Can a non-ST-elevation myocardial infarction (NSTEMI) occur with no electrocardiogram (ECG) changes?

Can a Non-ST-Elevation Myocardial Infarction (NSTEMI) Occur Without ECG Changes?

Yes, a non-ST-elevation myocardial infarction (NSTEMI) can definitely occur without ECG changes, as the diagnosis of NSTEMI is primarily based on elevated cardiac troponin levels in the appropriate clinical context, not on ECG findings. 1

Diagnostic Criteria for NSTEMI

• According to the Universal Definition of Myocardial Infarction, NSTEMI is diagnosed by the detection of a rise and/or fall of cardiac troponin with at least one value above the 99th percentile upper reference limit, along with at least one of the following 1:

  • Symptoms of myocardial ischemia
  • New ischemic ECG changes
  • Development of pathological Q waves
  • Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality
  • Identification of an intracoronary thrombus

• Importantly, while ECG changes are one criterion, they are not mandatory for diagnosis if other criteria are met 1

ECG Findings in NSTEMI

• Common ECG findings in NSTEMI include 2:

  • ST-segment depression (≥0.5 mm)
  • T-wave inversion (≥2 mm), especially when symmetrical and deep
  • Nonspecific ST-segment and T-wave changes
  • Established Q waves indicating prior MI

• However, up to 25% of patients with confirmed NSTEMI may have a normal or non-diagnostic ECG at presentation 2

• The absence of ECG changes does not rule out NSTEMI when clinical suspicion is high 1

Clinical Implications

• Patients with normal ECGs but elevated troponins still have significant risk for adverse outcomes 2:

  • One-year incidence of death or new MI is 8.2% for patients with no ECG changes compared to 16.3% with ≥0.5 mm ST-segment deviation 2

• The 2014 AHA/ACC guidelines emphasize that "a completely normal ECG in a patient with chest pain does not exclude ACS, because 1% to 6% of such patients will have a MI, and at least 4% will have UA" 1

Special Considerations

• Left circumflex coronary artery occlusions frequently present with non-diagnostic ECGs 2, 3

• Posterior wall infarctions may have subtle or no anterior lead changes 2

• Serial ECGs increase diagnostic sensitivity, as some changes may be transient 2

• Certain patient populations (elderly, diabetics, women) are more likely to present with atypical symptoms and non-diagnostic ECGs 1

Diagnostic Approach

• For patients with suspected ACS but no ECG changes 1:

  • Serial cardiac troponin measurements are essential (at presentation and 3-6 hours after symptom onset) 1
  • Additional troponin levels beyond 6 hours may be necessary when clinical suspicion remains high despite normal initial values 1
  • If symptom onset time is unclear, the time of presentation should be considered the starting point 1

• Risk stratification tools like GRACE or TIMI scores should be used regardless of ECG findings 1

Management Implications

• Patients with elevated troponins but no ECG changes should still receive appropriate ACS management 1

• The absence of ECG changes should not delay appropriate invasive or non-invasive testing when clinical suspicion for ACS is high 1

• Patients with normal ECGs but elevated troponins may still have significant coronary disease requiring intervention 4

In conclusion, while ECG changes are common in NSTEMI, their absence does not exclude the diagnosis when cardiac biomarkers are elevated in the appropriate clinical context. Clinicians should maintain a high index of suspicion and rely on the complete clinical picture rather than ECG findings alone.