Right Bundle Branch Block (RBBB)

ECG Diagnostic Criteria

• QRS duration greater than 120ms
• RSR pattern in V1-3 (M-shaped QRS complex)
• Wide, slurred S wave in lateral leads (I, aVL, V5-6)

Key Features of RBBB

• V1: RSR pattern, with discordant T wave changes
• V6: Widened, slurred S wave
• Associated Features: Appropriate discordance with ST depression/T-wave inversion in right precordial leads (V1-3)

Electrophysiology of RBBB

• Normal cardiac conduction involves equal impulse travel down right and left bundles
• In RBBB, left ventricle activates normally, with unchanged septal depolarisation
• Delayed right ventricle activation originates across the septum
  • Results in a secondary R wave (R) in precordial leads and wide, slurred S waves in lateral leads
• Normal cardiac axis in isolated RBBB

Sequence of Conduction in RBBB

1. Normal left ventricular activation via left bundle
2. Unaffected septal depolarisation for a normal early QRS complex
3. Right ventricle activation across septum causing delayed R waves in V1-3 and S waves in lateral leads

ECG QRS Morphology

QRS Morphology in V1

• Sometimes shows a broad monophasic R wave or a qR complex instead of RSR pattern

QRS Morphology in Lateral Leads

• Wide slurred S wave in lead I

Appropriate Discordance

• Abnormal depolarisation followed by abnormal repolarisation, discordant to preceding QRS complex
• In RBBB, seen as ST depression and/or T-wave inversion in V1-3

Causes of Right Bundle Branch Block

• Right ventricular hypertrophy/cor pulmonale
• Pulmonary embolus
• Ischaemic heart disease
• Rheumatic heart disease
• Congenital heart disease (e.g., atrial septal defect)
• Myocarditis
• Cardiomyopathy
• Lengre-Lev disease (fibrosis of the conducting system)
• New RBBB in chest pain context is concerning for OMI, indicating potential reperfusion therapy

ECG Examples of Right Bundle Branch Block

Example 1: RBBB with LAFB

• Broad QRS > 120ms
• Delayed RV conduction with tall, broad R wave in V1
• Widened S wave in lead I
• Appropriate discordance in right precordial leads with T-wave inversion

Example 2: Isolated RBBB

• RSR pattern in V1-2
• Widened S waves in lateral leads, especially V4-6
• Appropriate discordance in V1-2

Example 3: Isolated RBBB

• RSR pattern in V1-3
• No lateral S wave changes
• Normal axis

Example 4: RBBB with LAFB in chest pain context

• RSR pattern in V1-3, slurred S waves laterally
• Concordant ST changes and hyper-acute T waves inferiority
• Indicates 99% proximal LAD occlusion

Incomplete RBBB

• Defined as RSR pattern in V1-3 with QRS duration < 120ms
• Common in children, of no clinical significance

Differential Diagnosis of RBBB

• Can be mimicked by Brugada syndrome and other conditions like LBBB, LAFB, LPFB, IVCD, bifascicular block, trifascicular block, and complete heart block

Further Reading and Resources

• Various online courses, textbooks, and additional resources are available for advanced ECG interpretation and understanding RBBB in detail
• Notable authors and resources include Ed Burns and Robert Buttner, who contribute extensively to ECG interpretation and education