Patients suffering from the most common form of heart rhythm disorder who are admitted hospitals over the weekend face a higher risk of dying over the next five years than those admitted during normal hours, a new study says.

This study by researchers involved National Health System hospitals, which is the publicly funded health system in the U.K., looked at 42,687 patients with atrial fibrillation (AF), one of the most common forms of abnormal heart rhythm. Atrial fibrillation raises the risk of heart-related death and stroke.

The study found that those admitted outside of normal operating hours (9 a.m. to  5 p.m,, Monday through Friday) have a 10 per cent increased risk of dying in the next five years. The research was adjusted to account for external factors that could influence death rates, such as age, gender, ethnic group, and the most common causes of mortality in the U.K.

Normally, the heart’s natural pacemaker sends out a regular electrical impulse that travels through the heart. But when someone has atrial fibrillation, impulses fire off from different places in the atria causing chaotic electrical activity, which makes them have an irregular, and sometimes fast, pulse.

The researchers also looked at 31,760 heart failure patients discharged from hospitals in the north of England at weekends, finding a 32 per cent increased chance of dying over the next five years compared to those sent home during regular weekday hours, a separate study found. Both were presented at the British Cardiovascular Science Study.

Although this study looked only at patients in the UK, other research has turned up similar findings about the so-called “weekend effect” in U.S., as well as other hospitals elsewhere in the world.