Left anterior fascicular block (LAFB)
Also calledLAFB · left anterior fascicular block · left anterior hemiblock · LAHB
Definition
Conduction delay in the left anterior fascicle of the left bundle branch, which shifts the main direction of left ventricular activation upward and to the left. Diagnosed by marked left axis deviation (frontal QRS axis -45 to -90 degrees), a qR complex in aVL with an R-peak time of 45 ms or more, an rS pattern in leads II, III and aVF (with the S wave deeper in III than in II), and a QRS duration under 120 ms.
Sources
- Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances. Circulation. 2009;119(10):e235-e240. doi.org/10.1161/CIRCULATIONAHA.108.191095
- Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382-e482. doi.org/10.1161/CIR.0000000000000628
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.