What is the significance of Q waves in leads V1 to V4 on an electrocardiogram (ECG) in patients with hypertrophic cardiomyopathy (HCM)?

Q Waves in V1-V4 in Hypertrophic Cardiomyopathy: Diagnostic Significance

Q waves in leads V1-V4 in patients with hypertrophic cardiomyopathy (HCM) are associated with areas of myocardial fibrosis and represent an asymmetrical distribution of left ventricular hypertrophy. 1

Pathophysiological Basis of Q Waves in HCM

Q waves in HCM have a different pathophysiological basis than those seen in myocardial infarction:

• Myocardial Fibrosis: Q waves in HCM correlate with the presence, segmental extent, and transmural extent of myocardial fibrosis as demonstrated by late gadolinium enhancement (LGE) on cardiac MRI 2

• Asymmetrical Hypertrophy: Abnormally deep Q waves in the anterior leads (V1-V4) are typically associated with asymmetrical distribution of left ventricular hypertrophy 1

• Septal Hypertrophy: The ratio of septal to posterior wall thickness is significantly higher in HCM patients with Q waves compared to those without (2.3 vs. 1.6) 2

Diagnostic Criteria and Significance

The European Society of Cardiology guidelines define pathological Q waves in HCM as:

• Q wave ≥40 ms in duration and/or
• ≥25% of the R wave in depth and/or
• ≥3 mm in depth in at least two contiguous leads 1

These Q waves have important diagnostic and prognostic implications:

• Diagnostic Value: Marked repolarization abnormalities, conduction abnormalities, and Q waves are unusual in hypertensive heart disease but common in HCM, making them valuable for differential diagnosis 1

• Prognostic Significance: Q waves are associated with greater extent of myocardial fibrosis, which is a substrate for ventricular arrhythmias and sudden cardiac death 3

Differentiation from Other Conditions

Q waves in HCM must be distinguished from those seen in:

1. Myocardial Infarction: In HCM, Q waves are usually associated with positive T waves, whereas in MI, T waves are often inverted in the same leads 1

2. Normal Variants: Septal Q waves can occur normally in leads I, aVL, aVF, and V4–V6 but are typically small and non-pathological 4

3. Hypertensive Heart Disease: While LVH by voltage criteria is seen in 10-20% of hypertensive patients with LVH, marked repolarization abnormalities, conduction abnormalities, and Q waves are unusual in hypertensive patients 1

Clinical Implications

The presence of Q waves in V1-V4 in HCM patients has several important clinical implications:

• Fibrosis Detection: Fragmented QRS (fQRS) and Q waves on ECG have high sensitivity (84.6%) and specificity (90.0%) for predicting myocardial fibrosis in HCM 3

• Risk Stratification: The extent of myocardial fibrosis correlates with arrhythmic risk and adverse outcomes 5

• Differential Diagnosis: Q waves help distinguish sarcomeric HCM from phenocopies such as cardiac amyloidosis, glycogen storage disease, or Fabry disease 5

Evaluation Approach

When Q waves are identified in V1-V4 in a patient with suspected HCM:

1. Comprehensive ECG Analysis: Look for other HCM-associated findings such as LVH by voltage criteria, T-wave inversions, and ST-segment abnormalities 1

2. Echocardiography: Assess for asymmetric septal hypertrophy, LV wall thickness, and distribution of hypertrophy 1

3. Cardiac MRI: Consider for definitive assessment of myocardial fibrosis through late gadolinium enhancement, particularly when echocardiography is inconclusive 4

4. Family Screening: Consider genetic testing and family screening, as HCM is often inherited in an autosomal dominant pattern 1

Conclusion

Q waves in V1-V4 in HCM patients represent an important ECG finding that correlates with myocardial fibrosis and asymmetrical distribution of left ventricular hypertrophy. Their presence should prompt thorough evaluation for HCM and risk stratification, as they may indicate more extensive disease and potentially higher risk for adverse outcomes.