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Journal of the American College of Cardiology

News & Views

CST influenced by circadian rhythms

Circadian rhythms affect the incidence of coronary stent thrombosis (CST), with more events occurring during the early morning hours, according to research(1) published recently in JACC: Cardiovascular Interventions.

A research team from the Mayo Clinic, Rochester, conducted a retrospective analysis of 124 patients who underwent repeat percutaneous coronary intervention in a previously stented coronary artery segment between February 1995 and August 2009.

Onset of stent thrombosis was significantly associated with time of day (p=0.006), with a peak incidence around 7:00 AM. When patients were subdivided into early stent thrombosis (0 to 30 days; n=49), late stent thrombosis (31 to 360 days; n = 30), and very late stent thrombosis (>360 days; n=45), only early stent thrombosis remained significantly associated with time of day (p=0.030). No association with the day of the week was found (p=0.509); however, onset of stent thrombosis did follow a significant seasonal pattern, with higher occurrences in the summer months (p=0.036).

In search of potential triggers, the team was able to establish the physical activity level prior to stent thrombosis onset in 62 patients. Of these patients, 33.9% were sleeping, 25.8% were lying or sitting, 29.0% were engaged in light-to-moderate physical exertion, and 11.3% were engaged in heavy physical exertion. Other medical conditions were also identified as possible triggers among the full 124-patient study sample, including medication noncompliance (5.6%), hospitalization for surgery or invasive diagnostics (4.0%), and acute infections (4.0%).

According to the authors, “several physiological processes” may contribute to the increased rate of stent thrombosis in the morning hours. These include hypercoagulability and hypofibrinolysis during this time; a higher activity level of the renin-angiotensin-aldosterone hormone system between 6:00 am and 8:00 am, which causes higher blood pressure and heart rate; a higher degree of blood viscosity in the morning, which is magnified by sitting upright after a night of supine sleep; and lowered levels of antithrombotic medication in the morning just before the patient awakens and takes a new dose.

The lack of an association between stent thrombosis and day of week—which is unlike other adverse cardiac events, such as AMI, in which higher occurrences have been found on Monday—may suggest that mental stress from employment plays a more limited role in stent thrombosis, the researchers said. They also surmised that a higher rate of stent thrombosis in the summer months may be attributed to patients’ higher activity level in warm weather.

While the authors admit there has been a decreasing incidence in stent thrombosis across recent years—largely because of dual antiplatelet therapy and improved stent design—they add that the consequences of this adverse event remain severe, and that the study’s conclusions may help improve outcomes “by optimizing medical treatment during high-risk intervals throughout the day, week, and year”.

“The most practical implication of these study results is that it may be of benefit for patients with coronary stents to take their antithrombotic medication in the evening (rather than in the morning) to prevent nadir levels of medication during the hazardous morning hours,” said study author Karim Mahmoud.


  1. Mahmoud KD, Lennon RJ, Ting HH, Rihal CS, Holmes DR. Circadian Variation in Coronary Stent Thrombosis. JACC: Cardiovascular Interventions 2011;4;183-90

Published on: March 3, 2011

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