Causes and Risk Factors of a Heart Attack

A heart attack (myocardial infarction, or MI) occurs when a portion of the heart muscle has died—most often when 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). There are other conditions that can lead to myocardial infarction as well. 

When a coronary artery plaque—a build-up of lipids and other substances in the artery—ruptures, it immediately causes the formation of a blood clot (localized thrombosis) that impede blood flow to the heart. This must be considered alongside other potential causes of heart attack.

The disruption of a plaque followed by blood clot formation is called acute coronary syndrome, or ACS. The consequences of ACS depend on the extent to which the artery is blocked by the new blood clot. Acute coronary syndrome associated with typical CAD is, by far, the most common cause of myocardial infarction.

When a blood clot dissolves so quickly there's no damage to the heart, the episode is referred to as unstable angina. Often, though, the blockage is severe enough to cause the death of a portion of heart muscle being supplied by the damaged artery, leading to a heart attack.

Also known as Prinzmetal angina, vasospastic angina, or variant angina, coronary artery spasm is exactly what it sounds like: a sudden involuntary contraction of a coronary artery.

Most people with coronary artery spasm will have episodes of angina, most often experienced as chest pressure or pain, rather than an actual myocardial infarction. However, a severe and prolonged episode of coronary artery spasm can result in permanent damage to a portion of the heart muscle.

Very rarely, a condition called microvascular angina (or cardiac syndrome X) will lead to a heart attack. Microvascular angina is caused by endothelial dysfunction, in which the smaller coronary arteries fail to dilate normally, creating an obstruction to blood flow.

People with microvascular angina will have normal-looking coronary arteries during cardiac catheterization, a test used to evaluate and treat heart conditions.

Nicknamed "broken heart syndrome," stress cardiomyopathy is sudden, severe heart failure triggered by extreme emotional trauma or physical stress.

With aggressive treatment, most people who have this condition 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 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.

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

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.

Certain medical conditions increase the risk of blood clot embolization, including atrial fibrillation, dilated cardiomyopathy, as can the presence of an artificial heart valve. In these cases, blood thinners can help prevent this from happening.

Scientists don't fully understand the ways in which the risk of myocardial infarction might, in some people, be related to an underlying genetic predisposition.

For example, it's known that, in some families, the elevated risk clearly is related to an identifiable inherited disorder such as familial hypercholesterolemia.

At the same time, although researchers have been able to identify certain gene variants associated with diseases that ultimately lead to heart failure, such as like hypertrophic cardiomyopathy, they have not been able to pin down who with this gene variant is most likely to develop this condition.

What's more, genetic factors that may be involved in a person's risk of heart attack may not be directly linked to a particular cardiovascular condition, but rather to an elevated risk of a trait associated with an increased heart disease risk, such as a tendency to be overweight, have abnormal blood lipid levels, or to develop type 2 diabetes or hypertension.

Aside from genetics, there are a handful of other uncontrollable factors that can increase the possibility a person could have a heart attack:

• Age: The risk increases for men who are 55 or older and women who are 65 and older.
• Chronic kidney disease
• Type 1 diabetes
• For women, being post-menopausal or have had an ovary removal

The silver lining for someone whose parents have passed down a genetic tendency to, say, easily become overweight or develop high blood pressure is that these risks can often be managed with healthy lifestyle strategies.

At the same time, a variety of lifestyle factors can put anyone, regardless of family history, at increased risk of a heart attack. The most important ones include:

• Obesity, especially if most excess weight is located in the abdominal area
• Inactivity: People who engage in regular exercise have a decreased risk of heart problems.
• High blood levels of low-density lipoprotein (LDL) cholesterol or triglycerides (fats)
• Low levels of high-density lipoprotein (HDL) cholesterol
• Hypertension (high blood pressure)
• Type 2 diabetes and insulin resistance
• Smoking and other types of tobacco use: In fact, smoking is the chief cause of heart attacks in people under 40.

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. More important to know: There are many things you can do to prevent this from happening, from eating a healthy diet to getting regular exercise to not smoking (or kicking the habit if you already do). These measures may help mitigate your risk even if heart problems run in your family, and they'll help prevent you from developing other chronic conditions as well.