Brugada ECG vs Incomplete Right Bundle Branch Block (iRBBB)

Why this differentiation matters

Brugada pattern is a malignant channelopathy associated with sudden cardiac death, while incomplete RBBB is usually a benign conduction variant. Mislabeling Brugada as iRBBB can be fatal; overcalling iRBBB as Brugada can lead to unnecessary anxiety and ICD implantation.

---

1. Basic Definitions

Brugada ECG Pattern

Primary repolarization abnormality

Genetic sodium-channel disorder

Characteristic ST-segment elevation in V1–V3

Risk of ventricular fibrillation and sudden death

Incomplete RBBB (iRBBB)

Depolarization abnormality

Delay in right ventricular conduction

Common in healthy individuals

Usually asymptomatic and benign

---

2. ECG Morphology: Side-by-Side Comparison

QRS Duration

Brugada: QRS usually <120 ms

iRBBB: QRS <120 ms, but with RBBB morphology

---

V1–V2 Pattern (Key Differentiator)

Brugada

Pseudo-RBBB appearance

ST elevation ≥2 mm

ST segment is coved or saddleback

Terminal QRS blends into ST segment

r′ is broad, rounded, and slow

iRBBB

Classic rSr′ pattern

r′ is sharp and narrow

ST segment is isoelectric or minimal elevation

Clear separation between QRS and ST segment

---

ST-Segment Shape

Feature Brugada iRBBB

ST elevation Present (≥2 mm) Absent or minimal

Shape Coved / Saddleback Flat

J-point Elevated Normal

---

T-Wave Orientation

Brugada: T-wave inverted in V1–V2 (Type 1)

iRBBB: T-wave usually upright or mildly discordant

---

3. Brugada ECG Types (Only Type 1 is Diagnostic)

Type 1 (Diagnostic)

Coved ST elevation ≥2 mm

Downsloping ST

Inverted T-wave

Type 2

Saddleback ST elevation

r′ present

Not diagnostic alone

Type 3

Minimal ST elevation (<2 mm)

Non-diagnostic

---

4. Response to High Right Precordial Leads

Brugada

ST elevation increases when V1–V2 placed in 2nd–3rd intercostal space

iRBBB

No significant change with lead repositioning

---

5. Pharmacological Challenge (Specialist Setting)

Sodium channel blockers (ajmaline, flecainide, procainamide)

Brugada

Converts Type 2/3 → Type 1

iRBBB

No Brugada pattern unmasked

---

6. Clinical Context (Critical Clues)

Feature Brugada iRBBB

Syncope Common Rare

Sudden cardiac death Yes No

Family history of SCD Often present Absent

Fever-induced changes Yes No

---

7. Common Pitfalls

Calling pseudo-RBBB + ST elevation as iRBBB

Ignoring ST morphology and focusing only on rSr′

Failure to record high intercostal V1–V2 leads

Misinterpreting athletic or young adult ECGs

---

8. Practical Bedside Rule

If V1–V2 show r′ + ST elevation → think Brugada first, not iRBBB.

iRBBB should never have significant ST elevation.

---

9. Summary Table

Feature Brugada iRBBB

Pathophysiology Repolarization Depolarization

ST elevation Present Absent

ST shape Coved / Saddleback Flat

r′ morphology Broad, slow Sharp, narrow

Risk Sudden death Benign

Management Risk stratification ± ICD Reassurance

---

Take-Home Message

Incomplete RBBB is a conduction delay, Brugada is a lethal electrical disease. The ST segment, not the rSr′, is the key. When in doubt, treat the ECG as Brugada until proven otherwise.