John O'Neill, from the United Kingdom medical research council's laboratory of Molecular Biology, said: "Scientifically it is not hugely surprising, because just like every other cell in the body, heart cells have circadian rhythms that orchestrate their activity". In addition, larger, randomized, multicenter trials could help validate their findings on the impact of surgery time and outcomes.
The researchers suggested that our hearts may be better equipped to deal with surgery in the afternoon as they may be stronger this time of day due to the impact of our body clock.
This has nothing to do with doctors feeling more exhausted in the morning, the study says. This showed that 54 out of 298 morning patients had adverse events, compared to just 28 out of 298 afternoon patients.
While 18% of morning surgery patients experienced a major cardiac event - such as a heart attack or heart failure -in the following 500 days, only 9% of those who had afternoon surgery experienced such events.
When disrupted - as with jetlag - repeatedly over long periods, it can aggravate depression, bipolar disorder, cognitive function, and memory formation, research has shown.
The new study unfolded in four steps.
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Dr Mike Knapton, associate medical director at the British Heart Foundation, said: "If this finding can be replicated in other hospitals this could be helpful to surgeons planning their operating list, for non-urgent heart surgery".
The latest study, published in The Lancet, chimes with previous research suggesting heart attacks that happen in the morning may be associated with a higher risk of the damage, compared to afternoon events.
"Medium-term postoperative cardiovascular morbidity remained lower in the afternoon than in the morning patients even after exclusion of perioperative myocardial infarction events and in the subgroup of patients who underwent isolated aortic valve replacement". However, patients who had afternoon surgery had lower levels of heart tissue damage after surgery, compared to morning surgery patients.
A genetic analysis of the same tissues showed hundreds of genes linked to circadian rhythms were more active in the afternoon group, suggesting that the heart, too, is influenced by our biological clock. They identified the Rev-Erbα gene "as a master switch in cardiomyocyte ischemia-reperfusion tolerance"-meaning by blocking or turning off its signaling pathway, the mice were able to recover from surgery after short sleep-to-wake transitions with fewer side effects".
Prof Staels said: "We believe we have identified a potential way to circumvent the disturbing observation that operations in the morning lead to more complications".