What is Segment Elevation Myocardial Infarction (STEMI)?

What You Need to Know about Heart Attacks

Heart attack
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ST Segment Elevation Myocardial Infarction (STEMI) is the name cardiologists currently use to describe a classic heart attack.

“Myocardial infarction,” or heart attack, refers to the death of a portion of the heart muscle (myocardium) caused by blood flow interruption. “ST segment elevation” refers to a particular pattern seen on the electrocardiogram (ECG), often seen when a substantial part of the heart muscle is dying.

What Causes a STEMI?

A STEMI is the most severe of the three types of Acute Coronary Syndrome (ACS). ACS occurs when an atherosclerotic plaque ruptures in a coronary artery. The rupture causes blood clots to form inside the artery, which often leads to the partial or complete occlusion of the artery.

The heart muscle being supplied by the occluded artery begins to suffer from ischemia (lack of oxygen), which can manifest as angina (chest discomfort). If the blockage is severe enough heart muscle begins to die, and a myocardial infarction occurs.

Sometimes with ACS, the clot will come and go over a period of hours or days, without blocking the artery enough to cause cell death. This type of ACS is called unstable angina.

Sometimes ACS causes nearly complete occlusion - but not total occlusion - of the coronary artery. Cell death occurs, but some of the heart muscle supplied by the artery survives.

Because the ST segment on the ECG does not become elevated in this condition, it is called a non-ST-segment elevation myocardial infarction, or NSTEMI.

When the blood clot that forms during ACS completely blocks the artery, all the heart muscle supplied by the artery begins to die. This, the most severe consequence of an ACS, is called a STEMI.

In many cases, a STEMI is preceded (by hours, days or weeks) by unstable angina and/or an NSTEMI.

With any type of ACS, the death of heart muscle either occurs acutely or is likely to occur in the very near future. So ASC is always a medical emergency and always requires immediate and aggressive medical care.

What are the Symptoms of STEMI?

Classically, a STEMI is accompanied by intense pain or pressure in or around the chest, which often radiates to the neck, jaw, shoulder or arm. Profuse sweating and breathlessness are also common, as is a frightening sense of doom.

However, heart attack symptoms may be substantially more subtle than this classic pattern, and anyone who is at risk for coronary artery disease should pay attention to any unusual symptoms arising anywhere above the waist.

How is a STEMI Diagnosed?

In most cases the diagnosis of a STEMI can be made relatively quickly once the patient is under medical care. Symptoms compatible with a heart attack, accompanied by the classic pattern of ST segment elevation on the ECG, is usually enough for a doctor to initiate treatment.

Cardiac enzymes are invariably elevated during a STEMI, but the diagnosis can usually be made before the lab results are available.

What are the Consequences of a STEMI?

An acute heart attack, in addition to the pain and distress it causes, can cause sudden death from ventricular fibrillation or from acute heart failure. After a heart attack is completed, the patient may be left with a substantially damaged heart muscle that can produce chronic heart failure, as well as an increased risk of dangerous cardiac arrhythmias.

To prevent such acute and long-term problems, it is critical for anyone who thinks they might be having a heart attack to call 911 immediately.

How is a STEMI Treated?

The moment a STEMI is diagnosed, treatment is begun. In addition to administering several drugs to attempt to stabilize the heart muscle - including oxygen, morphine, beta blockers and a statin - steps are taken immediately to open up the blocked artery.

Quickly unblocking the coronary artery is critical; every minute counts. Unless the artery is opened within three hours of the occlusion, at least some permanent damage to the heart muscle will result. Much of the damage can be prevented for up to six hours and some of the damage can be prevented for up to 12 hours. But every minute counts.

There are two general approaches to opening up an occluded coronary artery - the use of thrombolytic therapy (“clot-busting” drugs), or immediate angioplasty and stenting. But whichever method is chosen, the important thing is to get the artery opened rapidly.

Once the acute phase of treatment is over and the blocked artery is opened, there is still a lot that has to be done to stabilize the heart, and to reduce the odds of another heart attack.


O'Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2013; 127:529.

Goodman SG, Menon V, Cannon CP, et al. Acute ST-segment elevation myocardial infarction: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest 2008; 133:708S.

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