Causes and Risk Factors of a Heart Attack

A heart attack (myocardial infarction, or MI) occurs when a portion of the heart muscle is deprived of blood and becomes damaged. In most cases, a heart attack is a sudden event that occurs when an atherosclerotic plaque—a build-up of lipids and other substances in the artery—in the wall of a coronary artery ruptures (breaks off) and causes a blood clot to form, blocking a smaller artery in the heart muscle. This often occurs due to longstanding coronary artery disease (CAD). There are other conditions that can lead to myocardial infarction as well. 

Common Causes

A heart attack is necrosis (death) of the heart muscle. This occurs due to insufficient blood supply. A thrombus (localized blood clot) due to a ruptured coronary artery plaque is the most common reason for heart muscle necrosis, and there are several other causes as well.

A heart attack usually causes angina, which feels like chest pressure, tightness, or pain. It usually also causes severe shortness of breath.

Acute Coronary Syndrome 

When a coronary artery plaque ruptures, it can cause the formation of a blood clot (localized thrombosis) that impedes blood flow to the heart.

This 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 quickly, before the heart becomes damaged, the episode is referred to as unstable angina. If the blockage is severe enough to cause death of a portion of the heart muscle—this is a heart attack.

Coronary Artery Spasm

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 brief episodes of angina, rather than an actual myocardial infarction. A severe and prolonged episode of coronary artery spasm can result in permanent damage to a portion of the heart muscle.

Microvascular Angina

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 don't dilate (widen) 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.

Stress Cardiomyopathy

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

With appropriate treatment, most people who have this condition survive and have recovery of heart function. But in some cases, part of the heart muscle can be 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 that directly affects the heart muscle. Viral myocarditis is not typically considered a cause of myocardial infarction, though it often does cause permanent heart muscle damage. It is believed to produce extensive localized inflammation in the cardiac muscle and interruption of the local blood supply.

Blood Clotting Disorders

Certain disorders of the blood-clotting pathway, such as Factor V Leiden deficiency, predispose 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.

Coronary Artery Embolism

A myocardial infarction can occur if a blood clot, usually originating within the heart, embolizes (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, and the presence of an artificial heart valve. In these cases, blood thinners are often prescribed to help prevent this from happening.

Genetics

Genetic factors that may be involved in a person's risk of heart attack can be directly linked to a particular cardiovascular condition or 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 develop type 2 diabetes or hypertension.

While some specific genes and hereditary patterns have been identified, there are many unknowns when it comes to genetic risk factors for heart attack.

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

However, although researchers have been able to identify certain gene variants associated with diseases that ultimately lead to heart failure, such as hypertrophic cardiomyopathy, having the gene variant does not necessarily mean that you will develop this condition.

Non-Controllable Risk Factors

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 having had an ovary removal

Lifestyle Risk Factors

Whether you have a genetic predisposition to heart attacks or not, your risks can often be reduced with healthy lifestyle strategies.

Keep in mind that lifestyle factors can put anyone, regardless of family history, at an 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

A Word From Verywell

Most heart attacks are caused by the dislodging 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—eating a healthy diet, getting regular exercise, and 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.