Expansion
WiLLiaM MaRRoW: left gives W in V1 and M in V6; right gives M in V1 and W in V6
Expansion
Both require a QRS duration of 120 ms or more.
WiLLiaM - Left bundle branch block
- W shape in V1
- M shape in V6
MaRRoW - Right bundle branch block
- M shape in V1
- W shape in V6
In right bundle branch block the right ventricle depolarises late, through slow muscle-to-muscle spread, giving the terminal R prime in V1 and a slurred S in V6. It is often benign and can occur in healthy people.
Left bundle branch block is more significant: it reverses the normal direction of septal depolarisation, makes the ECG uninterpretable for ischaemia, and new left bundle branch block with chest pain is treated as an acute coronary occlusion.