Non-ST Segment Myocardial Infarction Overview

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Non-ST segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI) are both commonly known as heart attack. NSTEMI is the less common of the two, accounting for around 30 percent of all heart attacks.

NSTEMI, STEMI, and a third condition called unstable angina are all forms of acute coronary syndrome (ACS). For its part, ACS is defined as any condition brought on by a sudden reduction or blockage of blood flow to the heart.

Types of Acute Coronary Syndrome

All forms of ACS are usually caused by the rupture of plaque in a coronary artery, leading to either partial or complete obstruction of the vessel. Depending on the severity of the obstruction, ACS can be classified into three different types.

types of acute coronary syndrome
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  • Unstable angina is the partial rupture of an artery that causes chest pains. Unlike stable angina (which occurs during exertion), unstable angina can occur anytime and is considered more serious. Unstable angina doesn't cause permanent heart damage.
  • In STEMI, which is considered a "classic" heart attack, the ruptured plaque completely or near completely blocks a major coronary artery, resulting in extensive heart damage.
  • In NSTEMI, considered the "intermediate" form of ACS, a blockage either occurs in a minor coronary artery or causes partial obstruction of a major coronary artery. Symptoms can be the same as STEMI but the heart damage is far less extensive.

NSTEMI and unstable angina will often progress to a "complete" heart attack within the space of a few hours to a few months.


A diagnosis of NSTEMI is typically made when the person has symptoms of unstable angina.

Doctors can differentiate STEMI from NSTEMI via readings on an electrocardiogram (ECG) in the so-called "ST-segment." Under normal conditions, the ST-segment is the flat line you see on an ECG between heartbeats.

During a heart attack, the ST-segment is raised. As such, NSTEMI gets its name because there is no evidence of ST-segment elevation.

Because NSTEMI causes damage to the heart muscle, doctors still consider it a heart attack (some might say a "mild" heart attack). Even so, NSTEMI has more in common with unstable angina and, as such, usually has better outcomes.

NSTEMI rarely leads to STEMI because they have different mechanisms of action. NSTEMI is more likely in people with diffuse coronary disease, who often have collateral vessel development. People with STEMI are less likely to have that sort of diffuse disease or collateral vessel development.

Emergency Treatment

NSTEMI treatment is identical to that for unstable angina. If you have cardiac symptoms (chest tightness, clamminess of the skin, shooting pains in the left arm, etc.), the doctor will begin intensive therapy to stabilize the heart and prevent further damage.

Stabilization will primarily focus on two things: eliminating acute ischemia and stopping blood-clot formation.

Acute ischemia: In this condition, the heart doesn't enough oxygen, which causes cell death. Doctors eliminate it in part by using beta blockers and high-dose statins.

Beta blockers prevent damage caused by excessive adrenaline, while statins stabilize ruptured plaque and reduce arterial inflammation. These drugs will usually alleviate cardiac ischemia within minutes.

Oxygen and morphine may be given to assist respiration and reduce pain.

Stopping blood clot formation: This involves the use of aspirin, Plavix, and other medications to thin the blood and prevent the clumping of platelets.

This treatment does not include "clot busters," typically used in STEMI, which can make things worse.

After Stabilization

Once the patient is stabilized, the doctor will assess whether additional interventions are needed. Many cardiologists will use a TIMI (thrombosis in myocardial infarction) score to determine the likely outcome for the individual.

The TIMI score assesses whether the person has any of the following risk factors:

  • Age 65 years or older
  • Presence of at least three risk factors for coronary heart disease
  • Prior coronary blockage of greater than 50%
  • ST-segment deviation on the admission ECG
  • At least two angina episodes in the past 24 hours
  • Elevated cardiac enzymes
  • Use of aspirin within the past seven days

If you have two risk factors or less (TIMI score 0-2), you may not need further intervention. If the score is higher, the cardiologist may want to perform a cardiac catheterization with angioplasty and stenting.

If someone declines invasive treatment, a stress test will typically be performed prior to their leaving the hospital. If that shows any signs of continued cardiac ischemia, invasive therapy will be strongly advised.

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