Does it matter what time you have a heart stent?

People who have procedures to unclog their heart's arteries in the morning may do better than those who have them in the afternoon, according to a new study.

Those who had the artery-clearing procedure known as angioplasty done in the afternoon were more likely to need it repeated, and less likely to be alive in a year, than those who had it done in the morning, the study team reports in the American Heart Journal.

But it's hard to tell if this was because of health differences in patients who had angioplasties at different times of day, or because of what happened during the actual procedures.

"From this study alone we can't definitively determine what the cause of those worse outcomes was," Dr. Warren Cantor, the lead author on the study and a cardiologist at Southlake Regional Health Centre in Newmarket, Ontario, told Reuters Health.

In an angioplasty, a small balloon is used to clear a blocked coronary artery - the artery that supplies blood directly to the heart - and a stent is inserted to keep the artery clear. Every year, more than 1 million people in the U.S. undergo angioplasty, a procedure with a price tag in the thousands of dollars. Others can rely on medication to prevent heart attacks, while some get more invasive bypass surgery, in which blood flow is diverted around a blocked artery to feed the heart.

While some angioplasties are emergency procedures, others are scheduled in advance to stop patients with heart disease from getting worse, or to relieve their symptoms.

Cantor and his colleagues looked at what happened to almost 2,500 patients that had non-emergency angioplasties in Alberta, Canada. A little over half of those patients had the procedure between 7 a.m. and noon, while the others had it between noon and 6 p.m.

Patients having an angioplasty in the afternoon tended to be worse off to begin with: they were sicker and had more advanced heart disease than patients who had angioplasty in the morning. It was unclear why the two groups had different characteristics, but patients who were already in the hospital - and therefore sicker, on average - were more likely to be scheduled in the afternoons.

They also were worse off after the procedure. Eighteen afternoon patients needed the angioplasty repeated or needed heart bypass surgery within the next month, versus 12 morning patients. After a year, 23 afternoon patients were dead, compared to 16 morning patients.

When they analyzed their data, the researchers found that pre-treatment differences probably weren't the only reason for this difference. Other explanations could be that doctors and nurses are more rushed or tired in the afternoon or watching patients less closely overnight. Patients with morning procedures would likely be more stable, and thus less vulnerable to complications, by the time the overnight shift started.