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Heart attack damage worse if experienced 6am and noon

Kathleen Blanchard's picture
Heart attack damage

Researchers have pinpointed the worse time to have a heart attack. A study shows heart damage is more extensive for people who suffer acute myocardial infarction (MI), known as STEMI, between 6am and noon. Scientists say circadian rhythm, the body's internal clock, affects the severity of a heart attack. In a study of 811 patients, researchers in Madrid, Spain determined a majority of patients who have a type of heart attack known as STEMI - ST segment elevation myocardial infarction – do so in the morning.

Morning heart attack damage the worse

The research team also found damage to the anterior portion of the heart tended to be larger, compared to other areas. In the study, 269 versus 240 patients had STEMI in the morning hours versus noon to 6pm; 161 had heart attack 6pm to midnight, and 141 between midnight and 6am.

The extent of damage that occurs to the heart muscle during a morning heart attack was based on a review of lab results that measures enzymes released into the bloodstream during a coronary event.

The study authors determined heart attacks are worse when they occur between dark to light hours, compared to STEMI that happens 6pm to midnight. Enzyme release that occurs when heart cells are deprived of oxygen and damaged is measurable with a blood test and tells physicians whether an MI is mild or severe.

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Past studies suggest morning heart attacks are more common, perhaps from excess activity and stress that accompanies the start of a busy day.

Findings published December 28 2004 in the Proceedings of the National Academy of Sciences also found a link to heart attack and circadian rhythm. The new study focuses on the severity of STEMI that happens in the morning.

The study, conducted by Kun Hu of Boston University, found fluctuations in heartbeat that peaked between 9am and 11am. The authors suggested heart attack occurs in the morning hours more frequently for individuals who are most vulnerable from risk factors.

The research included patients from Hospital Clinico San Carlos in Madrid, between 2003 and 2009. Based on cardiac enzyme results, heart attack damage was 21 percent worse for morning heart attack, compared to patients who had MI between 6pm and midnight.

Combined studies now show morning hours are more dangerous for experiencing a heart attack. New findings, published in the BMJ journal Heart, show damage to the heart muscle from STEMI tends to be worse in the dawn to light hours, compared to other times of day or night. The authors concluded circadian rhythms, or "oscillations" influence the amount of damage that occurs from a heart attack.

Heart doi:10.1136/hrt.2010.212621
"Circadian variations of infarct size in acute myocardial infarction"
Aida Suárez-Barrientos et al.