According to Madrid researchers, myocardial infarctions occurring at night cause on average less heart damage than those during the day. The cause: reduced activity of certain inflammatory immune cells, subject to the circadian rhythm. A promising discovery, but to be interpreted with caution, recalls Dr Gérald Kierzek.
Are nocturnal heart attacks really less serious?
Every year, nearly 80,000 heart attacks occur in France. Their severity varies depending on many parameters: extent of the coronary obstruction, speed of treatment, state of health of the patient… But also, according to a new study, the time of day when the infarction occurs.
Researchers from National Center for Cardiovascular Investigations (CNIC) of Madrid suggest that heart attacks occurring at night are associated with less serious heart damage. Their work was published in the
Journal of Experimental Medicine.
Heart attack: when inflammation worsens the damage
During a heart attack, the lack of oxygen linked to the obstruction of a coronary artery is not the only one responsible for the damage suffered by the heart. The inflammatory reaction triggered by the immune system plays a major role.
Scientists point out that almost half of post-infarction heart damage is due to the action of neutrophils. White blood cells responsible for cleaning damaged tissues.
In situations of acute stress, these cells can cause significant collateral damage to healthy heart muscle.
At night, less aggressive immune cells
The human immune system is subject to the circadian rhythm, which alternates phases of activity and rest over 24 hours. At night, when the body sleeps and the risk of infection is lower, certain immune responses are voluntarily attenuated.
To understand the impact of this phenomenon on heart attacks, researchers analyzed data from thousands of patients at the 12 de Octubre Hospital in Madrid. Their results show that:
- At night, neutrophils migrate to the specific damaged area of the heart, while sparing healthy tissues;
- During the day, they lose this precision, causing more diffuse and more harmful inflammation.
“At night, neutrophils are more directional and cause less damage to surrounding tissues,” explains Dr. Alejandra Aroca-Crevillén, first author of the study.
Could cheating the biological clock protect the heart?
Secondly, the Spanish team therefore tested an innovative approach: a compound capable of mimicking a biological factor produced mainly at night.
This mechanism would “trick” neutrophils into believing that it is night, thus reducing their excessive inflammatory activity during the day. The trials showed better protection of the heart muscle, without altering the overall immune response against infections. Far from being trivial, these results could open the way to new therapeutic strategies based on chronobiology, potentially applicable to other organs.
A study to be interpreted with caution for Dr Gérald Kierzek
For Dr Gérald Kierzek, emergency doctor, these conclusions must however remain conditional.
Nocturnal heart attacks could actually cause less serious inflammatory damage, due to reduced neutrophil activity linked to the circadian rhythm.
However, the doctor recalls that morning heart attacks remain the most severeand that these observational data must still be confirmed before any clinical application.
Can you die of a heart attack at night? Yes, without a doubt
Although cardiac damage may be less at night in certain cases, the vital risk remains real.
Certain situations even considerably increase the danger of nocturnal heart attacks:
- In patients suffering from sleep apnea syndrome, the risk of sudden cardiac death increases at night. 46% of deaths occur between midnight and 6 a.m., compared to 16% in the general population.
Nocturnal hypoxemia and heart rhythm disturbances are the main causes; - Pickup times may be longer at night. Due to minimized symptoms or hesitation to call for help.
Whether the time matters or not, intense chest pain that suddenly wakes you up during the night should prompt you to do just one thing: call immediately on the 15th, without waiting for the morning.