What is the abnormal electrocardiogram (ECG) finding most consistent with myocardial ischemia in a patient with suspected coronary artery disease (CAD) and symptoms such as chest pain or shortness of breath?

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ST-Segment Depression and/or T-Wave Inversion is Most Consistent with Myocardial Ischemia

ST-segment depression ≥0.5 mm (0.05 mV) and/or T-wave inversion are the most reliable electrocardiographic indicators of myocardial ischemia in patients with suspected coronary artery disease. 1, 2

Why ST-Segment Depression and T-Wave Inversion Are the Correct Answer

ST-Segment Depression Criteria

  • Horizontal or down-sloping ST-segment depression ≥0.5 mm (0.05 mV) in two or more contiguous leads is highly suggestive of acute coronary syndrome in the appropriate clinical context 1, 2
  • The magnitude of ST depression correlates directly with risk—greater depression (≥2 mm) indicates more extensive coronary artery disease and worse prognosis 1, 2, 3
  • Transient ST-segment changes (≥0.05 mV) that develop during symptomatic episodes and resolve when asymptomatic strongly suggest acute ischemia and severe underlying CAD 1, 4

T-Wave Inversion Significance

  • Deep symmetrical T-wave inversion (≥2 mm or 0.2 mV), particularly in precordial leads, strongly suggests acute ischemia, often due to critical stenosis of the left anterior descending coronary artery 1, 4
  • Marked symmetrical precordial T-wave inversion identifies patients at high risk who often exhibit anterior wall hypokinesis 1
  • T-wave inversion in leads with predominant R-waves is a reliable indicator of unstable coronary disease, though less specific than ST-segment depression 1

Prognostic Value

  • The one-year incidence of death or new MI is 16.3% with ≥0.5 mm ST-segment deviation compared to 8.2% for no ECG changes 4
  • The sum of ST-segment depression across all leads is a powerful independent predictor of 30-day mortality, with continuous increase in risk as the extent of depression increases 3
  • ST-segment depression and T-wave inversion are independent predictors of new onset heart failure within 30 days of presentation 5

Why the Other Options Are Incorrect

Peaked T-Waves in All Leads (Option 1)

  • Peaked T-waves are not characteristic of myocardial ischemia 1
  • This finding is typically associated with hyperkalemia or hyperacute phase of STEMI (not the question's focus on general ischemia) 6

Prolonged QT Interval (Option 3)

  • Prolonged QT interval is not a primary indicator of myocardial ischemia 1
  • This finding relates to repolarization abnormalities from medications, electrolyte disturbances, or congenital syndromes 4

Sinus Bradycardia (Option 4)

  • Sinus bradycardia is not a specific indicator of myocardial ischemia 1
  • While it may occur with inferior MI (due to vagal stimulation or involvement of the SA node), it is not diagnostic of ischemia itself 1

Clinical Application Algorithm

When Evaluating for Myocardial Ischemia:

  1. Obtain 12-lead ECG within 10 minutes of presentation with chest pain or anginal equivalents 4
  2. Look specifically for ST-segment depression ≥0.5 mm in two or more contiguous leads 1, 2
  3. Assess for T-wave inversion ≥2 mm, particularly deep symmetrical inversion in precordial leads 1, 4
  4. Compare with prior ECG if available—this significantly improves diagnostic accuracy 1, 4
  5. Obtain serial ECGs at 15-30 minute intervals if initial ECG is non-diagnostic but clinical suspicion remains high 4

Risk Stratification Based on ECG Findings:

  • Highest risk: ST-segment depression in ≥3 leads with maximal depression ≥2 mm 1, 3
  • High risk: Deep symmetrical T-wave inversion in anterior leads (suggests critical LAD stenosis) 1, 4
  • Moderate risk: ST-segment depression 0.5-2 mm in fewer leads 2

Critical Pitfalls to Avoid

  • Do not dismiss non-specific ST-segment and T-wave changes (ST deviation <0.5 mm or T-wave inversion ≤2 mm)—while less diagnostically helpful, they may still indicate ischemia 1, 4
  • A completely normal ECG does not exclude acute coronary syndrome—1-6% of patients with normal ECGs will have MI, and at least 4% will have unstable angina 4
  • Consider alternative causes of ST-segment and T-wave changes: LV hypertrophy, bundle branch block, pericarditis, myocarditis, Takotsubo cardiomyopathy, electrolyte abnormalities, and certain medications (tricyclic antidepressants, phenothiazines) 4, 2
  • ST-segment depression in leads V1-V3 may indicate posterior wall MI—consider obtaining posterior leads (V7-V9) 1, 4
  • Left circumflex occlusion can present with a non-diagnostic 12-lead ECG—maintain high clinical suspicion despite unremarkable ECG 4

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

ECG Criteria for Ischemic ST Depression

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

4
Guideline

ECG Changes in Non-ST-Elevation Myocardial Infarction (NSTEMI)

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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