Harvard Health Letters

Harvard Health Letters

The term "heart attack" does an excellent job conveying the severity of an all-too-common event. But it hides a remarkable diversity of medical emergencies that differ in cause, geography, consequences, and initial treatment.

We use "heart attack" as shorthand for myocardial infarction (MI) -- an interruption of blood flow to part of the heart muscle that damages or destroys a swath of heart cells. Here's a guide to the names that doctors give to different types of heart attacks:

Acute coronary syndrome

Doctors lump heart attacks into an even larger category called acute coronary syndrome that also includes unstable angina. These are conditions caused by acute myocardial ischemia (iss-KEY-me-uh) -- a suddenly inadequate blood supply to part of the heart muscle. Acute coronary syndromes are diagnosed based on:

Symptoms such as sudden pain in the chest, jaw, or upper back or arm; shortness of breath; vomiting; heavy sweating; or clammy skin.

Electrocardiogram (ECG) tracings that include departures from the normal tracing, such as an elevation in the ST segment or a depression in the Q wave.

Blood tests to measure troponins (troe-POE-ninz) and creatine kinase, proteins that are released into the bloodstream when cardiac muscle is damaged.

There are three types of acute coronary syndrome: ST-segment elevation myocardial infarction (STEMI), non-ST-segment myocardial infarction (NSTEMI), and unstable angina. They represent a spectrum of harm from significant injury to heart muscle (STEMI) to no immediate injury but a high probability of an impending heart attack (unstable angina).

A heart attack (myocardial infarction) occurs when blood flow to part of the heart muscle is blocked. A complete blockage can damage a large portion of heart muscle, as in the transmural myocardial infarction shown above.

Riding the waves

Changes on an ECG are often a tip-off that myocardial infarction is under way.

STEMI. In an ST-segment elevation myocardial infarction, a coronary artery is completely blocked by cholesterol-filled plaque or by a blood clot. Deprived of oxygen and energy, heart muscle cells supplied by the blocked artery begin to shut down key functions, then begin to die. On an ECG, a complete blockage appears as an elevated ST segment. Ideally, a STEMI is treated immediately with artery-opening angioplasty plus a stent or clot-busting drugs.

NSTEMI. In a non-ST-segment elevation myocardial infarction, a blood clot partly blocks the artery, and the ensuing ischemia doesn't affect the entire thickness of that zone of heart muscle. As a result, the damage isn't as apparent on an ECG as it is with a STEMI. After a few hours of observation, though, increases in troponins or creatine kinase will reveal damage to the heart muscle. Some NSTEMIs are treated with the same urgency as STEMIs, others aren't.

Unstable angina

Unstable angina is chest pain that tends to happen at rest, lasts a while, and isn't quelled by nitroglycerin. The most common trigger of unstable angina is the bursting of a cholesterol-filled plaque in the lining of a coronary artery. As the plaque's toxic contents spew into the bloodstream, a clot forms to plug the spill. The rupture and clot block blood flow, but not completely.

Chest pain or other symptoms come and go as the clot grows and as the body's natural clot busters try to melt it away. Think of unstable angina as an overture to a heart attack. Sometimes unstable angina resolves peacefully; sometimes it crescendoes into a full-blown heart attack. There is a fine line between unstable angina and a NSTEMI. Treatment of unstable angina can range from medications to interventions such as angioplasty or bypass surgery.

Q-wave heart attack

If a coronary artery is blocked for a long time and the area of muscle it nourishes is poorly supplied by smaller surrounding blood vessels, the blockage will likely cause the death of cells throughout the entire thickness of the heart muscle. Such heart attacks tend to create deep depressions in the Q wave on an ECG, so they were once called Q-wave myocardial infarctions. That term is being replaced with transmural myocardial infarction. STEMIs sometimes become Q-wave heart attacks.

Non-Q-wave heart attack

Less extensive attacks that damage just the inner or the outer section of heart muscle have little effect on the Q wave. Today these are called subendocardial infarctions, a term that overlaps with NSTEMI.

MI geography

A heart attack is sometimes named by the section of heart muscle it damaged.

Anterior heart attacks affect the front part of the heart, usually the left ventricle. Anterior MIs are sometimes big heart attacks that stem from blockage of the left anterior descending artery.

Inferior heart attacks affect the bottom portion of the heart. These are generally caused by complete blockage of the right coronary artery.

Lateral myocardial infarctions harm one side of the heart. They tend to stem from a blockage in the left circumflex artery or the lateral branch of the left anterior descending artery.

Transmural means that the damage extends though the entire thickness of the heart muscle, from inside to out.

A subendocardial attack involves only one-third to one-half of the muscle along the inner layer of the left ventricle.

Silence isn't always golden

Silent heart attacks are episodes in which blockage of a coronary artery damages part of the heart muscle but without causing any symptoms or generating ones that are so subtle they go unnoticed or are ignored. A silent heart attack is usually discovered when a person undergoes an electrocardiogram or echocardiogram for a different reason and the test shows abnormalities suggestive of damage to the heart.


The type of heart attack determines its initial treatment. Once the immediate danger has passed, the follow-through is the same for all -- a lifelong emphasis on exercise, a healthful diet, medications, stress reduction, and other strategies that protect the heart and arteries. - Harvard Heart Letter


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Health - Heart Attacks Come in All Kinds and Sizes