What are the criteria for a pathological Q (quantum) wave?

Criteria for Pathological Q Waves on ECG

Pathological Q waves are defined as any Q wave in leads V2–V3 ≥0.02 sec or QS complex in leads V2 and V3, or Q wave ≥0.03 sec and ≥0.1 mV deep or QS complex in leads I, II, aVL, aVF or V1–V6 in any two leads of a contiguous lead grouping. 1

Specific Criteria for Pathological Q Waves

• Duration and Depth Requirements:

  • In leads V2-V3: Q wave ≥0.02 sec or QS complex
  • In leads I, II, aVL, aVF, V1-V6: Q wave ≥0.03 sec and ≥0.1 mV deep or QS complex
  • Must be present in at least two leads of a contiguous lead grouping 1

• Lead Groupings for Assessment:

  • Anterior: V1-V4
  • Inferior: II, III, aVF
  • Lateral: V5, V6, I, aVL 1, 2

Normal Q Wave Variants (Non-Pathological)

• QS complex in lead V1 (normal variant)
• Q wave <25% of R wave amplitude in lead III
• Q wave in aVL if frontal QRS axis is between 60° and 90°
• Small septal Q waves in leads I, aVL, aVF, and V4–V6 1

Clinical Significance and Diagnostic Value

• The "classic" criteria for Q waves show the strongest correlation with infarct size as measured by cardiac magnetic resonance imaging 3
• Q waves reliably predict MI location, size, and transmural extent primarily in anterior infarctions 2, 4
• Even small Q waves (<40-ms duration and <0.5-mV amplitude) in V2 or V3 significantly predict the presence of coronary artery disease, particularly left anterior descending artery stenosis 5
• The presence of Q waves is determined more by total infarct size than by transmural extent 4

Special Considerations

• Population-Specific Variations:

  • In adolescents <16 years, borderline Q waves in anterior leads may represent a normal "juvenile pattern"
  • In Black athletes, borderline Q waves in anterior leads may be a normal variant, especially with J-point elevation and convex ST-segment elevation
  • Pathological Q waves are reported in approximately 1-2% of all athletes, with higher prevalence in males and Black athletes 1

• Potential Pitfalls:

  • Lead misplacement, especially in V1-V2, can result in false positives
  • Isolated Q waves in lead III may be normal, especially without repolarization abnormalities
  • Q waves in multiple inferior leads warrant investigation as they cannot be attributed to physiological remodeling 1

Non-Ischemic Causes of Q Waves

• Cardiomyopathy (hypertrophic, dilated, stress, cardiac amyloidosis)
• Conduction disturbances (LBBB, left anterior hemiblock, pre-excitation syndromes, ventricular pacing)
• Ventricular hypertrophy (left and right)
• Myocarditis
• Acute cor pulmonale
• Hyperkalemia 1

Evaluation Approach for Q Waves

1. Apply pathological criteria (duration, depth, distribution)
2. Consider clinical context and patient demographics
3. Evaluate for normal variants based on lead location and patient characteristics
4. For borderline or concerning Q waves:
   • Perform echocardiography (minimum evaluation)
   • Consider cardiac MRI if echocardiogram is normal but clinical suspicion remains
   • Consider stress testing for patients ≥30 years with risk factors for CAD 1

The use of Q/R ratio helps normalize Q wave depth to the degree of proceeding R-wave voltage, which can reduce false positives in athletes with physiological left ventricular hypertrophy 1.