Causes of Myocardial Infarction (Heart Attack)

Senior with Chest Pain
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Causes of Myocardial Infarction (Heart Attack)

A myocardial infarction, or heart attack, means that some portion of the heart muscle has died. Heart attacks almost always happen when the blood supply to the heart muscle has been cut off. In most cases, a heart attack is an acute event, resulting from the sudden rupture of an atherosclerotic plaque in the wall of a coronary artery, in a person with typical coronary artery disease (CAD). However, there are other conditions that can also produce a myocardial infarction. 

Causes of Myocardial Infarction

Acute Coronary Syndrome 

In the vast majority of cases, heart attacks are caused by a rupture or erosion of a coronary artery plaque, which immediately leads to localized thrombosis (blood clot formation) in the artery. The disruption of a plaque with subsequent blood clot formation is referred to as acute coronary syndrome, or ACS.

The consequences of ACS depend on the extent to which the artery is blocked by the new blood clot. In many cases, the clot will dissolve rather quickly, and the patient will experience “only” an episode of unstable angina. All too often, however, the blockage is severe enough to cause the death of at least some of the heart muscle being supplied by the damaged artery. In other words, a heart attack occurs. If only some of the heart muscle dies, the patient will have a non-ST segment myocardial infarction (NSTEMI). If nearly all of the muscle supplied by the occluded artery dies, an ST-segment elevation myocardial infarction (STEMI) occurs.

Acute coronary syndrome associated with typical CAD is, by far, the most common cause of myocardial infarction.

Coronary Artery Spasm

Coronary artery spasm (often called Prinzmetal angina), is a condition which produces spasm in a coronary artery. Most people with coronary artery spasm will experience episodes of angina rather than an actual myocardial infarction. However, a severe and prolonged episode of coronary artery spasm can indeed result in permanent damage to a portion of the heart muscle.

Microvascular Angina

Microvascular angina, or cardiac syndrome x, is a condition in which angina (and more rarely, a heart attack) is caused by an abnormal functioning of the small coronary arteries, specifically, by endothelial dysfunction. In this condition, the smaller arteries fail to dilate normally, creating a relative obstruction to blood flow. People with microvascular angina will have normal-looking coronary arteries during cardiac catheterization, and no coronary artery spasm will be provokable during the test. While chest pain is common in people with microvascular angina (and can be difficult to treat), an actual heart attack is a relatively unlikely event.

Stress Cardiomyopathy

Stress cardiomyopathy (often called “broken heart syndrome”), is a dramatic heart condition, typically triggered by an episode of sudden stress or shock, that causes sudden, severe, heart failure. With aggressive treatment, most people who have this condition can survive with normally-functioning hearts. But in some cases, at least some part of the heart muscle is permanently damaged. The cause of this condition is unknown, but it is thought to be related to endothelial dysfunction, similar to microvascular angina.

Viral Myocarditis

Viral myocarditis is a viral infection directly affecting the heart muscle. Most doctors do not think of viral myocarditis as a cause of myocardial infarction, though it often does cause permanent heart muscle damage. It seems to do this by producing extensive localized inflammation in cardiac muscle, with the interruption of the local blood supply.

Blood Clotting Disorders

Certain disorders of the blood clotting mechanism, such as Factor V Leiden, predispose to abnormal blood clotting. People with such conditions can develop acute thrombosis of a coronary artery even without any underlying CAD, and thus, can experience myocardial infarctions.

Coronary Artery Embolism

A myocardial infarction can occur if a blood clot, usually originating within the heart, breaks free and becomes lodged in a coronary artery, interrupting the blood supply to part of the heart muscle. Several conditions predispose to blood clot embolization, including atrial fibrillationdilated cardiomyopathy, and the presence of an artificial heart valve. People with conditions known to cause blood clots in the heart are usually treated with blood thinners to prevent this from happening.

Genetics and Myocardial Infarction

There is little question that the risk of atherosclerosis, and thus the risk of heart attacks, is related to genetic predisposition. That is, the risk of premature heart attacks tends to run in families. In some families, the elevated risk is clearly related to some identifiable inherited disorder, such as familial hypercholesterolemia, or Factor V Leiden.

In most cases, however, the genetic propensity for myocardial infarction is multifactorial, and cannot be attributed to a specific, well-defined inherited condition. For instance, some people are genetically more prone to become overweight, to have abnormal blood lipid levels, or to develop type 2 diabetes, or hypertension — all of which are strong risk factors for heart disease.

Risk Factors For Myocardial Infarction

Several important risk factors have been identified that greatly increase a person’s odds of having a heart attack. These risk factors include being overweight, being relatively sedentary, high LDL cholesterol or triglycerides, low HDL cholesterol, smoking, hypertension, diabetes, and insulin resistance. All of these risk factors can be improved either with medication or with lifestyle changes. 

A Word From Verywell

Most heart attacks are caused by a rupture of an atherosclerotic plaque in a coronary artery, but there are several other, much less common, causes as well. By working with our doctors to assess our risk, and taking reasonable steps to maintain our health, there is very likely al lot we can do to reduce our risk of having a heart attack. 

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Article Sources
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