A study at Cedars-Sinai Medical Canter has found that during nighttime hours, women might be more likely than men to suffer sudden death due to cardiac arrest, the hospital reported Wednesday.

“Dying suddenly during nighttime hours is a perplexing and devastating phenomenon,” said Dr. Sumeet Chugh, senior author of the study and director of the Center for Cardiac Arrest Prevention in the hospital’s Smidt Heart Institute. “We were surprised to discover that being female is an independent predictor of these events.”

According to Chugh’s findings, 25.4% of females studied suffered cardiac arrest at night versus 20.6% of their male counterparts.

Sudden cardiac arrest is an electrical disturbance of the heart rhythm that causes the heart to stop beating. People often confuse it with a heart attack. However, a heart attack is caused by a buildup of cholesterol plaque that creates a blockage in the coronary arteries. And unlike a heart attack, when most have symptoms, sudden cardiac death can occur without warning signs.

Another major difference: Most people survive heart attacks, but only 10% of patients survive cardiac arrest when it occurs outside a hospital.

Of the approximately 350,000 people affected by the condition each year in the United States, roughly 17% to 41% of cases occur during the nighttime hours of 10 p.m. to 6 a.m. Chugh and his team of investigators looked at records of 4,126 patients, with 3,208 daytime cases of sudden cardiac arrest and 918 nighttime cases. Compared with daytime cases, patients who suffered from nighttime cardiac arrest were more likely to be female.

Chugh said medical experts are puzzled over the findings because during the late hours, most patients are in a resting state, with reduced metabolism, heart rate and blood pressure.

Also among the findings: The prevalence of lung disease was significantly higher in those who had a cardiac arrest at night compared with those who had cardiac arrest during the daytime. Those who had cardiac arrests in the nighttime also had a higher prevalence of prior or current smoking history.

“The prevalence of chronic obstructive lung disease and asthma were found to be significantly higher in sudden cardiac arrest cases at night compared with daytime cases, regardless of gender,” Chugh said. “Brain-affecting medications, some of which have the potential to suppress breathing, were also found to have a significantly greater usage in nighttime compared to daytime cardiac arrest.”

The findings suggest that physicians may wish to be cautious when recommending brain-affecting medications, for example, sedatives and drugs prescribed for pain and depression management, to high-risk patients, especially women.

“This important research may better guide physicians and the broader medical community to making more sound, science-backed recommendations in treating this difficult condition,” said Dr. Christine Albert, chair of the department of cardiology in the Smidt Heart Institute. “It is also a necessary continuation of sex-based research defining much of the field of cardiology.”

The study was published Tuesday in the journal Heart Rhythm, and can be read at www.heartrhythmjournal.com/article/S1547-5271(21)00036-9/fulltext.

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