A recent study from the University of Manchester reveals that heart operations starting in the late morning carry a slightly higher risk of death. The research, published in the journal Anaesthesia, analyzed data from over 24,000 patients across England, Wales, and Northern Ireland. It found that heart surgery performed in the late morning was linked to an 18% higher risk of cardiovascular mortality compared to operations scheduled for early morning.^[1][2][3][4] ### Body Clock Influences Surgical Outcomes Researchers believe the body's natural 24-hour cycle, known as the circadian rhythm or body clock, plays a key role in these outcomes. This internal clock affects various biological processes in our cells and organs. The study accounted for different complexities and durations of surgery, confirming the link between timing and mortality risk.^[1][2][3][4] Dr. Gareth Kitchen, a Clinical Senior Lecturer at The University of Manchester and lead author, explained the findings. "This research shows a slightly higher risk of heart related mortality is likely to occur when heart surgery starts in late morning," he said.^[1][2] He added that while the risk is statistically significant, it remains relatively modest. "Patients can be reassured that most people will almost certainly be unaffected," Dr. Kitchen told reporters.^[1][2] Still, he emphasized the duty of clinicians to ensure the best possible outcomes, suggesting that adjusting surgery timings could be an inexpensive way to achieve this.^[1] The most common surgical start time was early morning, between 7:00 AM and 9:59 AM, accounting for 47% of all surgeries.^[1][2] Late morning surgery was defined as starting between 10:00 AM and 11:59 AM.^[1] The study did not find that complication rates or readmissions were affected by the time of day.^[1][2][3] ### Afternoon Operations Show Better Results These new findings align with previous international research suggesting that the time of day influences heart surgery outcomes. An earlier study from 2017, conducted by researchers at the University of Lille in France and published in The Lancet, also pointed to the body clock's impact.^[5][6][7][8] That study found that patients undergoing open heart surgery in the afternoon had a lower risk of serious complications, such as heart attacks and heart failure, compared to those operated on in the morning.^[5][6][7] Professor David Montaigne, first author of the French research, stated that post-surgery heart damage was more common among morning surgery patients.^[6][8][9] His team observed that 18% of morning surgery patients experienced a major cardiac event within 500 days, compared to only 9% of those who had afternoon surgery.^[5] This suggested a 50% lower risk of major cardiac events for afternoon operations.^[6][8] The French study also investigated why this difference occurs. They found that heart tissue from afternoon surgery patients recovered better after being deprived of oxygen during the operation.^[5][6] Genetic analysis revealed that 287 genes linked to the circadian clock showed different activity levels depending on whether the tissue samples were from morning or afternoon patients.^[5][6][8] This suggests that the heart's ability to repair itself might be weaker in the morning.^[6][8] "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," Professor Montaigne said.^[6][8] ### Future of Personalized Surgery The combined evidence from these studies raises important questions about the best time to schedule heart surgery. While the risks identified are modest, even small improvements in outcomes can benefit many patients, especially given that over 25,000 heart operations are performed in the UK each year.^[1][3] Integrating body clock biology into surgical planning could lead to more personalized medicine. Researchers are exploring ways to understand how individual body clocks vary, as some people are "early birds" and others are "night owls."^[2][4] This understanding could eventually allow for precision scheduling of cardiac surgery to achieve better patient outcomes.^[2] Further research might also explore developing drugs that can influence circadian clock-related genes. These medications could potentially protect the heart from damage during surgery, regardless of the time of day.^[6][7][8] For now, the studies suggest that considering the time of day for non-emergency heart procedures could offer a simple, cost-effective way to slightly improve patient safety.

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