The time of day of surgery may have long-term impacts on the health of patients. Looking at how the circadian rhythm affects the outcomes of surgery, researchers are claiming that patients who undergo major heart surgery in the afternoon may walk away with reduced perioperative myocardial injury and postoperative morbidity compared to patients who were operated on earlier in the morning1.

Afternoon heart surgery slashes risk of major adverse cardiac event by 50%

Over six years, the team looked at nearly 600 patients, half who received aortic valve replacement surgery in the morning while the other half underwent the same surgery in the afternoon. Interestingly, in the subsequent 500 days after surgery, they found that the latter group were 50% less likely to experience a major adverse cardiac event – such as myocardial infarction, acute heart failure, or death.

These findings were backed up by experiments on tissue samples taken from a randomised controlled trial of 88 of the patients in the same study. Atrial myocardial cells from patients in the afternoon group were found to be less damaged and were able regain contractility quicker than their morning counterparts when subjected to surgical stress re-created in the laboratory.

Experts say this sort of heart tissue injury affects mortality rates.

Intrinsic cardiac biorhythm may be behind the stark differences in response

Researchers went one step further and analysed the gene expression in myocardiocytes of a subgroup of 30 patients from the randomised controlled trial. They discovered that 287 genes were expressed differently based on the time of day. These time-sensitive changes in gene expression support the hypothesis of an intrinsic cardiac biorhythm, which could explain the variations in tissue behaviour.

Furthermore, knowledge of the role of genetics in the circadian rhythm creates avenues for possible gene-based therapy. One gene in this study, Rev-Erbα, was observed to have the most dynamic change between dawn and noon. Experiments on mice with suppressed Rev-Erbα gene function resulted in an increased tolerance to cardiac stressors.

“One could imagine, quite rapidly, a pharmacological approach that could basically wipe out the effects between morning and afternoon,” said Professor Bart Staels, one of the study’s authors.

Treatment efficacy has long been thought to be influenced by the body’s intrinsic circadian rhythm. Known as chronotherapy, previous evidence has proven that chemotherapy and flu vaccinations may work better when administered at certain times of the day3.

“This study underscores the importance of the circadian rhythm biology that’s finally starting to gain recognition in science,” said James Olcese, a biomedical sciences professor at Florida State University’s College of Medicine who was not involved in the study2.

“This could potentially save a lot of lives. It’s pretty critical, taking it beyond a basic concept of tissue all the way to the real-world scenario of surgeries occurring at different times of day.”

Does this mean limiting surgeries to the afternoon?

While the study focuses on heart surgeries only, a separate Canadian study found that the risk of mortality was doubled in patients who were operated on during the night. It attributes this to healthcare provider fatigue during later times of the day. The same study put forth that not operating at all may be better than performing emergency procedures while fatigued.

Sleep deprivation is worryingly common amongst healthcare providers. Working tired leaves more room for mistakes – and mistakes in medicine are often dangerous.

"The basic take-home is that fatigue decreases safety," said Bryan Vila, a sleep expert at the Washington State University–Spokane, United States. Learning healthy sleeping practices is "just as important as occupational training," he said4.

While it is unfeasible to limit surgery to being performed only in the afternoon, these findings take us one step closer to reducing mortality rates in patients undergoing high-risk surgery. MIMS

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