What are the diagnostic criteria for Non-ST-Elevation Myocardial Infarction (NSTEMI)?

Diagnostic Criteria for Non-ST-Elevation Myocardial Infarction (NSTEMI)

NSTEMI is diagnosed by the presence of elevated cardiac troponin values with at least one value above the 99th percentile upper reference limit in the setting of acute chest pain or ischemic symptoms, without persistent ST-segment elevation on ECG.

Key Diagnostic Components

1. Clinical Presentation

• Acute chest pain or discomfort (typically retrosternal)
• May present with:
  • Pressure, heaviness, or squeezing sensation
  • Radiation to left arm, neck, or jaw
  • Associated symptoms: dyspnea, diaphoresis, nausea, fatigue
• Pain may be similar to stable angina but more severe or prolonged
• Some patients (especially elderly, diabetics, or women) may present with atypical symptoms or even without chest pain

2. ECG Findings

• Absence of persistent ST-segment elevation
• May show:
  • Transient ST-segment elevation (resolving before diagnosis)
  • ST-segment depression
  • T-wave inversions
  • Non-specific ST-T wave changes
  • Normal ECG (does not exclude diagnosis)

3. Cardiac Biomarkers

• Essential criterion: Elevated cardiac troponin (preferably high-sensitivity)
  • At least one value above the 99th percentile upper reference limit
  • Serial measurements showing a rise and/or fall pattern
• Troponin is the preferred biomarker due to high cardiac specificity and clinical sensitivity 1
• Serial measurements (0h, 1h, 2h, 3h) improve diagnostic accuracy

4. Imaging

• Echocardiography: May show regional wall motion abnormalities
• Coronary angiography: Often shows severe obstructive but incompletely occlusive coronary lesions 1
• CCTA (Coronary Computed Tomography Angiography): Alternative to invasive angiography in low-to-intermediate risk patients 1

Differential Diagnosis from Other ACS Types

NSTEMI vs. Unstable Angina

• NSTEMI: Elevated cardiac troponin indicating myocardial necrosis
• Unstable Angina: No elevation of cardiac troponin despite ischemic symptoms 1

NSTEMI vs. STEMI

• NSTEMI: No persistent ST-segment elevation on ECG
• STEMI: Persistent ST-segment elevation or new LBBB on ECG 1

Risk Stratification

After diagnosis, risk stratification is essential using:

• GRACE or TIMI risk scores
• Presence of hemodynamic instability
• Recurrent symptoms/ischemia
• Presence of heart failure or serious arrhythmias
• Extent of ECG changes
• Magnitude of troponin elevation 1

Common Pitfalls to Avoid

1. Missing the diagnosis in patients with normal ECG: Up to 15% of patients with proven NSTE-ACS have normal or nearly normal coronary arteries on angiography 1

2. Delayed diagnosis in patients with atypical presentations: Women, elderly, and diabetics often present without classic chest pain

3. Overlooking NSTEMI with total coronary occlusion: Approximately 30% of NSTEMI cases involve a totally occluded coronary artery that may benefit from urgent revascularization 2

4. Premature discharge of patients with initially negative troponin: Serial measurements are essential as a single negative test does not exclude NSTEMI

5. Failure to recognize NSTEMI equivalents: Such as multilead ST depression with ST-elevation in aVR, which may indicate left main or three-vessel disease

Remember that the diagnosis of NSTEMI requires integration of clinical presentation, ECG findings, and cardiac biomarker results. No single element is sufficient for diagnosis, and the absence of one element does not exclude the diagnosis when other criteria are met.