Having a heart attack at night or during the weekend could raise your risk of death.

Heart attacks that occur outside of regular hospital hours could contribute to thousands of preventable deaths every year, a British Medical Journal news release reported.

The researchers found there was a longer "door to balloon time" (a procedure that inflates the artery) after regular hospital hours.

About 400,000 die from coronary heart disease in the U.S. every year and a million suffer heart attacks. Cardiovascular events are the leading cause of death worldwide.

This study was the first to take a close look at heart attacks that occur on the weekends and during nighttime hours and how they are linked to higher mortality rates.

The research team looked at data from 48 studies that encompassed 1,896,859 patients. The team took into account differences of "type and quality" of the studies in order to eliminated bias.

The researchers concluded those who presented during off-hours (including weekends) had about a five percent higher risk of death that lasted up to 30 days after discharge than those who presented during regular business hours. This contributed to about 6,000 U.S. deaths every year.

The team found that for the certain types of heart attacks ("ST elevation myocardial infarction or STEMI") there was about a 15 minute delay in door to balloon time during off-hours.

"[This] could increase mortality by as much as 10 [to] 15 [percent], assuming linearity between door to balloon time and mortality," the authors said, the news release reported.

The researchers cannot completely rule out other factors associated with patient characteristics as the underlying cause, the link between mortality and hospital off-hours is strong.

"Increased mortality during off-hours is associated with factors that arise after presentation at hospital," the authors said.

In the future the researchers hope to look at how quality of care varies during on and off hours, including number of staff and quality of doctors.

"Experience delays in urgent care and worse outcomes, and the gap seems to be increasing over time, "an editorial from the University of Toronto said, according to the news release. 

"[Healthcare manangers] should focus on improving their off-hour care, with the goal of providing consistently high quality care 24 hours a day and seven days a week. [Future studies] should try to identify specific deficits in the care pathway during off-hours, allowing differences in outcomes to be linked to differences in processes," the researchers suggested.