There’s no good time to have a heart attack, but having one at night or on a weekend may mean getting slower hospital care and facing an increased risk of death, a new international study shows.

The study published in the British journal BMJ, is not the first to find this gap, but it is the largest, collecting data on nearly 2 million patients from 48 previous studies in the U.S., Canada and Europe. It finds heart-attack patients who arrive at hospitals on nights or weekends are about 5 percent more likely to die, either immediately or in the next 30 days, than those who arrive on a weekday.

One possible explanation: Off-hours patients with severe heart attacks wait an average of 15 minutes longer than weekday patients for a crucial procedure called angioplasty that opens up clogged arteries, the study finds. They are 40 percent less likely than weekday patients to have the procedure during the 90-minute window considered ideal, researchers say.

The most likely explanation for the higher death rate is hospitals provide worse care in off hours, said study co-author Atsushi Sorita, a senior fellow in preventive medicine and public health at the Mayo Clinic in Rochester, Minn.

“We know hospitals have fewer staff and resources during off-hours,” he said. “They need to think about the system and provide care that is consistent 24 hours a day, seven days a week.”

Hospitals have been under pressure to speed up “door to balloon times,” the time from when a heart-attack patient arrives to when a balloon is inflated in a blocked artery during angioplasty. The study found no evidence the push had improved the off-hours death gap during the years in which data for the various studies were collected, 1987 to 2011.

“The differences in mortality seem to be increasing,” Sorita said. “That seems surprising.”

The findings about heart attacks are consistent with findings about other conditions treated by hospitals in off-hours, said Chaim Bell, a general internist at Mount Sinai Hospital in Toronto, who wrote an editorial accompanying the study. The exception, he said, is intensive care, where patients appear to get consistent care regardless of the day or time.

The problem is not just that hospitals have fewer people on duty on nights and weekends ... “There may be less senior people there on weekends and fewer supervisors,” Bell said.

He said the study has limitations. It pools studies from various geographic areas using differing statistical methods and defined off hours in differing ways. He said it is notable the care gap seems to exist in so many countries with differing standards of care.

The studies do not provide the strongest kind of evidence, in which patients are randomly assigned to get care at one time or another because that would be both unethical and impractical in heart-attack patients.

It’s important patients not misinterpret the study as a reason to avoid hospitals on weekends or nights if they think they are having a heart attack, Sorita said – since the whole point is speed is crucial.

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