Stent patients generally take aspirin plus another anti-clotting medication for some time after the procedure - a year or more if they have drug-coated stents. So staying with your prescribed regimen is important, both Holmes and Tofler pointed out.

The findings are based on 124 patients treated at the Mayo Clinic for a stent blood clot between 1995 and 2009. Of those patients, 49 had an “early” clot - within 30 days of having the stent implanted - while 30 developed a clot within a year, and 45 more than one year later.

Only the risk of an early clot was elevated in the morning; later ones showed no clear circadian pattern.

That, according to Holmes, may be because early and late blood clots happen for different reasons.

The researchers were also able to pinpoint potential triggers of blood clots in some of the patients. About 6 percent had not been complying with their medication, and another 8 percent had infections or medical problems that could have either contributed to the clot or interfered with their medication regimen.

In addition, 11 percent of the patients said they’d been performing heavy exercise before their symptoms arose - something that is not advised.

“It is generally recommended that people not perform heavy exertion in the initial weeks after receiving a stent, since this may increase risk of stent thrombosis (blood clot),” Tofler told Reuters Health by email.

According to Holmes, the findings also raise the question of whether patients’ anti-clotting medication doses may be wearing off by the early morning - and whether it might be better to split the dose into two, taken in the morning and night.

Tofler, however, expressed doubts about that. The “duration of action” of both aspirin and clopidogrel (Plavix) - the anti-clotting drug commonly given to stent patients - is longer than one day, he said.

“So unless people weren’t taking those tablets when they should have been,” Tofler said, “timing should not have been a problem.”

SOURCE: Journal of the American College of Cardiology: Cardiovascular Interventions, February 2011.
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