A team of researchers recently published a study in The Lancet with their discovery of the association between the time of day and clinical outcome of open heart surgeries. Afternoon open heart surgeries are found to have fewer perioperative myocardial injuries (injuries before, during or after surgery). The finding, they say, has to do with our natural biological clock, known as the circadian rhythm.

The randomized study involved 596 aortic valve replacement patients observed for 500 days post-surgery in Lille, France. These patients were put in matched pairs; either having morning or afternoon surgeries. The results showed that the incidence of various perioperative cardiac events and injuries was lower in the afternoon group compared to the morning group, with a 50% lower risk of heart failure for the afternoon surgeries.

Further research was done to validate this finding with 30 tissue samples from patients of the trial. The afternoon surgery tissue samples were found to more quickly regain contractibility under conditions resembling blood flow throughout the heart. The researchers also discovered a difference of function in as many as 287 circadian rhythm-related genes between the two groups. A follow-up study with mice showed the deletion or suppression of a circadian rhythm-related gene, Rev-Erbα, reduced prevalence of injury during the sleep-to-wake transition in mice. This gene is found to be most active in the morning, so the reduction of this gene in the afternoon could reduce the risk of perioperative accidents.

These data show that afternoon surgeries might provide natural protection from myocardial injuries after open heart surgeries, leading to better outcomes of cardiac surgeries. Although many different factors lead to adverse injuries and complications after such complex surgery, this knowledge may be used to help patients with other exacerbating conditions, such as obesity and high blood pressure, that increase the risk for complications.