What is the significance of a deep S wave in lead V5 on a 12‑lead ECG and how should it be evaluated?

Deep S Waves in Lead V5: Clinical Significance and Evaluation

A deep S wave in lead V5 is an abnormal ECG finding that most commonly indicates right ventricular hypertrophy, pulmonary hypertension, or certain cardiomyopathies, and requires systematic evaluation to exclude underlying cardiopulmonary disease.

Diagnostic Significance

Right Ventricular Hypertrophy and Pulmonary Hypertension

• A deep S wave in V5 is a specific marker for right ventricular hypertrophy and pulmonary hypertension, with an S-wave depth ≥0.42 mV (4.2 mm) serving as a clinically useful cut-off for screening pulmonary hypertension 1
• The Sokolow-Lyon voltage criteria for RV hypertrophy (R in V1 + S in V5 or V6 >10.5 mm) incorporate the deep S wave in V5 as a key diagnostic component 2
• In patients with suspected pulmonary hypertension, S-wave depth in V5 was an independent predictor of mean pulmonary arterial pressure ≥25 mmHg (odds ratio 1.25 per mm increase) 1

Complete Right Bundle Branch Block

• In complete RBBB, the S wave in V5 or V6 should be of greater duration than the R wave or exceed 40 ms in adults, representing delayed right ventricular activation 2
• The presence of a deep S wave in V5 with duration >40 ms, combined with an rsR' pattern in V1 and QRS duration ≥120 ms, confirms complete RBBB 2

Cardiomyopathy Patterns

• In arrhythmogenic left ventricular cardiomyopathy (ALVC), a sum of S-wave in V1 plus R-wave in V6 ≤12 mm effectively discriminates ALVC patients from healthy controls (AUC 0.784), though this focuses on V6 rather than V5 specifically 3
• Low total 12-lead QRS voltage (including diminished S waves in lateral leads) may paradoxically indicate infiltrative cardiomyopathies such as cardiac sarcoidosis or amyloidosis, where mean total voltage is approximately 104-117 mm despite increased heart weight 4

Evaluation Algorithm

Initial Assessment

1. Measure the exact S-wave depth in V5 – A depth ≥4.2 mm (0.42 mV) raises concern for pulmonary hypertension 1
2. Calculate Sokolow-Lyon voltage – R in V1 + S in V5 (or V6); >10.5 mm suggests RV hypertrophy 2
3. Assess QRS duration and morphology – Determine if complete RBBB is present (QRS ≥120 ms with rsR' in V1 and S duration >40 ms in V5) 2
4. Examine for right axis deviation – Right axis deviation combined with deep S in V5 strengthens the diagnosis of RV hypertrophy 2

Diagnostic Work-Up

• Transthoracic echocardiography is mandatory to assess right ventricular size and function, estimate pulmonary artery systolic pressure, evaluate for RV hypertrophy, and exclude congenital heart disease 2
• Right heart catheterization should be performed when echocardiography suggests pulmonary hypertension (estimated PASP >35-40 mmHg) to confirm the diagnosis and measure mean pulmonary arterial pressure directly 1
• Cardiac MRI may be indicated if echocardiography is non-diagnostic or if arrhythmogenic cardiomyopathy is suspected based on additional ECG features (T-wave inversions, low voltage, pathological Q waves) 3
• Exercise testing and 24-hour ECG monitoring are recommended when bundle branch block is identified to evaluate for underlying pathological causes and assess for arrhythmias 2

Differential Diagnosis by Clinical Context

High-Risk Patterns Requiring Urgent Evaluation

• Deep S in V5 (≥4.2 mm) + T-wave inversions in precordial leads extending to V4 – This pattern strongly suggests significant pulmonary hypertension and warrants urgent echocardiography and consideration of right heart catheterization 1
• Deep S in V5 + right axis deviation + right atrial enlargement – This triad indicates advanced RV pressure or volume overload from pulmonary hypertension, pulmonary stenosis, or congenital heart disease 2

Intermediate-Risk Patterns

• Deep S in V5 as part of complete RBBB (QRS ≥120 ms) – While RBBB can be idiopathic in the right bundle, it may represent early manifestations of ischemic heart disease, cardiomyopathy, or progressive conduction disease (Lenegre disease) and requires comprehensive evaluation 2
• Deep S in V5 with low total QRS voltage (<120 mm) – This paradoxical combination suggests infiltrative cardiomyopathy (sarcoidosis, amyloidosis) rather than hypertrophy 4

Athletic Population Considerations

• Isolated voltage criteria for RV hypertrophy (including deep S in V5) are uncommon in athletes (<2% prevalence) and should not be attributed to physiological adaptation without excluding underlying cardiovascular disease 2
• The presence of RV hypertrophy criteria in an athlete mandates cardiological work-up including exercise testing, 24-hour ECG, and imaging 2

Common Pitfalls and Caveats

• Do not dismiss deep S waves in V5 as a normal variant – Unlike isolated increased QRS voltage for left ventricular hypertrophy (common in athletes), RV hypertrophy patterns are uncommon in healthy individuals and warrant investigation 2
• Recognize that electrode misplacement can create pseudo-pathological patterns – Verify proper V5 placement (fifth intercostal space, anterior axillary line) before proceeding with extensive work-up 2
• Avoid comparing standard 12-lead ECGs with derived or reduced-lead systems – Serial ECG changes should be assessed using one consistent method, as S-wave amplitude may vary between systems 5
• Consider age-specific normal variants – In children and adolescents, RV dominance with deeper S waves in left precordial leads may be physiological, but this pattern should normalize by late adolescence 2

Prognostic Implications

• The depth of the S wave in V5 correlates with the severity of pulmonary hypertension – Each 1 mm increase in S-wave depth increases the odds of significant PH by 25% 1
• Complete RBBB with deep S waves in V5 carries increased risk – Combinations of bundle branch block and hemiblock reflect extensive conduction system involvement and increase the risk of clinically significant AV block 2
• When deep S in V5 occurs with other low-voltage findings, suspect infiltrative disease – Cardiac sarcoidosis severe enough to warrant heart transplantation typically presents with paradoxically low total QRS voltage (mean 90-117 mm) despite increased heart weight 4