What is the significance of a small R wave and deep S wave in leads II (second lead) and aVF (augmented voltage unipolar left foot lead) in an adult patient with potential risk factors for coronary artery disease (CAD), with all other electrocardiogram (ECG) leads appearing normal, and could it indicate left anterior descending (LAD) artery disease?

ECG Pattern of Small R Wave and Deep S Wave in Leads II and aVF

The pattern you describe—small r wave and deep S wave (rS pattern) in leads II and aVF—is the classic ECG finding of left anterior fascicular block (LAFB), not left anterior descending (LAD) coronary artery disease. This is a conduction abnormality, not an ischemic pattern. 1

Understanding the ECG Pattern

Left Anterior Fascicular Block Criteria

According to the ACC/AHA/HRS guidelines, left anterior fascicular block is diagnosed when: 1

• QRS duration remains <120 ms (normal duration)
• Frontal plane axis between -45° and -90° (left axis deviation)
• qR pattern in lead aVL (small q, tall R)
• rS pattern in leads II, III, and aVF (small r, deep S) - exactly what you're describing
• R-peak time in lead aVL ≥45 ms

This is a benign conduction abnormality in most cases and does not indicate coronary artery disease. 1

Why This Is NOT LAD Disease

Key Distinctions

The confusion likely stems from the abbreviation "LAD," but these are completely different entities:

• LAFB = Left Anterior Fascicular Block (conduction system disease)
• LAD = Left Anterior Descending artery (coronary artery)

LAD coronary artery disease produces entirely different ECG patterns: 1

• ST-segment elevation or depression in anterior leads (V1-V4)
• Deep symmetrical T-wave inversions ≥2 mm in precordial leads
• Pathological Q waves (≥0.03 sec duration and ≥0.1 mV deep) in anterior leads
• Loss of R wave progression or reversed R wave progression in precordial leads

What LAD Disease Actually Looks Like

Critical LAD stenosis typically manifests as: 2, 3

• Marked symmetrical T-wave inversion ≥2 mm in multiple precordial leads (V1-V4)
• Reversed R wave progression (RV2 < RV1, RV3 < RV2, or RV4 < RV3)
• ST-segment changes in anterior/anterolateral leads
• Associated anterior wall motion abnormalities on imaging

Your pattern (rS in inferior leads II and aVF with normal other leads) does not fit any ischemic pattern. 1

Clinical Significance of Your ECG Finding

When LAFB Is Benign

Left anterior fascicular block alone in an asymptomatic patient with normal other leads is generally benign and requires no specific treatment. 1

Common benign scenarios include:

• Isolated finding in elderly patients
• Associated with hypertension or left ventricular hypertrophy
• Chronic stable finding on serial ECGs

When Further Evaluation Is Needed

Consider additional workup if: 1

• New onset compared to prior ECGs (suggests acute process)
• Associated symptoms (chest pain, dyspnea, syncope)
• Progression to bifascicular block (LAFB + right bundle branch block)
• Other ECG abnormalities beyond the isolated LAFB pattern
• Clinical context suggesting structural heart disease

Common Pitfalls to Avoid

Misinterpretation Errors

Do not confuse the rS pattern in inferior leads (II, III, aVF) with ischemia. 1 This is the expected pattern in LAFB due to altered ventricular activation sequence, not myocardial injury.

The absence of other concerning features (ST changes, T-wave inversions, Q waves, or R wave progression abnormalities) strongly argues against acute coronary syndrome. 1

What to Actually Look For

If concerned about LAD disease, specifically assess: 1, 2

• Precordial leads V1-V4 for ST changes or T-wave inversions
• R wave progression from V1 to V6 (should increase normally)
• Presence of pathological Q waves in anterior leads
• Comparison with prior ECGs to identify new changes

Practical Recommendation

If all other ECG leads are truly normal (normal R wave progression, no ST changes, no T-wave inversions, no pathological Q waves), and you only have the rS pattern in leads II and aVF, this represents isolated left anterior fascicular block—a conduction abnormality, not coronary artery disease. 1

No specific cardiac workup is needed for isolated LAFB in an asymptomatic patient. 1 However, if this is a new finding or the patient has cardiac symptoms or risk factors, basic evaluation with echocardiography to assess for structural heart disease may be reasonable. 1

The key message: This ECG pattern does not indicate LAD coronary artery disease. 1