What is Non-ST-Elevation Myocardial Infarction (NSTEMI)?

What is NSTEMI (Non-ST-Elevation Myocardial Infarction)?

NSTEMI is a type of heart attack characterized by myocardial cell death (necrosis) caused by severely obstructive but incompletely occlusive coronary artery blockage, diagnosed by elevated cardiac troponin levels above the 99th percentile in the appropriate clinical context, with ECG showing ST-segment depression, T-wave inversion, or other nonspecific changes—but notably without persistent ST-segment elevation. 1, 2

Pathophysiology

NSTEMI results from an acute imbalance between myocardial oxygen supply and demand, most commonly through the following mechanism 1:

• Atherosclerotic plaque disruption (rupture, erosion, or ulceration) occurs in a coronary artery 1
• Platelet-rich thrombus formation develops on top of the disrupted plaque, creating a "plaque + superimposed thrombus complex" 1
• Partial coronary occlusion results—the thrombus severely obstructs but does not completely occlude the artery (unlike STEMI where complete occlusion typically occurs) 1, 2
• Microembolization of platelet aggregates and plaque components travels downstream, causing patchy areas of myocardial necrosis 1
• Myocardial cell death occurs in the affected territory, releasing detectable cardiac biomarkers (troponin) into the bloodstream 1

Diagnostic Criteria

The diagnosis requires meeting all of the following criteria 1, 3:

• Elevated cardiac troponin: A rise and/or fall with at least one value above the 99th percentile upper reference limit 1
• Clinical context of myocardial ischemia: At least one of the following 1:
  • Symptoms of ischemia (typically chest pain/pressure)
  • New or presumed new significant ST-T wave changes on ECG
  • Development of pathological Q waves
  • Imaging evidence of new loss of viable myocardium
  • Intracoronary thrombus detected on angiography
• Absence of persistent ST-segment elevation on ECG 1, 2

ECG Findings

Unlike STEMI, NSTEMI does not show persistent ST-elevation but instead presents with 1, 4:

• ST-segment depression (≥0.5 mm), particularly in multiple leads—this is the hallmark finding 4
• T-wave inversion (≥2 mm), especially when symmetrical and deep in precordial leads 4
• Nonspecific ST-T wave changes (ST deviation <0.5 mm or T-wave inversion ≤2 mm) 4
• Normal ECG in some cases—a completely normal ECG does not exclude NSTEMI, as 1-6% of patients with chest pain and normal ECG will have MI 4

Critical pitfall: The ECG may be entirely normal in NSTEMI, particularly in elderly patients, diabetics, and women who often present atypically. Serial troponin measurements at presentation and 3-6 hours after symptom onset are essential when clinical suspicion remains high despite a normal initial ECG. 4

Clinical Presentation

The typical presentation includes 3:

• Chest pain or discomfort: Described as pressure, tightness, heaviness, or pain that may radiate to neck, jaw, shoulders, back, or arms 3
• Associated symptoms: Dyspnea, nausea, vomiting, diaphoresis (sweating), weakness, dizziness, or lightheadedness 3
• Atypical presentations: More common in women, elderly patients, and diabetics who may present without chest pain 2

Distinction from Other Acute Coronary Syndromes

NSTEMI sits within the acute coronary syndrome (ACS) spectrum 1, 3:

• Unstable Angina (UA): Same clinical presentation and ECG changes as NSTEMI, but cardiac biomarkers remain normal (no myocardial necrosis) 1, 3
• NSTEMI: Cardiac biomarkers elevated (myocardial necrosis present), no persistent ST-elevation 1, 2
• STEMI: Cardiac biomarkers elevated, persistent ST-elevation present on ECG, indicating complete coronary occlusion and full-thickness myocardial damage 2

Prognosis and Risk

NSTEMI carries significant prognostic implications 4, 5:

• ECG findings predict outcomes: ST-depression in ≥3 leads with maximal depression ≥0.2 mV indicates 3-4 times higher likelihood of acute MI 4
• One-year mortality/MI risk: 16.3% with ≥0.5 mm ST-segment deviation versus 6.8% for isolated T-wave changes 4
• Recurrent ischemia: Approximately 27% of patients experience recurrent ischemic episodes within the first 24-48 hours 4
• Long-term prognosis: Often poorer than STEMI due to typical comorbidity burden in older NSTEMI patients and diverse etiologies 6

Immediate Management Priorities

The initial approach within the first 10 minutes includes 2:

• 12-lead ECG acquired and interpreted within 10 minutes of first medical contact 2
• Aspirin 162-325 mg (chewed, non-enteric coated) administered immediately 1, 2, 7
• Vital signs assessment and focused history/physical examination 2
• Serial ECGs at 15-30 minute intervals if initial ECG is non-diagnostic but clinical suspicion remains high 4