Non-ST Segment Myocardial Infarction Overview

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.

Understanding 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 when you exert yourself), unstable angina can occur anytime and is considered more serious. Despite its symptoms, unstable angina does not cause permanent damage to the heart.
  • 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. While the symptoms can be the same as STEMI, the damage to the heart will be far less extensive.

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

Differentiating NSTEMI From STEMI

Diagnosis of NSTEMI is typically made when a person has symptoms of unstable angina. We 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 we 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 will still consider it a heart attack (some might say a "mild" heart attack). With that being said, NSTEMI has more in common with unstable angina and, as such, usually has better outcomes.

NSTEMI is rarely a precursor to STEMI due to different mechanisms of action. NSTEMI is more likely to occur in patients with diffuse coronary disease who often have collateral vessel development, while STEMI patients are less likely to have the same sort of diffuse disease or collateral vessel development.

Emergency Treatment

Treatment of NSTEMI is identical to that of unstable angina. If a person appears with 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, a condition in which the heart is not getting enough oxygen, causing cell death. This is done, in part, by administering beta blockers to prevent damage caused by the excessive production of adrenaline and high-dose statins to stabilize ruptured plaque and reduce arterial inflammation. The use of these drugs will usually alleviate cardiac ischemia within minutes. Oxygen and morphine will typically be given to assist respiration and reduce pain.
  • Stopping blood clot formation involves the use of aspirin, Plavix, and other medications to thin the blood and prevent the clumping of platelets. It also includes the avoidance of "clot busters," typically used in STEMI, which can make things worse.

What Happens Once the Condition Is Stabilized

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 percent
  • 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 the person has two or fewer of these risk factors (TIMI score 0-2), the need for further intervention can often be avoided. If the score is higher, the cardiologist may want to perform a cardiac catheterization with angioplasty and stenting.

For persons who decline invasive treatment, a stress test will typically be performed prior to discharge. If there are any signs of continued cardiac ischemia, invasive therapy will be strongly advised.

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