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Cardiologists For this reason, heart attacks are more dangerous in the morning
Heart attacks are generally a life-threatening event. However, the chances of recovery after an infarction have largely depended on the time of day of the event, according to a recent study by scientists from the Ludwig Maximilian University (LMU) in Munich. In the morning heart attacks are therefore particularly dangerous.
Heart attacks are among the leading causes of death in modern industrial nations. Earlier epidemiological studies had already shown that myocardial infarction ("medical term for heart attack") occurs "more often in the morning and is associated with a worse outcome in terms of mortality and recovery," the research team led by Prof. Sabine Steffens from the Institute for Epidemiology and prophylaxis of circulatory diseases at the LMU Hospital. In their current study, the scientists have now investigated which effect underlies the relationship between the risk of heart attack and the time of day. The results of the study were published in the journal EMBO Molecular Medicine.
In the morning, the risk of a heart attack is particularly high and the chances of recovery are significantly worse. (Image: michaeljung / fotolia.com) Inflammatory response varies throughout the day
The researchers confirmed in their study on mice that it depends on a heart attack from the time of day, as the inflammatory reaction in the affected heart muscle proceeds. They also found that "the strength of the immune response and thus the recruitment of neutrophil granulocytes to the site of inflammation fluctuates throughout the day," said the LMU. Of decisive importance for this is the chemokine receptor CXCR2, whose activity is influenced by the biorhythm. Study leader Prof. Steffens and colleagues were able to demonstrate in the mouse model that the influx of neutrophils into the damaged heart muscle also depends on the biorhythm. Thus, the immune cells, about one hour after the active phase has begun, triggered a stronger inflammation than during the sleep phase or later in the day.
Neutrophil granulocytes crucial for the inflammatory response
The death of heart muscle cells in a heart attack alerts immune system cells and sends them to damaged tissue. These so-called neutrophilic granulocytes trigger an inflammatory reaction in the course of which the dead tissue is broken down by immune cells. The important function of neutrophils for the healing process had already been proven by Prof. Steffens in previous studies. However, this only applies as long as the immune reaction is in equilibrium and the neutrophils do not occur in too large an amount.
Decrypted molecular mechanism
Which molecular mechanism increases the risk of having a heart attack early in the morning and determines the relationship between the time of day and the chances of recovery has remained unclear. In their current study, LMU researchers have now shown that "more neutrophils are released from the bone marrow at the beginning of the active phase". This active phase lies with most people in the early morning hours, reports Prof. Steffens. "A heart attack at this time leads to an excessive inflammatory response by neutrophils," Steffens continued. As a result of the increased inflammation, according to the expert also more scars form in the tissue and the heart muscle expands more, which additionally weakens the heart.
New therapeutic options?
In their investigations, the scientists were also able to prove that the chemokine receptor CXCR2, which sits on the cell surface of the neutrophils, also works depending on the time of day. "The strongest he is expressed directly after waking up," said the LMU. If the receptor is suppressed by a drug, the inflammation and thus the damage to the heart muscle has been significantly reduced. "Our study shows that the time of day plays an important role in the treatment of a heart attack, and that CXCR2 may be an interesting therapeutic target if too many neutrophils migrate into the damaged muscle tissue after a heart attack," says Prof. Steffens. (Fp)