Right bundle branch block (RBBB)

• QRS duration of 120 ms (3 small squares) or more
• Secondary R wave (R') in lead V1
• Other features:
• Slurring of S wave in the lateral leads V4-6, I, and AVL
• The T wave tends to be opposite of the terminal QRS component i.e. T wave inversion in the septal leads (V1-3) may be seen

Features of this ECG

• Sinus tachycardia, 114 b.p.m. normal QRS axis
• Diagnostic features of RBBB:
• Broad QRS, 145 ms
• Secondary R wave in V1, rSR' pattern

• Other features of RBBB:
• T wave inversion
• Slurred S wave

• Terminal negative component of P wave in lead V1
• Possible left atrial abnormality

Causes of right bundle branch block

• May occur in the absence of heart disease
• Fibrotic degeneration
• Ischaemic heart disease
• Hypertension
• Cardiomyopathy
• Congenital heart disease
• Atrial septal defect
• Fallot's tetralogy

• Acute, massive, pulmonary embolus