QRS duration ≥ 120ms
V1: Dominant S wave
V6: broad, notched (‘M’-shaped) R wave
LBBB causes:
- Aortic stenosis
- Ischaemic heart disease / AMI
- Hypertension
- Valvular disorders
- Dilated cardiomyopathy
- Hyperkalaemia
- Digoxin toxicity
- Sometimes an incidental finding in the older patient
LBBB remains an indication for angiography, although you will have to convince the cardiologist that it is new and due to an infarct.
EBM:
Margarida Pujol-López et al. Left Bundle Branch Block: Characterization, Definitions, and Recent Insights into Conduction System Physiology. Cardiol Clin. 2023 Aug;41(3):379-391. Left bundle branch block (LBBB) is not just a simple electrocardiogram alteration. The intricacies of this general terminology go beyond simple conduction block. This review puts together current knowledge on the historical concept of LBBB, clinical significance, and recent insights into the pathophysiology of human LBBB.