Why Are Some Heart Attacks Silent?

Myocardial Infarctions Without Apparent Symptoms

Heart attack
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A silent heart attack is a heart attack that happens without causing noticeable symptoms — or at least, without causing symptoms so severe that the victim cannot ignore them. The diagnosis is made retrospectively, when evidence of a myocardial infarction (heart attack) is found on an electrocardiogram in a person without a clinical history of having had a heart attack. Usually, these people are diagnosed when they are seeing a doctor for a completely unrelated reason.

When the diagnosis of a prior heart attack is finally made, typically both the patient and the doctor are surprised.

Overview

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 usually occurs when an atherosclerotic plaque in one of the coronary arteries ruptures. The rupture causes a blood clot to form in the artery, leading to an acute blockage. The heart muscle being supplied by the blocked artery immediately becomes ischemic (starved for oxygen), which typically leads to chest pain or other alarming symptoms. Unless the blockage is relieved within a few hours, the ischemic heart muscle dies. It is the death of a portion of heart muscle that constitutes a heart attack.

Most often, the symptoms caused by a blocked coronary artery are severe enough that most people having this problem quickly seek medical help. However, it is not uncommon for people to suffer myocardial infarctions without noticing symptoms that compel them to see a doctor. 

Current estimates are that about 20% of heart attacks go undetected until some time after the event is over. The problem, of course, is that acute therapy cannot be given if everyone is unaware that a heart attack is occurring, and rapid therapy is critical if the amount of heart muscle damage caused by a heart attack is to be minimized.

Signs and Symptoms Of a “Typical” Heart Attack

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.

Why Are Some Heart Attacks Silent?

Given these usual symptoms, 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.

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.
  • Certain medical conditions — especially diabetes and chronic kidney disease — can affect the nerves that carry pain impulses, so the symptoms of angina or a heart attack are blunted.
  • In some people, cardiac ischemia may simply produce atypical symptoms.Instead of experiencing angina, for instance, they may experience dyspnea (shortness of breath), 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.
  • 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, heartburn, or "something I ate."
  • Age and sex are associated with silent heart attacks. Heart attacks are more likely to be silent in older people, especially those over 75. They are also seen more commonly in men than women.

    When you add all these reasons up, it appears that about one out of five heart attacks turns out to be silent.

    Prognosis and Fatalities

    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 quite likely they experienced many episodes of "silent" ischemia, and possibly even silent heart attacks, prior to their fatal cardiac arrest.

    People who appear well but are diagnosed with silent heart attacks appear to have a somewhat worse long-term prognosis than people whose heart attacks were diagnosed and treated promptly. The increased risk is probably related to the high prevalence of diabetes or kidney disease in these people, their commonly advanced age, and the fact that subsequent episodes of cardiac ischemia are also likely to be “silent,” and thus are unlikely to be treated promptly.

    Diagnosis 

    Because a silent heart attack does not produce symptoms that cause the victim to seek medical help, the diagnosis is only made after the fact — after the damage has been done. At some point in the future, a doctor typically will notice that heart damage has occurred by examining an electrocardiogram. The diagnosis can be confirmed by performing an echocardiogram, in which the now-weakened heart muscle can be visualized.

    Treatment After A Silent Heart Attack

    Once you are found to have had a silent heart attack, two important facts are now known about you. First, you have significant coronary artery disease (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, you should receive all the same treatments as for any other person who has survived a heart attack. Treatment should be aimed at:

    In addition to this standard post-heart attack therapy, people who have had silent heart attacks may need additional treatment based on the results of astress 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(such as taking a nitroglycerin tablet).

    A Word From Verywell

    CAD — 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. People who have had silent heart attacks especially need to pay particular attention to their hearts to prevent further cardiac damage.

    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 further, possibly irreversible, damage to your heart — or worse.

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