The odds of surviving cardiac arrest drop like the setting sun as day turns to night.
Cardiac arrest is always a medical emergency, regardless of the time of day. Mere seconds count. A new study, however, shows that the odds of surviving one fall during the night. And researchers aren’t exactly sure why.
Cardiac arrest occurs when the heart suddenly stops beating effectively, leading to death within minutes without immediate treatment. It is often caused by an electrical disturbance in the organ.
American researchers analyzed a national registry of 874,000 people who experienced cardiac arrest from 2013 to 2024. They examined arrests that occurred outside a hospital.
The team found that a cardiac arrest between 11 p.m. and 6:59 a.m. led to a 16% drop in the adjusted odds of surviving with good brain function. That’s compared with people whose hearts stopped during the other hours of the day.
The odds of death actually started increasing at 8 p.m., with the worst outcomes between 1 and 6 a.m.
What especially surprised researchers is that the odds haven’t really improved over the years, even as emergency medicine has gotten better.
Study authors thought slower ambulance response times at night might be to blame. In fact, response times are only a minute longer at night. While every minute counts, the study notes that this alone can’t fully explain the phenomenon.
Indeed, even when the arrest occurs with 911 responders already present, the nighttime penalty persists.
One way to reduce the risk of any heart trouble is to watch your diet and stay physically fit. It will also help you sleep soundly, whatever the hour.