What does a deep S wave on an electrocardiogram (ECG) indicate?

Deep S Wave on Electrocardiogram: Clinical Significance

A deep S wave on an electrocardiogram (ECG) can indicate several cardiac conditions including right ventricular hypertrophy, pulmonary hypertension, left ventricular hypertrophy, or may be a marker of underlying cardiomyopathy, requiring further evaluation with echocardiography and possibly cardiac MRI.

Physiological vs. Pathological Deep S Waves

Deep S waves can be seen in various clinical contexts:

Pathological Causes:

• Right Ventricular Overload: Deep S waves in leads I and V6 are significantly more common in patients with cardiopulmonary diseases causing right ventricular overload 1
• Pulmonary Hypertension: A deeper S wave in lead V5 (>0.42 mV) is an independent predictor of pulmonary hypertension 2
• Cardiomyopathy: Deep S waves may be associated with various cardiomyopathies 1
• Acute Myocardial Ischemia: During acute anterior transmural ischemia, S-wave amplitude typically decreases in precordial leads V1-V4 3

Normal Variants:

• Isolated deep S waves without other concerning findings may be normal variants
• Athletic heart remodeling may sometimes present with altered QRS morphology

Diagnostic Approach

When a deep S wave is identified on ECG:

1. Assess for associated ECG abnormalities:

   • Pathological Q waves (defined as Q/R ratio ≥0.25 or ≥40 ms in duration in two or more contiguous leads except III and aVR) 4
   • ST-segment depression (>0.05 mV in two or more leads) 4
   • T-wave inversions, especially if present in inferior or lateral leads 4
   • QRS prolongation or bundle branch blocks 4

2. Evaluate clinical context:

   • Presence of symptoms (chest pain, dyspnea, syncope)
   • Age and athletic status
   • Family history of cardiac disease or sudden cardiac death

3. Further cardiac evaluation:

   • Echocardiography is the minimum evaluation for patients with concerning ECG findings to investigate for underlying cardiomyopathy 4, 5
   • Cardiac MRI should be considered based on echocardiographic findings or clinical suspicion 4, 5

Special Considerations

Athletes

• Athletes with deep S waves and other concerning ECG findings require comprehensive evaluation, including echocardiography, CMR, 24-hour ECG monitoring, and exercise ECG testing 5
• The international recommendations for ECG interpretation in athletes emphasize the importance of distinguishing physiological adaptations from pathological findings 4

Bundle Branch Blocks

• Right bundle branch block reduces the amplitude of S waves in right precordial leads, which may affect the sensitivity of ECG criteria for left ventricular hypertrophy 4
• In left bundle branch block, specific criteria for diagnosing LVH include S V1 >2 mm and R V5/V6 >15 mm 4

Clinical Pitfalls to Avoid

1. Don't dismiss isolated deep S waves without considering clinical context

   • Even in asymptomatic individuals, deep S waves may be an early marker of underlying cardiac disease

2. Don't rely solely on ECG for definitive diagnosis

   • ECG findings should guide further investigation with imaging studies

3. Be aware of lead placement issues

   • Improper lead placement can affect S wave morphology and depth

4. Consider population-specific normal variants

   • Athletic remodeling may produce ECG changes that mimic pathology

Follow-up Recommendations

For patients with deep S waves and other concerning ECG findings:

• Referral to cardiology for further evaluation
• Regular follow-up with serial cardiac imaging including annual ECG and echocardiography 5
• Risk stratification for sudden cardiac death in those diagnosed with underlying cardiac pathology

Deep S waves, particularly when accompanied by other ECG abnormalities, warrant thorough investigation as they may represent an early sign of significant cardiac pathology that could impact morbidity and mortality.