Bundle Branch Block

Conduction abnormality in the His–Purkinje system characterized by delayed or blocked electrical impulse propagation through either the right (RBBB) or left bundle branch (LBBB)

Right Bundle Branch Block

ECG features:
  • QRS ≥120 ms
  • rSR' "M-shaped" pattern in V1–V3
  • Wide S-wave in leads I and V6
  • ST depression/T inversion in right chest leads
Mnemonic: "Rabbit ears in V1"

Left Bundle Branch Block

ECG features:
  • QRS ≥120 ms
  • Broad, notched R-wave in leads I, V5, V6
  • Deep S-wave in V1
  • Absence of Q-waves in lateral leads
  • Discordant ST-T segment changes
Mnemonic: "WiLLiaM – Wi in V1 (W pattern), LL in V6 (M pattern)"
 
notion image