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

Criteria for Pathological Q Waves

Pathological Q waves are defined as a Q/R ratio ≥ 0.25 or Q wave duration ≥ 40 ms in two or more contiguous leads (except leads III and aVR). 1

Detailed Criteria for Pathological Q Waves

According to current guidelines, the following specific criteria define pathological Q waves:

• Any Q wave in leads V2–V3 ≥ 0.02 sec or QS complex in leads V2 and V3 2
• 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 2
• R wave ≥ 0.04 sec in V1–V2 and R/S ≥ 1 with a concordant positive T wave in absence of conduction defect 2

Normal Q Waves vs. Pathological Q Waves

It's important to distinguish normal Q waves from pathological ones:

• A QS complex in lead V1 is normal 2
• Q wave < 25% of the R wave amplitude in lead III is normal if the frontal QRS axis is between 30° and 0° 2
• Q wave may be normal in aVL if the frontal QRS axis is between 60° and 90° 2
• Septal Q waves (small, non-pathological Q waves < 0.03 sec and < 25% of the R-wave amplitude) in leads I, aVL, aVF, and V4–V6 are normal 2

Clinical Significance and Evaluation

Pathological Q waves have significant clinical implications:

• They are reported in approximately 1-2% of all athletes, with higher prevalence in males and Black athletes 2
• Q waves are pathognomonic of prior myocardial infarction in patients with ischemic heart disease, regardless of symptoms 2
• The specificity of ECG diagnosis for MI is greatest when Q waves occur in several leads or lead groupings 2
• When Q waves are associated with ST deviations or T wave changes in the same leads, the likelihood of MI is increased 2

Location-Specific Considerations

The diagnostic value of Q waves varies by location:

• Anterior Q waves (V1-V4) reliably predict MI location, size, and transmural extent 3
• Inferior Q waves (II, III, aVF) are less reliable predictors of MI size in corresponding territories 3
• Lateral Q waves (V5, V6, I, aVL) are weak predictors of MI size 3
• A tall and broad R wave in V1-V2 is a more powerful predictor of lateral MI than Q waves 3

Common Pitfalls and Confounders

Several conditions can mimic pathological Q waves:

• Pre-excitation
• Obstructive, dilated or stress cardiomyopathy
• Cardiac amyloidosis
• Left bundle branch block
• Left anterior hemiblock
• Left ventricular hypertrophy
• Right ventricular hypertrophy
• Myocarditis
• Acute cor pulmonale
• Hyperkalemia 2

Evaluation Algorithm for Borderline Q Waves

When borderline Q waves are detected:

1. Perform echocardiography as the minimum evaluation to investigate for underlying cardiomyopathy 1
2. If echocardiogram is normal but clinical suspicion remains, consider cardiac MRI 1
3. For patients ≥30 years with risk factors for CAD, consider stress testing 1
4. In adolescents <16 years, consider that borderline Q waves in anterior leads may represent a normal "juvenile pattern" 1
5. In Black athletes, consider that borderline Q waves in anterior leads may be a normal variant, especially when associated with J-point elevation and convex ST-segment elevation 1

Prognostic Implications

The presence of pathological Q waves has important prognostic implications:

• Patients with Q waves on admission ECG show significantly larger infarct size and lower ejection fraction 4, 5
• Q waves are associated with more severe microvascular injury after myocardial infarction 5
• Q-wave regression is associated with larger improvement of left ventricular ejection fraction 4