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| (c) Genetic Literacy Project |
A new study suggests patients undergoing open heart surgery in the afternoon have a lower risk of potentially fatal complications than those undergoing operations in the morning. The study found that events including heart attacks and heart failure were less common among those who had undergone a valve replacement operation in the afternoon. The finding appears to be linked to the ability of the heart tissue to recover after being starved of blood supply during surgery – an effect the researchers say is influenced by the cells’ biological or “circadian” clock.
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Writing in The Lancet, scientists report analysis from the outcomes in 596 patients, half of whom had valve surgery in the morning, and the other half in the afternoon. 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.
Doctors need to stop the heart to perform operations including heart valve replacements. This puts the organ under stress as the flow of oxygen to the heart tissue is reduced.
The team then randomly assigned 88 valve surgery patients to either morning or afternoon operations and monitored levels of a protein in their blood linked to heart tissue damage.
The results reveal that afternoon surgery patients had lower levels of the protein after their operation, suggesting about 20% less damage to the heart than those who underwent morning surgery.
Delving deeper, the team took biopsies from 14 morning surgery patients and 16 afternoon surgery patients, finding that tissue from the latter recovered better after being deprived of oxygen.
Further analysis found 287 genes within the cells that showed different levels of activity depending on whether the cells were from morning or afternoon patients – genes which have, in many cases, previously been linked to the circadian clock.
With a time-of-day effect also found in the recovery of mouse heart tissue, the team explored the impact of tinkering with the activity linked to one of the body clock genes, both using drugs and by looking at mice without the gene. Both approaches improved the recovery of the heart tissue at the time of day when it was typically worse.
It is known that the biological clock (circadian rhythm) is in every single cell of the body, therefore it affects the biological activity of each cell type. In healthy humans, the heart is known to follow a daily pattern of activity and is not at its optimum performance in the morning. It's health is already known to fluctuate over the course of a day. The risk of a heart attack or stroke is known to be highest first thing in the morning, while the heart and lungs work at their peak in the afternoon.
The study did not consider whether the surgeons performed the operation better in the afternoon, adding that more work was need to explore whether the findings would hold for patients at other hospitals, or for other types of surgery.
Why does this happen?
Scientists are associating the time of the surgery with the body’s biological clock. The heart tissue samples revealed nearly 300 genes linked to the circadian clock. They were more active in the afternoon than morning, as per the study.
Scientists hope to conduct more studies to confirm their results. They said they may even be able to develop medication that can alter the circadian clock in preparation for open heart surgery.
So what are the recommendations?
It is quite impossible for hospitals to schedule surgery in the afternoon. But one take-home from this study is to identify patients at highest risk, who will benefit from being operated later in the day. Obesity and type 2 diabetes have been shown to increase the risk of complications after surgery.
Thought: As an ophthalmic surgeon, I usually schedule cases that are likely to have better outcomes early in the morning, since we are supposed to be fresh to begin work. Obviously, this thought is anecdotal, since I have operated on equal number of cases with likely good visual outcomes later in the day, and they have had a good outcomes.
Most experts are of the opinion that though the study demonstrates value in scheduling cased in the afternoon, it is too premature to start doing that for every case. As mentioned above, high risk cases can be scheduled for the afternoon.
More and larger studies are required to confirm the outcomes from this one study, though there is data that precedes this study that indicates that the outcome of this study has some value.
References: The Lancet; The Guardian; BBC;
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