What does a notched Q (quantum) wave in lead II on an electrocardiogram (ECG) indicate?

Notched Q Wave in Lead II on ECG: Clinical Significance and Interpretation

A notched Q wave in lead II on an electrocardiogram (ECG) most commonly suggests prior inferior wall myocardial infarction, but can also represent a normal variant depending on specific characteristics and clinical context. Careful evaluation of the Q wave's width, depth, and associated ECG findings is essential for accurate interpretation.

Characteristics of Pathological vs. Normal Q Waves

Pathological Q Waves

• Q wave ≥0.03 seconds in duration and ≥0.1 mV deep in lead II suggests prior myocardial infarction 1
• Increased specificity when Q waves appear in multiple contiguous leads (II, III, aVF) 1
• Often associated with other ECG abnormalities like T-wave inversion in the same lead group 1
• More likely to be pathological when accompanied by regional wall motion abnormalities on imaging

Normal Q Wave Variants

• Small, non-pathological septal Q waves (<0.03 sec and <25% of R-wave amplitude) can appear in leads I, aVL, aVF, and V4–V6 1
• A Q wave <0.03 sec and <25% of R-wave amplitude in lead III is normal if the frontal QRS axis is between 30° and 0° 1
• Q waves in inferior leads may be positional and not necessarily indicative of disease 2

Clinical Significance of Q Waves in Lead II

Myocardial Infarction

• Q waves in lead II, particularly when present in other inferior leads (III, aVF), typically indicate inferior wall myocardial infarction 3
• When Q waves appear in inferior leads, approximately 59% of the scar tissue involves the inferior and inferoseptal walls 3
• Early Q waves (appearing <6 hours from symptom onset) in inferior MI have different prognostic implications than those in anterior MI 4

Non-Ischemic Causes

The American College of Cardiology recognizes several non-ischemic causes of Q waves 5:

• Cardiomyopathies (hypertrophic, dilated, stress, cardiac amyloidosis)
• Conduction abnormalities (LBBB, left anterior hemiblock)
• Pre-excitation syndromes
• Ventricular hypertrophy
• Myocarditis
• Acute cor pulmonale
• Hyperkalemia

Evaluation Algorithm for Notched Q Wave in Lead II

1. Assess Q wave characteristics:

   • Measure duration (≥0.03 sec is concerning)
   • Measure depth (≥0.1 mV or ≥25% of R-wave amplitude is concerning)
   • Note presence of notching (may indicate more extensive damage)

2. Examine other leads:

   • Check for Q waves in contiguous leads (III, aVF)
   • Look for associated ST-T wave changes

3. Review clinical context:

   • History of chest pain or equivalent symptoms
   • Cardiovascular risk factors
   • Prior ECGs for comparison (essential)

4. Perform imaging:

   • Echocardiography to assess wall motion abnormalities
   • Consider cardiac MRI if echocardiogram is normal but clinical suspicion remains high 5

Important Caveats and Pitfalls

• Respiratory variation: Unlike previously thought, respiratory variation (persistence of Q waves during deep inspiration) is unreliable for differentiating normal from abnormal Q waves in inferior leads 6

• Prognostic implications: New Q waves on presenting ECG in acute MI are independently associated with worse outcomes, including lower ejection fraction and increased cardiac mortality 7

• Lead misplacement: Improper lead placement can create false Q waves, emphasizing the importance of proper technique 5

• Isolated finding: A notched Q wave in lead II alone, without other ECG or clinical abnormalities, is less specific for pathology than when accompanied by other findings

• Clinical correlation: The American College of Cardiology emphasizes that correct evaluation of Q waves requires integration of clinical data, not just ECG findings 5

Remember that while Q waves often indicate prior myocardial infarction, their interpretation must always be made in the appropriate clinical context with consideration of patient demographics, symptoms, and additional diagnostic testing.