consisted of four parts – an observational study, a randomised controlled trial, a human tissue analysis and a mouse model to further investigate biological mechanisms.
In the observational study, researchers tracked 596 people who had heart valve replacement surgery for 500 days to monitor for any major cardiac events, such as a heart attack, heart failure or death.
Patients who had surgery in the afternoon had a 50% lower risk of a major event than those in the morning – equating to one major event avoided for every 11 patients who had afternoon surgery.
In the trial section, 88 patients were randomly scheduled for heart valve replacement surgery in the morning or afternoon and their health was monitored until they left hospital.
“One might propose that high-risk patients should preferentially be operated on in the afternoon”
There were no deaths in either group and the average time in hospital was 12 days. But afternoon patients had lower levels of heart tissue damage after surgery, compared to morning patients.
The researchers then tested 30 heart tissue samples from a sub-group of trial patients – 14 from the morning group and 16 from the afternoon. Tests suggested the afternoon samples more quickly regained their ability to contract when put in conditions replicating the heart refilling with blood.
A genetic analysis of these samples also showed that 287 genes linked to the circadian clock were more active in the afternoon surgery samples, compared to the morning surgery samples.
To further understand the mechanism, the researchers deleted and replaced the relevant genes in a mouse to study how this affected the sleep-to-wake transition.
Lead study author Professor David Montaigne, from the University of Lille, said: “Our study found that post-surgery heart damage is more common among people who have heart surgery in the morning, compared to the afternoon.
“Our findings suggest this is because part of the biological mechanism behind the damage is affected by a person’s circadian clock and the underlying genes that control it,” he said.
“As a result, moving heart surgery to the afternoon may help to reduce a person’s risk of heart damage after surgery,” he added.
Commenting on the study, Professor Michel Ovize, from the Hôpital Louis Pradel, said it had “clearly shown” that circadian rhythm was of clinical importance in aortic valve replacement surgery.
“Even before we have drugs available to regulate the circadian clock, one might propose that high-risk patients should preferentially be operated on in the afternoon,” he said in a linked comment.
Dr Michael Knapton
Dr Mike Knapton, associate medical director at the British Heart Foundation, said: “The time of day appears to be a significant factor in the outcome from surgery, with better outcomes if your surgery is in the afternoon.
“If this finding can be replicated in other hospitals this could be helpful to surgeons planning their operating list, for non-urgent heart surgery,” he said.
“The study also suggests that modifying the genes responsible for this phenomenon could lead to the development of new drugs to protect the heart from damage during open heart surgery,” he added.