Hospital patients who suffer cardiac arrest may be more likely to die if it happens in the middle of the night or on a weekend than if it occurs on a weekday, and researchers are trying to figure out why.

Dr. Julia Indik is with the Sarver Heart Center at the University of Arizona in Tucson. She was asked to write the commentary on the study. She says researchers could not identify a reason for the gap in survival rate.

“Everything they looked at ending up not being the cause of the gap. So, we don’t have an answer for that question. And we do need to look further," Indik said.

Researchers examined data on more than 150,000 adults who had a cardiac arrest between 2000 and 2014. Twenty-one percent of “on-hours” cardiac arrest patients survived until discharge. Seventeen percent of “off-hours” patients survived.