bundle branch block
LBBB (the classic "William")
formal criteria
- QRS duration ≥ 120ms
- Dominant S wave in V1
- Broad monophasic R wave in lateral leads (I, aVL, V5-6)
- Absence of Q waves in lateral leads
- Prolonged R wave peak time > 60ms in leads V5-6
Source: LITFL
causes
- Anterior MI
- ischaemic heart disease
- hypertension
- aortic stenosis
- cardiomyopathy
- rare: idiopathic fibrosis, digoxin toxicity, hyperkalaemia
In patients with LBBB, you can't look for ST changes - use Sgarbossa criteria instead
https://litfl.com/sgarbossa-criteria-ecg-library/
RBBB
Source: LITFL
causes
- Massive pulmonary embolism
- Myocarditis
- RVH
- ischaemic heart disease