Is this ECG pattern indicative of an old myocardial infarction (MI) in an adult patient with a history of cardiovascular disease?

ECG Diagnosis of Old Myocardial Infarction

Pathological Q waves ≥0.03 seconds in duration and ≥0.1 mV in depth, present in at least two contiguous leads, are the hallmark ECG finding of old MI and indicate prior transmural infarction. 1, 2

Primary Diagnostic Criteria for Old MI

The most specific ECG findings for established myocardial infarction include:

• Pathological Q waves defined as duration ≥0.04 seconds (40 milliseconds) that suggest prior MI and indicate high likelihood of significant coronary artery disease 3, 1
• Q/R ratio ≥0.25 or Q waves ≥40 ms in two or more contiguous leads (except III and aVR) 2
• QS complexes (complete absence of R wave) particularly in leads V1-V3, which may represent septal or anterior infarction 1, 2

Territory-Specific Patterns

Anterior MI

• Pathological Q waves in leads V1-V4 with duration ≥0.03 seconds and depth ≥0.1 mV reliably predict anterior MI location, size, and transmural extent 1, 4
• Q waves in anterior leads correlate strongly with anterior MI size (r=0.70) and transmural extent (r=0.70) 4
• Loss of R wave progression across precordial leads with reduced R-wave amplitude 1

Inferior MI

• Q waves in leads II, III, and aVF indicate inferior wall involvement, though isolated Q waves in lead III alone may be normal 3, 1
• Inferior Q waves show weaker correlation with MI size (r=0.35) compared to anterior infarctions 4

Lateral/Posterior MI

• Tall R waves in V1-V2 (≥0.04 seconds duration with R/S ratio >1) are more powerful predictors of lateral MI than lateral Q waves themselves 3, 4
• Q waves in leads I, aVL, V5-V6 suggest lateral involvement but correlate weakly with lateral MI size (r=0.33) 4

Associated Chronic Findings

Beyond Q waves, old MI may demonstrate:

• Persistent T-wave inversions in leads with Q waves that may remain for weeks, months, or indefinitely after the acute event 5, 1
• Persistent ST-segment elevation suggesting left ventricular aneurysm formation 3, 1
• Reduced R-wave amplitude in affected territories compared to expected normal values 1

Critical Diagnostic Pitfalls to Avoid

Normal variants that mimic pathological Q waves:

• QS complex in lead V1 alone is normal and should not be interpreted as septal infarction 1, 2
• Small septal Q waves <0.03 seconds and <25% of R-wave amplitude are normal in leads I, aVL, aVF, and V4-V6 2
• Q waves in lead III <0.03 seconds and <25% of R-wave amplitude are normal if frontal QRS axis is between 0° and 30° 1, 2
• Q waves in aVL may be normal if frontal QRS axis is between 60° and 90° 2

Non-ischemic causes of pathological Q waves:

• Left ventricular hypertrophy, particularly from aortic stenosis, can produce Q waves in V1-V2 with higher voltage (>1.3 mV) and more leftward horizontal QRS axis (0° to -45°) compared to true anterior MI 6
• Hypertrophic cardiomyopathy produces pathological Q waves without coronary disease 2
• Infiltrative myocardial diseases and myocardial fibrosis can cause Q waves 2
• Accessory pathways (Wolff-Parkinson-White) may produce pseudo-infarct patterns 2
• High precordial lead placement creates pseudo-septal infarct pattern 2

Essential Diagnostic Algorithm

When evaluating for old MI on ECG:

1. Compare with previous ECGs when available—this dramatically improves diagnostic accuracy for distinguishing old from new findings 3, 1
2. Measure Q wave duration and depth in all leads, requiring ≥0.03-0.04 seconds and ≥0.1 mV in two contiguous leads 1, 2
3. Assess for territory-specific patterns: anterior Q waves are most reliable, while tall R waves in V1-V2 better indicate posterior/lateral MI 4
4. Exclude normal variants by checking QRS axis and lead-specific criteria 1, 2
5. Consider alternative diagnoses including LVH, cardiomyopathy, and lead misplacement, particularly if Q waves are isolated to V1-V2 2, 6
6. Integrate clinical context—the ECG alone is often insufficient and must be interpreted alongside clinical history and cardiac biomarkers 1

Prognostic Implications

• Established Q waves ≥0.04 seconds indicate high likelihood of significant coronary artery disease even in the absence of acute symptoms 3
• Patients with persistent T-wave inversions in leads with Q waves at 12 months post-MI have worse left ventricular function and greater myocardial damage than those whose T waves normalized 7
• The number and distribution of Q waves across multiple territories indicates larger infarct size and worse prognosis 3, 4