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Understanding why heart attacks are more common in early morning

Robin Wulffson MD's picture
heart attack, ventricular fibrillation, sudden death, circadian rhythm, KLF15

Numerous studies in the medical literature have reported that heart attacks are five to six times more likely to occur in the early morning hours between 1 a.m. and 5 a.m. Studies also note that heart attacks occurring during these hours are often more severe than those that occur later than the day.

These heart attacks are often due to a condition known as ventricular fibrillation in which the ventricles (pumping chambers of the heart beat rapidly and ineffectively in an uncoordinated manner. Various theories have been proposed for this phenomenon, including the stress of having to rise and go to work in the morning.

A new study offers a biological explanation for this cluster of adverse events. The researchers are affiliated with various renowned medical institutions in the US, such as Baylor College of Medicine (Houston, Texas) and Case Western Reserve School of Medicine (Cleveland, Ohio). They published their findings online on February 22 in the journal Nature.

Using a mouse model, the researchers uncovered a molecular basis for this occurrence. The bodily process of all mammals is governed by a 24 hour cycle known as the circadian rhythm. Various hormonal levels fluctuate during this cycle and govern when we are more likely to sleep and being alert. The circadian rhythm explains why, when we travel to a different time zone, we have trouble sleeping during a period of wakefulness at our old location.

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Due to circadian rhythm, levels of a protein known as KLF15 fluctuate throughout the day. The researchers found that either a too low or too high level of this protein produced a cascade of events, which altered the potassium current in heat muscle. This change in turn impacted the electrical recovery time of the heart muscle. Study author Dr. Xander Wehrens, professor of medicine in the department of cardiology at Baylor College of medicine, explained “This time interval is critical. Too long or too short of an interval can result in abnormal heart rhythms called arrhythmias. As the heart loses the regularity of the beat, it cannot pump blood efficiently and a person can die suddenly."

The practical application of this research is that a thorough understanding of this mechanism could lead to new therapies to control the levels of KLF15. Before that can be accomplished, the studies need to be repeated in humans.

Take Home Message:
This research may lead to new treatments that can reduce the risk of sudden death from an early morning heart attack. However, stress also plays a role in a cardiac event because it increases the levels of hormones such as epinephrine, which increase the heart rate and blood pressure. Thus, managing stress can reduce the risk of a heart attack. Of significant importance is a healthy lifestyle, which excludes smoking and other harmful activities as well as incorporating a healthy diet and regular exercise program into one’s daily routine.

Reference: Nature

See Also: Unhealthy lifestyle accelerates cellular aging, resulting in heart attacks