Acute Myocardial Infarction

A heart attack is a medical emergency that happens when blood flow to part of the heart muscle suddenly stops, causing damage or death to heart cells. Every year, more than 800,000 people in the United States experience a heart attack, and time is critical—every minute without treatment means more heart tissue is at risk.

What is acute myocardial infarction?
Signs and symptoms
What causes a heart attack?
Risk factors
Types of heart attacks
How is it diagnosed?
Treatment and emergency care
Recovery and rehabilitation
Preventing another heart attack

What is acute myocardial infarction?

Acute myocardial infarction, commonly known as a heart attack, is a serious medical emergency where blood flow to a part of your heart muscle becomes severely reduced or completely blocked^[1]. Without enough blood flow, the affected heart muscle begins to die because it isn’t getting the oxygen it needs^[2].

The medical term myocardial infarction comes from “myocardial,” which refers to the heart muscle, and “infarction,” which means tissue death due to lack of blood supply. When a part of your heart can’t pump because it’s dying from lack of blood flow, it can disrupt the pumping function of your entire heart. This can reduce or stop blood flow to the rest of your body, which can be deadly if not corrected quickly^[2].

The disease affects approximately 3 million people worldwide, with more than 1 million deaths occurring annually in the United States^[1]. In the United States, up to 1.0 million heart attacks occur each year, resulting in death for 300,000 to 400,000 people^[4].

Heart muscle (myocardium)
Coronary arteries
Left ventricle
Right ventricle

Signs and symptoms

Heart attacks can have many symptoms, and recognizing them quickly is crucial because time is critical in treating a heart attack. A delay of even a few minutes can result in permanent heart damage or death^[2].

The most common symptom is chest pain or discomfort. Many people feel pain in their chest during a heart attack. It can feel like discomfort, squeezing, heaviness, pressure, tightness, aching, burning, numbness, fullness, or crushing pain^[2]^[3]. This chest pain typically occurs in the center or left side of the chest and usually lasts for more than a few minutes, or it may go away and come back^[3].

Other common symptoms include pain or discomfort that spreads from your chest to other areas. The pain can radiate to your shoulder, arm (usually the left arm, but it can affect both arms), back, neck, jaw, teeth, or sometimes the upper belly^[2]^[3].

Additional symptoms that people may experience include shortness of breath or trouble breathing, which often comes along with chest discomfort but can also happen before chest discomfort begins^[3]. You might feel weak, lightheaded, dizzy, or feel like you might faint. Many people break into a cold sweat or experience sweating^[2]^[3].

Nausea, vomiting, or a feeling of indigestion are also common symptoms. Some people experience heart palpitations (awareness of heartbeats), anxiety, or a feeling of “impending doom”^[2]. Unexplained tiredness, extreme weakness, or fatigue can also signal a heart attack^[3].

People often think they’re having indigestion or heartburn when they’re actually having a heart attack. Some people only experience shortness of breath, nausea, or sweating without chest pain^[2].

Symptoms can differ between men and women. Women are less likely to have chest pain or discomfort that feels like indigestion. They’re more likely to have shortness of breath, fatigue, and insomnia that started before the heart attack. Women also more commonly have nausea and vomiting or pain in their back, shoulders, neck, arms, or abdomen^[2].

About 30% of people have unusual or atypical symptoms, meaning their symptoms don’t follow the classic pattern^[7]. Some heart attacks may be “silent” and go undetected, occurring without any noticeable symptoms, while others can be catastrophic events leading to sudden death^[5].

If you notice symptoms of a heart attack in yourself or someone else, call emergency services (911 in the United States) immediately. The faster you act, the better the chances of survival and recovery^[6].

What causes a heart attack?

Most heart attacks happen because of a blockage in one of the blood vessels that supply your heart. These blood vessels are called coronary arteries^[2].

The most common cause involves a substance called plaque, which is made up of fat, cholesterol, and other cells. This plaque can build up on the insides of your arteries over time, similar to how pouring grease down your kitchen sink can clog your home plumbing^[2]. This buildup process is called atherosclerosis^[3].

A heart attack typically occurs when one of these plaque deposits inside the coronary arteries breaks open or ruptures. When this happens, a blood clot forms at the site of the rupture^[3]^[6]. The clot can block the supply of blood to the heart, triggering a heart attack. The more time that passes without treatment to restore blood flow, the greater the damage to the heart muscle^[6].

When there’s a large amount of this plaque buildup in the blood vessels to your heart, the condition is called coronary artery disease, which is the main cause of heart attack and the most common cause of death in the United States^[2].

Other less common causes of heart attack include coronary artery embolism (which accounts for 2.9% of patients), cocaine-induced ischemia (lack of blood flow), coronary dissection (a tear in the artery wall), and coronary vasospasm (sudden contraction of the artery)^[1]. A severe spasm or sudden contraction of a coronary artery can also stop blood flow to the heart muscle^[6].

Risk factors

Several health conditions, lifestyle factors, and aspects of your personal history can increase your risk for heart disease and heart attack. These are called risk factors^[5].

About half of all Americans have at least one of three key risk factors for heart disease: high blood pressure, high blood cholesterol, and smoking^[6].

Important modifiable risk factors—those you can change—include smoking or tobacco use, abnormal cholesterol levels, high blood pressure (hypertension), diabetes, obesity or being overweight, lack of physical activity, and an unhealthy diet^[5]^[6].

Additional modifiable risk factors include abdominal obesity (waist-to-hip ratio greater than 0.90 for males and greater than 0.85 for females), psychological factors such as depression, loss of control, stress, financial stress, and major life events like job loss or marital separation^[5]. Lack of daily consumption of fruits or vegetables and alcohol consumption are also factors^[5].

Non-modifiable risk factors—those you cannot change—include your age, family history of heart disease, and sex. Men who are 45 years old or older and women who are 55 years old or older have an increased risk of suffering from a heart attack^[5].

You can take steps to lower your risk by changing the factors you can control. These include quitting smoking if you smoke, losing weight if you’re overweight or obese, doing regular exercise (adults should do at least 150 minutes of moderate-intensity aerobic exercise each week), eating a low-fat, high-fiber diet including whole grains and at least 5 portions of fruit and vegetables a day, and moderating your alcohol consumption^[6].

Types of heart attacks

Heart attacks can be divided into different types based on specific characteristics seen on an electrocardiogram (ECG), a test that records the electrical activity of your heart^[1].

The two main categories are ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation myocardial infarction (NSTEMI)^[1]^[4]. The distinction between NSTEMI and STEMI is vital because treatment strategies are different for these two types^[4].

A condition called unstable angina resembles an NSTEMI, but it is distinguished by normal cardiac markers (substances in the blood that indicate heart damage)^[1].

Heart attacks can also be classified into 5 types based on their cause and circumstances. Type 1 is a spontaneous heart attack caused by a primary coronary event such as plaque rupture or coronary dissection. Type 2 occurs due to increased oxygen demand (such as from high blood pressure) or decreased oxygen supply (such as from coronary artery spasm, embolism, arrhythmia, or low blood pressure). Type 3 is related to sudden unexpected cardiac death. Type 4a is associated with percutaneous coronary intervention (a procedure to open blocked arteries), and Type 4b is associated with stent thrombosis. Type 5 is associated with coronary artery bypass grafting surgery^[4].

Heart attacks predominantly affect the left ventricle (the main pumping chamber of the heart), but damage may extend into the right ventricle or the upper chambers of the heart^[4].

The location of the heart attack also varies. Anterior infarcts (affecting the front of the heart) tend to be larger and result in a worse prognosis than inferoposterior infarcts (affecting the bottom and back of the heart)^[4].

The extent of tissue damage can be described as transmural (affecting the full thickness of the heart wall) or nontransmural (affecting only part of the wall thickness)^[4].

How is it diagnosed?

The first goal for healthcare professionals in managing a heart attack is to diagnose the condition very rapidly. Early diagnosis is crucial because early treatment within 6 hours of symptom onset significantly improves prognosis^[1].

A heart attack is diagnosed when 2 of the following criteria are met: symptoms of ischemia (reduced blood flow); new ST-segment changes or a left bundle branch block on electrocardiogram; presence of pathological Q waves on ECG; new regional wall motion abnormality on imaging studies; or presence of a blood clot in the coronary artery found at autopsy or during an angiogram^[1].

If you’re able to answer questions when you arrive at the hospital, you may be asked about your symptoms and medical history. Healthcare providers will check your blood pressure, pulse, and temperature^[3].

The primary diagnostic tests include an electrocardiogram (ECG or EKG), which is typically the first test done. This test records electrical signals as they travel through the heart. Sticky patches called electrodes are attached to the chest and sometimes the arms and legs. The signals are recorded as waves displayed on a monitor or printed on paper. An ECG can show if you are having or have had a heart attack^[3].

Blood tests are crucial for diagnosis. Certain heart proteins slowly leak into the blood after heart damage from a heart attack. These are called cardiac biomarkers or cardiac markers, and the preferred marker is cardiac troponin^[3]^[4]. A rise of cardiac biomarkers above a specific threshold, combined with other findings, confirms the diagnosis^[4].

Additional diagnostic tests may include a chest X-ray to show the condition and size of the heart and lungs^[3]. An echocardiogram uses sound waves (ultrasound) to create images of the moving heart, showing how blood moves through the heart and heart valves. This test can help identify whether an area of your heart has been damaged^[3].

Coronary catheterization, also called an angiogram, involves inserting a long, thin tube (catheter) into an artery, usually in the leg, and guiding it to the heart. Dye flows through the catheter to help the arteries show up more clearly on images made during the test. This procedure can show how well blood is moving through your heart^[3].

Advanced imaging tests such as cardiac CT (computed tomography) or cardiac MRI (magnetic resonance imaging) can create detailed images of the heart and chest^[3].

Treatment and emergency care

A heart attack is a life-threatening emergency. If you think you or someone you’re with is having a heart attack, call emergency services immediately. The sooner you get to an emergency room, the sooner you can get treatment to reduce the amount of damage to the heart muscle^[1].

While waiting for an ambulance, it may help to chew and then swallow a tablet of aspirin (ideally 300mg), as long as the person having a heart attack is not allergic to aspirin. Aspirin helps to thin the blood and improves blood flow to the heart^[6].

At the hospital, healthcare professionals can run tests to find out if a heart attack is happening and can decide the best treatment. In some cases, a heart attack requires cardiopulmonary resuscitation (CPR) or an electrical shock (defibrillation) to the heart to get the heart pumping again^[6].

Initial therapy for acute heart attack is directed toward restoration of blood flow as soon as possible to salvage as much of the threatened heart muscle as possible. This may be accomplished through medical treatments or mechanical procedures^[11].

Treatment typically includes several types of medications. Antiplatelets (such as aspirin), anticoagulants (blood thinners), nitrates, beta-blockers, and statins are commonly used^[4]. Early initiation of oral beta blocker therapy (within 24 hours) is recommended in those with acute coronary syndrome who don’t have contraindications, to lower the risk of another heart attack and dangerous heart rhythms^[11].

For ST-segment elevation myocardial infarction (STEMI), emergency restoration of blood flow is crucial. This can be done using fibrinolytic drugs (medications that dissolve blood clots), percutaneous coronary intervention (a procedure where doctors use a catheter to open blocked arteries, often placing a small metal mesh tube called a stent to help keep the artery open), or occasionally, coronary artery bypass graft surgery^[4].

For non-ST-segment elevation myocardial infarction (NSTEMI), blood flow restoration is typically achieved through percutaneous coronary intervention or coronary artery bypass graft surgery^[4].

If doctors find that blood moves slowly or not at all through your coronary arteries, you have either a narrowed or blocked artery. Doctors can perform an emergency procedure called angioplasty to open narrowed or blocked blood vessels^[9].

Recovery and rehabilitation

Recovering from a heart attack can take several months, and it’s very important not to rush your rehabilitation. The time it takes to recover will depend on the amount of damage to your heart muscle^[6].

Typically, you’ll be in the hospital for 2 days to a week after a heart attack. If you have complications or have had other procedures like bypass surgery, you’ll probably stay longer^[24].

During your recovery period, you’ll receive help and support from a range of healthcare professionals, which may include nurses, physiotherapists, dietitians, pharmacists, and exercise specialists^[6].

The two most important aims of the recovery process are to gradually restore your physical fitness so you can resume normal activities (known as cardiac rehabilitation) and to reduce your risk of another heart attack^[6].

Cardiac rehabilitation is a program to help you recover and get back to living your life after a heart attack. It’s an important part of your recovery. Research has found that people who attend cardiac rehab have a lower risk of having another heart attack and being admitted to hospital. It also has a positive impact on their wellbeing and quality of life^[6].

Most cardiac rehab programs consist of three parts: exercise led by a certified exercise specialist; classes on how to lower your risk of further problems; and support for dealing with stress, anxiety, and depression^[24]. Your cardiac rehab team will tailor the program to suit your age, fitness level, and any other medical issues^[6].

Once you return home, it’s usually recommended that you rest and only do light activities, such as walking up and down the stairs a few times a day or taking a short walk. Gradually increase the amount of activity you do each day over several weeks. How quickly you can do this will depend on the condition of your heart and your general health^[6].

Most people can return to work after having a heart attack, but how quickly will depend on your health, the state of your heart, and the kind of work you do^[6].

After a heart attack, it’s normal to experience emotional responses including fear, depression, denial, and anxiety. These often last anywhere from 2 to 6 months and can affect your ability to exercise, family life and work, and overall recovery. Some time with your doctor or a mental health specialist can help you deal with negative feelings^[24].

Preventing another heart attack

After you have a heart attack, your chance of having another one is higher. There are important steps you can take to prevent another heart attack^[6].

If you smoke, the single most important thing you can do—not just for your heart but for your entire body—is to stop. It’s also one of the hardest changes to make, but your doctor can help with a plan for quitting, alternatives to tobacco such as nicotine gum or patches, prescription medications, and support groups^[24]. It’s also important to insist that people not smoke in your home and to stay away from places where smokers gather, as secondhand smoke can raise your chance of having heart disease^[24].

You’ll need to treat high blood pressure and high cholesterol, as both of these damage your arteries and increase your risk of heart attack and stroke over time. Exercise, a healthy diet, and lifestyle changes can help, but you may also need to take medications^[24].

If you have diabetes, managing it properly is essential to reduce your cardiovascular risk^[24].

Regular exercise is crucial for recovery and prevention. Adults should do at least 150 minutes (2 hours and 30 minutes) of moderate-intensity aerobic exercise each week, unless advised otherwise by your doctor^[6].

Following a healthy diet is important. Eat a low-fat, high-fiber diet, including whole grains and at least 5 portions of fruit and vegetables a day^[6].

If you’re overweight or obese, losing weight will help reduce your risk^[6].

Moderate your alcohol consumption. While the relationship is complex, excessive alcohol use should be avoided^[6].

One of the first things you may notice in the hospital is that your medication routine might change. The doctor might make adjustments to your dosage or the number of medicines you take, and you’ll probably be put on new medications. These will treat and control your symptoms and the factors that led to your heart attack. You may need to take these medicines for the rest of your life^[24].

Make sure you know the names of everything you take, are clear on how and when to take them, understand what each medicine does and why you’re taking it, and ask your doctor about side effects^[24].

How well you do after a heart attack depends on the damage to your heart, where the damage is, and what steps you take to prevent another one^[6].