What is the clinical significance and appropriate management of an RS wave ratio of 1:1 in leads V5 and V6 on an ECG in the context of right bundle branch block (RBBB)?

RS Wave Ratio 1:1 in V5 and V6: Clinical Significance and Management

An RS wave ratio of 1:1 in leads V5 and V6 is abnormal and suggests right ventricular hypertrophy or pulmonary hypertension rather than right bundle branch block, as RBBB characteristically shows normal R peak time in V5 and V6 with a dominant R wave (not equal R and S waves). 1

Understanding the Normal Pattern vs. Pathologic Finding

In the context of RBBB, leads V5 and V6 should demonstrate:

• Normal R peak time (not prolonged) 1
• Dominant R waves with small S waves - specifically, the S wave should be of greater duration than the R wave or >40 ms in leads I and V6 for RBBB diagnosis 1
• An RS ratio of 1:1 (equal R and S waves) violates these criteria and indicates a different pathologic process 1

Differential Diagnosis for RS Ratio 1:1 in V5-V6

Primary Consideration: Right Ventricular Hypertrophy/Pulmonary Hypertension

The most likely diagnosis is right ventricular hypertrophy, particularly from pulmonary arterial hypertension, which characteristically produces:

• Large S wave and small R wave with R/S ratio ≤1 in lead V5 or V6 1
• Right axis deviation (present in 79% of pulmonary hypertension patients) 1
• Tall R wave in V1 with R/S ratio ≥1 1
• S1, S2, S3 pattern 1

This pattern reflects the electrical dominance of the hypertrophied right ventricle extending into the lateral precordial leads 1.

Alternative Considerations

• Posterior myocardial infarction - can produce tall R waves in V1-V2 but typically shows dominant R waves (not equal RS) in V5-V6 2
• Misplaced precordial leads - must be excluded by verifying proper electrode placement 3
• Dextrocardia - would show progressive decrease in R wave amplitude from V1 to V6 2

Diagnostic Algorithm

Step 1: Verify Technical Accuracy

• Confirm correct lead placement, particularly that V5 and V6 are at the 5th intercostal space at anterior and mid-axillary lines 3
• Repeat ECG if placement is uncertain 4

Step 2: Assess QRS Duration and Morphology

• Measure QRS duration: If ≥120 ms with RSR' in V1-V2, RBBB is present but the RS ratio 1:1 in V5-V6 indicates concurrent right ventricular hypertrophy 1
• Examine V1-V2: Look for tall R wave with R/S ≥1, which supports RVH 1
• Check axis: Right axis deviation ≥100° strongly suggests RVH/pulmonary hypertension 1

Step 3: Evaluate for Pulmonary Hypertension

Given the high specificity of this finding for RVH, immediate echocardiography is mandatory to:

• Assess right ventricular size and function 1
• Estimate pulmonary artery systolic pressure 1
• Evaluate for structural heart disease 4

Step 4: Additional Diagnostic Testing

• Chest radiography to assess for cardiomegaly and pulmonary vascular changes 1
• Brain natriuretic peptide (BNP) if right heart failure is suspected 1
• Consider right heart catheterization if echocardiography suggests pulmonary hypertension (mean PA pressure >20 mmHg) 1

Management Approach

Immediate Actions

• Obtain comprehensive history focusing on:

  • Dyspnea, particularly with exertion 1
  • Syncope or presyncope (ominous signs) 1, 4
  • Risk factors for pulmonary hypertension (connective tissue disease, congenital heart disease, chronic thromboembolic disease, sleep apnea) 1

• Physical examination should specifically assess for:

  • Loud P2 component of second heart sound (93% sensitive for pulmonary hypertension) 1
  • Right ventricular heave 1
  • Jugular venous distension, hepatomegaly, peripheral edema (indicating right heart failure) 1
  • Low blood pressure and cool extremities (markedly reduced cardiac output - ominous finding) 1

Risk Stratification

Prognostic ECG features that indicate higher mortality risk:

• P-wave amplitude in lead II ≥0.25 mV (2.8-fold increased death risk) 1
• Each additional 1 mm P-wave amplitude in lead III (4.5-fold increased death risk) 1

Treatment Considerations

• If pulmonary hypertension is confirmed, refer urgently to pulmonary hypertension specialist for disease-specific therapy 1
• If RBBB coexists with RVH, monitor for progression to higher-degree conduction disorders 1, 4
• Symptomatic patients with syncope require electrophysiology consultation to exclude high-grade AV block 4, 3

Critical Pitfalls to Avoid

1. Do not dismiss this as "just RBBB" - the RS ratio 1:1 in V5-V6 indicates additional pathology beyond simple conduction delay 1

2. Do not delay echocardiography - this ECG pattern has 87% sensitivity for right ventricular hypertrophy in pulmonary hypertension patients 1

3. Recognize that normal ECG does not exclude pulmonary hypertension - 8 of 61 patients with severe PAH (mean PA pressure 50 mmHg) had normal ECGs, but an abnormal pattern like RS 1:1 in V5-V6 is highly specific 1

4. Consider acute pulmonary embolism - particularly if acute presentation with hemodynamic instability; a QR pattern in V1 with RBBB has high positive predictive value for massive PE causing cardiac arrest 5