Most of us tend to think about a myocardial infarction (heart attack) as a pretty dramatic event -- and most of the time, it is. A heart attack is the most severe form of acute coronary syndrome (ACS), in which a coronary artery suddenly becomes blocked with a blood clot, which is usually caused by a sudden rupture of a plaque. With a heart attack, the blockage is severe enough to cause a portion of the heart muscle to die, and to become converted to scar tissue.
Most people who are having a heart attack know right away that something is very wrong. Typically, they experience severe chest pain or some other form of extremely oppressive chest discomfort. And while the pain or discomfort may be "atypical" (for instance, it may affect the neck, shoulders or back instead of the chest itself), it is usually quite difficult to ignore. Additional symptoms are often present, which may include breaking out into a cold sweat, shortness of breath, or a feeling of impending doom. In short, a heart attack is usually more than merely "noticeable" -- it is often as subtle as being hit in the face by a two by four.
So it may be surprising to hear that, for a substantial minority of people who have heart attacks, the heart attack is "silent." That is, the heart attack occurs -- a coronary artery is blocked by a blood clot and some of the heart muscle dies -- without the victim being aware that anything in particular is happening.
Why Are Some Heart Attacks "Silent?"There are several reasons why some people may have heart attacks without apparent symptoms. These include:
- Some people simply have high pain thresholds, or a very high tolerance for pain, and simply do not "notice" symptoms that would be difficult for the rest of us to ignore.
- Some medical conditions -- in particular, diabetes -- affect the nerves that carry pain impulses, so the symptoms of angina or a heart attack are blunted.
- In some people, cardiac ischemia (a lack of blood flow to the heart muscle) simply does not produce chest pain, or other "typical" symptoms of angina. Instead, they may experience shortness of breath, or transient weakness, or other non-specific symptoms that most people would not immediately relate to their heart. "Atypical" symptoms with cardiac ischemia are especially likely in women. (Read some of the unique features of CAD in women.)
- Some people -- especially when symptoms are relatively non-dramatic -- are simply very good at ignoring the signs and symptoms of a heart attack, and are able to brush them off as being due to a cold, or "something I ate."
When you add all these reasons up, it appears that about one out of five heart attacks turns out to be silent.
Can You Die From A Silent Heart Attack?You can die from any heart attack. While a reasonable argument can be made that once death occurs the heart attack can no longer be considered "silent," in many individuals with CAD the very first sign or symptom they experience from their condition is sudden death. Indeed, many people who die very suddenly, without any prior history of cardiac problems, in fact have significant CAD -- and most likely they experienced many episodes of "silent" ischemia, and possibly even silent heart attacks, prior to their fatal cardiac arrest.
How Are Silent Heart Attacks Diagnosed?Because a silent heart attack does not produce symptoms that send the patient to seek medical help, the diagnosis is only made after the fact -- after the damage has been done. Usually, the doctor is able to detect the cardiac damage that has resulted from the heart attack by examining an electrocardiogram. The diagnosis can be confirmed by performing an echocardiogram, in which the now-weakened heart muscle can be visualized.
What Does It Mean When A Silent Heart Attack Is Diagnosed?Once you are found to have had a silent heart attack, two important facts are now known about you. First, you have significant CAD. And second, your symptoms cannot be relied upon as a measure of how severe your CAD is, or how adequately it is being treated. That is, the absence of symptoms (such as angina) is not a reliable indicator that treatment is working, or that your CAD is stable.
If you have had a silent heart attack, your treatment should be the same as for any other person who has survived a heart attack -- treatment should be aimed at reducing the risk of a subsequent heart attack, preventing further ischemia, preventing the onset of heart failure, and preventing death from cardiac arrhythmias.
Also, since the presence or absence of angina cannot be relied upon as a measure of whether cardiac ischemia is being adequately treated, if you have had a silent heart attack your doctor should strongly consider asking you to have a stress test. The stress test can serve two important purposes in people who have had silent heart attacks. First, it may allow your doctor to measure the "threshold" of exercise that produces ischemia in your case. That is, your doctor may be able to give you specific instructions regarding which activities it is safe for you to perform. Since you cannot use the onset of angina as a warning that you are doing too much, this kind of advice can be very important.
And second, when ischemia occurs during a stress test, even people who have had silent heart attacks and/or silent ischemia will often feel "something," even if it is not typical angina. So the stress test can give important feedback to people with silent ischemia -- it can teach them that "this is what ischemia feels like in your case." In the future, whenever you experience "this" sensation -- whether it is mild discomfort in the shoulder, shortness of breath, sudden fatigue, or whatever it may be -- it means you are probably having an "angina equivalent," and you should immediately stop what you are doing, and follow your doctor's instructions for treating angina (for instance, taking a nitroglycerin tablet).
SummaryCAD -- even very significant CAD -- does not always produce the typical symptoms described in the medical textbooks. Cardiac ischemia and even heart attacks are fairly common in people who have never had symptoms suggesting CAD.
This means that if you have several risk factors for CAD -- such as smoking, living a sedentary life, being overweight, or having high cholesterol or hypertension -- the absence of symptoms should not be taken as proof that everything is fine with your coronary arteries. You should talk to your doctor about what you can do to reduce your high risk, before you suffer irreversible damage to your heart -- or worse.
Gibbons LW, Mitchell TL, Wei M, et al. Maximal exercise test as a predictor of risk for mortality from coronary heart disease in asymptomatic men. Am J Cardiol 2000; 86:53.
Gehi AK, Ali S, Na B, et al. Inducible ischemia and the risk of recurrent cardiovascular events in outpatients with stable coronary heart disease: the heart and soul study. Arch Intern Med 2008; 168:1423.