Heart attack

A heart attack occurs when blood flow to an artery supplying a section of heart muscle becomes blocked. If the flow of blood is not restored quickly, the section of heart muscle becomes damaged from lack of oxygen and begins to die. This often causes pain, shortness of breath, heart rhythm problems, or even sudden death.

Other heart conditions associated with a heart attack can include heart failure and arrhythmias (irregular heartbeats). Heart failure is a condition in which the heart cannot pump enough blood to the body. There are many types of arrhythmias, some of which are life-threatening. An example is ventricular fibrillation, which is fatal if not treated immediately.

Heart attack is a leading cause of death in both men and women in the United States, and is on the rise around the world.

Other Terms

Other terms for heart attack include:

• Myocardial infarction or MI
• Acute myocardial infarction or AMI
• Acute coronary syndrome
• Coronary thrombosis
• Coronary occlusion

Types

Heart attacks are classified by physicians in several ways.

• By the region of the heart that was affected: For example, physicians may speak of a patient having an anterior, a posterior, or a right-sided MI.
• By how the heart attack looked on an electrocardiogram (EKG): For example, an ST-elevation MI refers to an abnormal tracing that shows up on EKG, while a non-ST elevation MI may be detected with blood tests only.
• By how severe the heart attack was: The Killip classification is a way of predicting whether the patient is likely to die within 30 days, and measures how much congestive heart failure has accompanied the heart attack.^[1]

Symptoms

Not all heart attacks begin with a sudden, crushing pain, and the warning signs and symptoms of a heart attack are not the same for everyone. Many heart attacks start slowly as mild pain or discomfort while some people do not have symptoms at all (a silent heart attack).

Discomfort or pain

The most common symptom of heart attack is chest discomfort or pain. Most heart attacks involve discomfort in the center of the chest that lasts for more than a few minutes or goes away and comes back. The discomfort can feel like uncomfortable pressure, squeezing, fullness, or pain. It can be mild or severe. This discomfort or pain lasts more than a few minutes, or it goes away and comes back. Heart attack pain can sometimes feel like indigestion or heartburn. Symptoms for one heart attack may not be like a patient's previous one(s). The patient may say the chest pain radiates to the upper body in one or both arms, the back, neck, jaw, or stomach.

The symptoms of angina can be similar to the symptoms of a heart attack. Angina is pain in the chest that occurs in people with coronary artery disease, usually occurring at times during activity. Anginal pain usually lasts for only a few minutes and goes away with rest. Angina that does not go away, or angina that changes from its usual pattern (occurring more frequently or occurring at rest) can be a sign of the beginning of a heart attack. This is termed unstable angina.

Other signs and symptoms

Other common signs and symptoms that a person can have during a heart attack include:

• Upper body discomfort in one or both arms, the back, neck, jaw, or stomach
• Shortness of breath with or before chest discomfort
• Nausea, vomiting, lightheadedness or fainting, or breaking into a cold sweat

Atypical signs and symptoms

Unfortunately, many heart attacks do not follow the textbook pattern. Particularly in elderly people and diabetics, symptoms can be subtle or even silent, and women's symptoms are frequently different from the commonly-studied group above. In people who have risk factors for heart attacks, even subtle symptoms are suspicious. As an example, an elderly diabetic woman may suffer a heart attack and merely feel a little sick.

Causes

Heart attacks occur most often as a result of a condition called coronary artery disease (CAD). In CAD, a deposition of material called plaque builds up over many years on the inside walls of the coronary arteries (the arteries that supply blood and oxygen to the heart). Eventually, an area of plaque can break open, which causes a blood clot to form on the surface of the plaque. If the clot becomes large enough, it can severely or completely block the flow of oxygen-rich blood to the part of the heart muscle fed by the artery. If oxygen is not restored to dying muscle, and if the person survives the heart attack, that portion of muscle is replaced by scar tissue. This heart damage may not cause symptoms, or it may cause severe or long-lasting problems.

A normal artery with normal blood flow and an artery containing plaque buildup. Source: NHLBI.

Figure A shows an overview of the heart and coronary artery. Figure B shows a cross-section of the coronary artery with plaque buildup and a blood clot. Source: NHLBI.

Heart attack also can occur due to problems with the tiny, microscopic blood vessels of the heart. This condition is called microvascular disease. It is believed to be more common in women than in men.

Another less common cause of heart attack is a severe spasm (tightening) of a coronary artery that cuts off blood flow through the artery. These spasms can occur in coronary arteries that do not have CAD. It is not always clear what causes a coronary artery spasm, but sometimes it can be related to:

• Certain drugs—cocaine is a common culprit
• Emotional stress or pain
• Exposure to extreme cold
• Cigarette smoking

Diagnosis

Not all heart attacks are obvious, and diagnosis should be based on each patient's situation: his symptoms and his personal risk factors. Age, family history, other medical problems (especially diabetes), previous heart attacks, use of drugs like cocaine, history of smoking, and cholesterol levels are among the important risk factors. Chest pain and other symptoms of heart attack can also occur in other diseases, like aortic dissection and pneumonia, so diagnosing heart attacks is not always straightforward. Emergency physicians miss the diagnosis in about 2%–5% of patients in the U.S.^[2] and Canada,^[3] respectively, and in up to 6% of patients in the United Kingdom.^[4]

Electocardiogram (EKG)

An electrocardiogram detects and records the electrical activity of the heart with painless stickers on the chest. Certain changes in the appearance of the electrical waves on an EKG are strong evidence of a heart attack. An EKG also can show arrhythmias (abnormal heartbeats), which a heart attack and other conditions can cause. An EKG can sometimes give an immediate diagnosis of a heart attack. At other times it may suggest heart damage or abnormalities that are not conclusive. Occasionally, heart attacks occur in the context of normal or near-normal EKGs, so it is not a perfect test.^[5] The EKG changes with time during a heart attack, so a physician assessing someone with a possible heart attack may repeat it several times.

If a heart attack is confirmed, the EKG findings become important. An EKG may shows signs that the heart muscle is badly damaged, which is determined by an area of the EKG tracing called the "ST segment". If the ST segment is elevated, then muscle damage is severe and treatment is more aggressive. This is termed an ST segment myocardial infarction, or STEMI. There is a milder form of heart attack called a non-STEMI or NSTEMI, which, although less severe can still cause heart dysfunction, arrhythmias and death.

Cardiac biomarkers

Cardiac biomarkers are proteins released into the bloodstream by damaged heart muscle, after cells die and release their contents. Cardiac biomarkers are often referred to as "cardiac enzymes," although this is not an accurate term since not all cardiac biomarkers are enzymes. A blood test can detect these biomarkers and determine if they are abnormally elevated. There are several biomarkers that are released by damaged heart muscle cells, and each has a typical timing of maximal release after a heart attack. Thus when a heart attack is suspected, doctors perform a sequence of blood tests for biomarkers at timed intervals to look for abnormal elevations that would indicate heart muscle damage. The most commonly measured biomarkers include muscle enzymes such as[Creatine Kinase|creatine kinase]] or creatine phosphokinase (CK or CPK), CK-MB (a form of CK found only in heart muscle), and troponin, either troponin I or troponin T. Troponin is not an enzyme, but rather is one of the contractile protein elements of the myocardial cell. Myoglobin was commonly measured in the past but is considered less helpful nowadays. If a rise in biomarkers to an abnormal degree is noted, a heart attack (myocardial infarction) is often diagnosed. Sometimes excessive strain on the heart can cause a slight rise in these enzymes, and they can also be elevated in patients with kidney failure. These latter two situations are not myocardial infarctions but rather elevations in biomarker levels by a different mechanism.

Coronary angiography

Coronary angiography is a special x-ray exam of the heart and blood vessels. It is often done during a heart attack to help pinpoint the exact location of the blockages in the coronary arteries.

The doctor passes a catheter (a thin, flexible tube) through an artery in the patient's arm or groin (upper thigh) and threads it to the heart. This procedure, called cardiac catheterization, is part of coronary angiography.

A dye that can be seen on x-ray is injected into the bloodstream through the tip of the catheter. The dye lets the doctor study the flow of blood through the heart and blood vessels.

If a blockage is found, another procedure, called angioplasty, may be used to restore blood flow through the artery. This involves passing an uninflated balloon through an area of blockage and then inflating it until the blockage is flattened and the vessel has re-opened. Sometimes during angioplasty, the doctor will place a stent (a small mesh tube) in the artery to help keep the artery open. This is described in more detail below.

Treatment

Early treatment can prevent or limit damage to the heart muscle. Medical personnel can begin diagnosis and treatment even before a patient arrives to the hospital.

Certain treatments are usually started right away if a heart attack is suspected, even before the diagnosis is confirmed. These include:

• Oxygen
• Aspirin to prevent further blood clotting (unless the patient is allergic)
• Nitroglycerin to reduce the workload on the heart and improve blood flow through the coronary arteries
• Treatment for chest pain with morphine

Once the diagnosis of heart attack is confirmed or strongly suspected, treatments to try to restore blood flow to the heart are started as soon as possible. Treatments include medications and medical procedures.

Medicines

A number of different kinds of medicines may be used to treat heart attack. They include the following:

Thrombolytic medicines

Thrombolytic medicines (also called clot busters) are used to dissolve blood clots that are blocking the coronary arteries. To be most effective, these medicines must be given within 1 hour after the start of heart attack symptoms.

Examples of thrombolytics include tPA (Alteplase), streptokinase, anistreplase, and reteplase.

Because their most severe complication is bleeding in the brain (hemorrhagic stroke) thrombolytics are not safe under certain circumstances. They are to be avoided in people with a history of hemorrhagic stroke; pregnant women; bleeding from the gastrointestinal tract; history of surgery on the brain or spine; recent trauma; and in several other situations.

Beta blockers

Beta blockers decrease the workload of the heart. Beta blockers are used to decrease the heart rate and prevent further heart attacks. Beta blockers also are used to prevent or correct certain arrhythmias (irregular heartbeats), which can occur as a result of a heart attack and can be fatal. A beta blocker commonly used during heart attacks is metoprolol.

Angiotensin-converting enzyme (ACE) inhibitors

ACE inhibitors are being given increasingly commonly to patients within the first day or so of a heart attack.^[6] These medicines lower blood pressure and reduce the strain on the heart. They also help slow down further weakening of the heart muscle. An example is lisinopril.

Anticoagulants

Anticoagulant medicines thin the blood and prevent clots from forming in the arteries. An example is heparin.

Antiplatelet medicines

Antiplatelet medicines (such as aspirin and clopidogrel) stop platelets (a type of blood cell) from clumping together and forming unwanted clots.

Other medicines

Medicines may also be given to relieve pain and anxiety, and to treat arrhythmias, which often occur during a heart attack. A cholesterol-lowering drug may also be given in the hours and days following heart attack (such as simvastatin and atorvastatin). These drugs prevent heart attacks in the long run and may help in recovery of the heart immediately after the heart attack.^[7]

Medical procedures

If medicines cannot stop a heart attack, medical procedures, surgical or nonsurgical, may be used. These procedures include the following:

Angioplasty

Angioplasty is a nonsurgical procedure that can be used to open coronary arteries that are blocked by a blood clot. During angioplasty, a catheter (a thin, flexible tube) with a balloon on the end is threaded through a blood vessel to the blocked coronary artery. Then, the balloon is inflated to push the plaque against the wall of the artery. This widens the inside of the artery, restoring blood flow.

During angioplasty, a small mesh tube called a stent may be put in the artery to help keep it open. Some stents are coated with medicines that help prevent the artery from becoming blocked again.

Angioplasty and angiography are done together; they are sometimes referred to as percutaneous intervention (PCI). If a heart attack is confirmed and the EKG indicates death of the heart muscle (so called ST-segment elevation MI, or STEMI), doctors will aim to perform this procedure within 90 minutes of a patient arriving in the hospital. This is because the amount of heart dysfunction after the heart attack is much lower in those whose blood supply to the heart is restored the quickest.

Coronary artery bypass grafting

Coronary artery bypass grafting (CABG) is a surgery in which arteries or veins are taken from other areas of the body and sewn in place to bypass (that is, go around) blocked coronary arteries. This provides a new route for blood flow to the heart muscle.

CABG is considered a better choice than stenting for people with coronary artery disease in multiple arteries of their heart, while people with disease in just one vessel generally should get stents.^[8]

Cardiac rehabilitation

Most people spend several days in the hospital after a heart attack. After hospitalization, treatment does not stop. At home, treatment may include daily medicines and cardiac rehabilitation (rehab). The doctor may recommend lifestyle changes, including smoking cessation, losing weight, altering diet, and increasing physical activity, to lower the chances of having another heart attack.

Cardiac rehabilitation is prescribed after a heart attack, and includes exercise, education, counseling, and learning about reducing risk factors. Almost everyone who has had a heart attack can benefit from rehab. The heart is a muscle, and the right exercise will strengthen it.

The cardiac rehab team may include doctors (a family doctor, a cardiologist, and/or a surgeon), nurses, exercise specialists, physical and occupational therapists, dietitians, and psychologists or other behavioral therapists.

Prevention

Lowering risk factors for coronary artery disease (CAD) can help prevent a heart attack. Even people who already have CAD can still take steps to lower their risk of heart attack.

Reducing the risk of heart attack usually means making healthy choices and seeking treatment for medical conditions that raise risk.

Healthy choices

Healthy choices to help prevent heart attack include:

• Eating a low-fat diet rich in fruits and vegetables. Paying careful attention to the amounts and types of fat in the diet, particularly saturated fats. Lowering the salt intake. Avoiding simple carbohydrates in favor of whole grains. These changes can help lower high blood pressure and improve blood cholesterol.
• Losing weight if obese.
• Quitting smoking.
• Doing physical activity to improve heart fitness.

Treating related conditions

In addition to making lifestyle changes, people can help prevent heart attacks by treating the following conditions that make a heart attack more likely, such as high "bad" cholesterol, low "good" cholesterol (HDL), high blood pressure, and diabetes (high blood sugar).

Chances of Having a Heart Attack

Certain risk factors make it more likely that a person will develop coronary artery disease (CAD) and have a heart attack. Some risk factors for heart attack can be controlled, while others cannot.

Major controllable risk factors for heart attack include:

• Smoking
• High blood pressure
• High blood cholesterol
• Obesity
• Physical inactivity
• Diabetes (high blood sugar).

Uncontrollable risk factors include:

• Age: The risk increases for men older than 45 years and for women older than 55 years (or after menopause).
• Family history of early CAD: Risk increases if a father or a brother was diagnosed with CAD before 55 years of age, or if a mother or a sister was diagnosed with CAD before 65 years of age.

Certain CAD risk factors tend to occur together. When they do, it is called metabolic syndrome. In general, a person with metabolic syndrome is much more likely to develop heart disease and diabetes than is someone without metabolic syndrome.

Related Problems

Anxiety and depression

After a heart attack, many people worry about having another heart attack. Sometimes they feel depressed and have trouble adjusting to the new lifestyle that is needed to limit further heart trouble. Medicine and professional counseling are often recommended for depression or anxiety. Physical activity, with physician guidance, can improve mental well-being.

Risk of a repeat heart attack

After one heart attack, the risk of having another one goes up. It is important to know the difference between angina and a heart attack. The pain of angina usually occurs after exertion and goes away in a few minutes with rest or nitroglycerin. During a heart attack, the pain is usually more severe than angina, and it does not go away with rest or medicine.

Unfortunately, most heart attack victims wait 2 hours or more after their symptoms begin before they seek medical help. This delay can result in lasting heart damage or death.

Expected Outcome

Many people survive heart attacks and live active and full lives. Getting help quickly can limit the damage to heart muscle. Less heart damage improves the chances for a better quality of life after a heart attack.

Medical follow-up

After a heart attack, patients will need treatment for coronary artery disease to prevent another heart attack. The doctor may recommend:

• Lifestyle changes, such as quitting smoking, following a healthy diet, increasing physical activity, and losing weight, if needed
• Medicines to control chest pain or discomfort, blood pressure, blood cholesterol, and the heart’s workload
• Participation in a cardiac rehabilitation program

Returning to normal activities

After a heart attack, most people without chest pain or discomfort or other complications can safely return to most of their normal activities within a few weeks. Most can begin walking immediately. Sexual activity also can begin within a few weeks for most patients.

If allowed by state law, driving can usually begin within a week for most patients who do not have chest pain or discomfort or other complications. Each state has rules about driving a motor vehicle following a serious illness.

Epidemiology

According to the American Heart Association, coronary heart disease, which includes heart attack and angina, caused 451,326 deaths in the United States in 2004 (one of every five deaths). From 1994 to 2004, the death rate from coronary heart disease declined 33 percent, but the actual number of deaths declined only 18 percent.

Incidence

Incidence is the number of new events in a given year. According to the American Heart Association, there are approximately 1,200,000 new and recurrent coronary attacks per year, and about 38 percent of people who experience a coronary attack in a given year die from it. According to the World Health Organization, 7.2 million people worldwide die from heart attacks each year, and at least 20 million more survive heart attacks.^[9]

Prevalence

Prevalence is the number of events in a population at a designated time. In this case, it includes events in a patient's past. According to the American Heart Association, there are 16,000,000 victims of angina (chest pain due to coronary heart disease), heart attack, and other forms of coronary heart disease who are still living (8,700,000 males and 7,300,000 females).

Among adults in the United States age 20 and older, the estimated age-adjusted prevalence of coronary heart disease for non-Hispanic whites is 9.4 percent for men and 6.0 percent for women; for non-Hispanic blacks, 7.1 percent for men and 7.8 percent for women; and for Mexican-Americans, 5.6 percent for men and 5.3 percent for women.

Clinical Trials

Click here for a list of clinical trials studying heart attack.

References

1. ↑ Clinical Trials Networks Best Practices: Killip Classification.
2. ↑ Pope JH, Aufderheide TP, Ruthazer R. Missed diagnoses of acute cardiac ischemia in the emergency department. N Engl J Med. 2000 Apr 20;342(16):1163-70. Abstract | Full Text
3. ↑ Christenson J, Innes G, McKnight D et al. Safety and efficiency of emergency department assessment of chest discomfort. CMAJ. 2004 Jun 8;170(12):1803-7. Abstract | Full Text
4. ↑ Collinson PO, Premachandram S, Hashemi K. Prospective audit of incidence of prognostically important myocardial damage in patients discharged from emergency department. BMJ. 2000 Jun 24;320(7251):1702-5. Abstract | Full Text
5. ↑ Challa PK, Smith KM, Conti CR. Initial presenting electrocardiogram as determinant for hospital admission in patients presenting to the emergency department with chest pain: a pilot investigation. Clin Cardiol. 2007 Nov;30(11):558-61. Abstract
6. ↑ Pedrazzini G, Santoro E, Latini R et al; GISSI-3 Investigators. Causes of death in patients with acute myocardial infarction treated with angiotensin-converting enzyme inhibitors: findings from the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto (GISSI)-3 trial. Am Heart J. 2008 Feb;155(2):388-94. Epub 2007 Dec 19. Abstract
7. ↑ Afilalo J, Majdan AA, Eisenberg MJ. Intensive statin therapy in acute coronary syndromes and stable coronary heart disease: a comparative meta-analysis of randomised controlled trials. Heart. 2007 Aug;93(8):914-21. Epub 2007 Feb 3. Abstract
8. ↑ Hannan EL, Racz MJ, Walford G et al. Long-term outcomes of coronary-artery bypass grafting versus stent implantation. N Engl J Med. 2005 May 26;352(21):2174-83. Abstract | Full Text
9. ↑ World Health Organization: Cardiovascular disease: prevention and control.

External Links

Organizations

American Heart Association: Home Page

American College of Cardiology: Home Page

NHLBI Resources

• Act in Time to Heart Attack Signs
• Cardiovascular Information for the Public
• “Your Guide to a Healthy Heart”
• “Your Guide to Living Well With Heart Disease”

Non-NHLBI Resources

• Angina: Interactive Tutorial (MedlinePlus)
• Heart Attack: Interactive Tutorial (MedlinePlus)

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2. Content from Harvard Medical School