Silent heart attacks. Half of all myocardial infarctions go unnoticed.

By Damien Mascret – Le Figaro

Silent myocardial infarctions, that is, those without symptoms, are perhaps much more frequent than doctors think. According to a North American study conducted in North Carolina involving 9500 middle-aged people (45 to 64 years old), in about fifteen years, almost as many myocardial infarctions (45%) go completely unnoticed as infarctions with symptoms (55%).

"We have known for a long time that there are silent and symptomatic heart attacks," explains Professor Jacques Blacher, cardiologist and head of the cardiovascular prevention sector at the Hôtel-Dieu (Paris), "but 45% seems like a lot to us, especially since they were identified based on repeated electrocardiograms (ECGs), and that is not the most efficient test for establishing a diagnosis of heart attack."

Projected pains

The same astonishment is expressed by Prof. Hervé Douard, head of the cardiology department at the University Hospital of Bordeaux, "we were expecting something like 20 to 30% of silent heart attacks, and many patients were excluded from the study, so we need to be careful."

In any case, classic "chest pain" isn't always the primary symptom and can even be absent. Four years ago, an analysis of over one million patients who suffered a heart attack in the United States between 1994 and 2006 showed that this symptom was absent in two out of three cases. And the pain can be "atypical"; doctors then refer to it as referred pain. Some people will feel pain in their arm or jaw, others in their stomach or back. This referred pain sometimes appears without the patient feeling chest pain.

"The intensity of the pain, as well as its eventual progression, is quite mysterious," observes Professor Douard. "Some will suffer terribly from a minor heart attack, while others will suffer almost nothing, even if they have had a serious heart attack!" In the North Carolina study, the problem is that 45% of the heart attacks that occurred were not identified when they happened. This is a real problem, because if the risk of death from cardiovascular causes is multiplied by five after a symptomatic heart attack, it is tripled after a silent myocardial infarction.

Identical risk factors

What makes Dr. Elsayed Soliman, from Wake Forest Medical School in Winston-Salem, who conducted the study published in the journal "Circulation," say that "the future is just as bleak after a silent myocardial infarction as after an infarction that manifested with symptoms"?

Perhaps a bit exaggerated? "Symptomatic heart attacks are generally larger than silent heart attacks," says Professor Blacher. Therefore, a priori, they are more worrying for the future. But "patients who don't know they've had a silent myocardial infarction may not have received the necessary treatment to prevent a recurrence," emphasizes Dr. Soliman.

"The risk would be to make people believe that silent myocardial infarction happens to them randomly," warns Professor Blacher, "but the risk factors are the same as for other heart attacks." And they are often neglected or underestimated by the population. "Half of the people who arrive at the cardiac ICU with a myocardial infarction had never had symptoms before!" specifies Professor Jacques Blacher.

In any case, this study explains why half of people with coronary artery disease discover it after having a myocardial infarction.

"There's no need to worry everyone," reassures Professor Douard, "the frequency of heart attacks is only 0,3% in the North Carolina study."