Late Night Heart Attacks More Severe

There may be no way to predict when a heart attack will strike, but new research suggests that the day of day may indicate the severity. Late night heart attacks appear to be most devastating.

Heart attack size and the function of the heart's left ventricle appear significantly different based on the time of day. Patients who have heart attacks between 1 a.m. and 5 p.m. appear to fare worse.

Call 911 immediately if you have symptoms of a heart attack.

Previous research suggested a similar finding in rodents, but it was unclear as to whether humans would be affected by time in the same way.

Study senior author Dr. Jay H. Traverse, a cardiologist at the Minneapolis Heart Institute at Abbott Northwestern Hospital and physician researcher with Minneapolis Heart Institute Foundation, initiated the research to determine whether the time of day a heart attack occurs impacts the amount of damage the heart sustains, or whether it was simply a phenomenon in rodents.

Researchers retrospectively studied 1,031 patients hospitalized for a heart attack or who were referred for angioplasty to unclog blocked arteries. They identified 165 patients who suffered a first heart attack, at least partially as a result of clogged arteries.

The 165 patients had well-documented onset times, and recorded data indicating the size of the heart attack based on cardiac MRI imaging and the area of the heart at risk.

Investigators found that the extent of heart injury was significantly associated with the time of day of the onset of heart attack symptoms. During the peak heart attack severity period of between 1 a.m. and 5 a.m., patients who had heart attacks suffered 82 percent more injury to the heart as compared to the lowest recorded times of injury.

"It is important to understand that the heart's ability to protect itself against more severe damage varies over a 24-hour cycle. Identifying those protective changes may be particularly relevant for pharmaceutical manufacturers that are seeking to develop cardioprotective drugs," Dr. Traverse said.

The study was recently published in Circulation Research.