NSTEMI: Non-ST-Segment Myocardial Infarction

Why even a "mild" heart attack can be a big deal

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Non-ST segment elevation myocardial infarction (NSTEMI) is one of the three types of acute coronary syndrome (ACS). Like all forms of ACS, NSTEMI is considered to be a medical emergency.

What Is an NSTEMI?

All forms of ACS are usually caused by the rupture of an atherosclerotic plaque in a coronary artery, producing at least some degree of obstruction of the artery. Depending on the severity of the obstruction, and the subsequent damage to the heart muscle supplied by the affected artery, ACS is classified into three different types.

In increasing order of severity, these three types are:

• Unstable angina

• NSTEMI

• STEMI (ST Segment Elevation Myocardial Infarction)

In unstable angina, partial rupture of a coronary artery produces symptoms of angina that occur in an "unstable" or accelerated pattern. Most often, people with unstable angina have chest discomfort that occurs at rest; or that occurs as a new symptom that significantly limits physical activity; or that is a significant worsening in previous stable angina (usually, occurring much more frequently or with notably less exertion than before). Despite these symptoms, in people with unstable angina there is no evidence of permanent damage to cardiac muscle cells.

In STEMI (which is essentially a classic heart attack), the ruptured plaque completely (or nearly completely) occludes the artery, and the resulting heart muscle damage is often extensive. With a STEMI the electrocardiogram (ECG) shows characteristic changes; namely, the ST segment portion of the ECG is grossly elevated.

Also, blood levels of the cardiac biomarkers (formerly called cardiac enzymes) are significantly elevated, indicating extensive damage to the heart muscle. 

In NSTEMI, which is considered the "intermediate" form of ACS, symptoms are identical to those of unstable angina. The only feature that distinguishes between unstable angina and NSTEMI is that with an NSTEMI, cardiac biomarkers are elevated to some extent, indicating that at least some cardiac cell damage has occurred.

To say it another way, with both unstable angina and NSTEMI the coronary artery blockage is not (yet) complete, and the damage to heart cells (if any) is relatively small. In contrast, with a STEMI, the blockage is complete or nearly complete, and cardiac damage is much more extensive.

Very often, both unstable angina and NSTEMI will progress to a "completed" heart attack, that is, to a STEMI. The time frame in which this may occur varies from a matter of hours to a matter of months. 

Because NSTEMI (and unstable angina) are often precursors to a STEMI, these conditions need to be treated aggressively, even after the acute episode has resolved.

How Is NSTEMI Diagnosed?

The diagnosis of NSTEMI is made when a person has the symptoms of unstable angina, has no ST-segment elevation on the ECG, and has an elevation in cardiac biomarkers, indicating that heart cell damage is occurring.

Because there is indeed heart muscle damage with an NSTEMI, doctors consider it to be a "heart attack." (Most often, they will call it a "mild" heart attack.) Still, it is useful to keep in mind that NSTEMI actually has much more in common with unstable angina than it does with a STEMI (a "classic" heart attack).

So, if you or a loved one are told you have had a heart attack, it is important to ask your doctor to be more precise — which was it, a STEMI or an NSTEMI?

Furthermore, it is important to realize that the lab tests that measure cardiac biomarkers are becoming more and more sensitive. This allows doctors to detect substantially smaller amounts of heart muscle damage than they could have detected in the recent past. And this means that many people who would have been diagnosed with unstable angina just a few years ago are now being diagnosed with NSTEMI. (This fact should be taken into account when we hear statistics about the increasing rate of "heart attacks." Many of those "new" heart attacks may simply reflect our improved ability to measure cardiac biomarkers.)

Risk Factors for NSTEMI

NSTEMI is a manifestation of atherosclerotic heart disease, so the risk factors for developing NSTEMI are the usual cardiovascular risk factors we hear about so often. These include elevated LDL cholesterol levels, smoking, obesity, hypertensiondiabetes, and a sedentary lifestyle.

How Is NSTEMI Treated?

The treatment of NSTEMI is identical to the treatment of unstable angina.

NSTEMI and unstable angina are medical emergencies. A coronary artery has likely ruptured, and major damage to the heart muscle is at least seriously threatened. It is critical to stabilize the situation as rapidly as possible.

Accordingly, the first step in treating NSTEMI is to take steps to protect the heart muscle to prevent further damage. This can usually be accomplished by administering oxygen, morphine, beta blockers, aspirin, Plavix (a blood thinner), and a statin drug. If the person with NSTEMI cannot be stabilized within a short time with such measures, cardiac catheterization is generally performed, and the culprit plaque is treated with angioplasty and stenting.

Clot-busting drugs, which are commonly used to try to open the occluded artery in people having an acute STEMI, have been shown not to be beneficial in people with unstable angina and NSTEMI, and should be avoided.

Once a patient with NSTEMI is stabilized, the cardiologist will need to decide whether to continue with “conservative” therapy (that is, drug therapy alone) or instead to recommend invasive therapy (generally, a stent) to help prevent any further rupture of the plaque.

The decision on whether invasive therapy ought to be used generally is made by assessing several risk factors that help to predict whether a person with unstable angina or NSTEMI, once stabilized, is likely to remain stable on drug therapy alone. These risk factors include age over 64 years; the presence of hypertension, diabetes, high lipid levels, smoking history, or a strong family history of early heart disease; a prior history of a blocked coronary artery; and the level of elevation in cardiac biomarkers. If more than two of these risk factors are present, invasive therapy is likely to result in a better outcome.

A Word From Verywell

NSTEMI (non-ST segment myocardial infarction) is the intermediate form of acute coronary syndrome. While it is considered a "heart attack," it is actually very similar to unstable angina, and is treated the same way as unstable angina.

The key thing to know about NSTEMI is that, while the NSTEMI itself generally causes only a small amount of cardiac muscle damage, it indicates that an atherosclerotic plaque has partially ruptured. So, after the NSTEMI has been stabilized, it is important for the cardiologist to assess the likelihood of a complete rupture in the future, and to take definitive steps to prevent it.

Sources:

Amsterdam EA, Wenger NK, Brindis RG, et al. 2014 AHA/ACC Guideline for the Management of Patients with Non-ST-elevation Acute Coronary Syndromes: Executive Summary: a Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation 2014; 130:2354.

Thygesen, K, Alpert, JS, White, HD, et al. Universal Definition of Myocardial Infarction: Kristian Thygesen, Joseph S. Alpert and Harvey D. White on Behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction. Eur Heart J 2007; 28:2525.

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