Diagnostic Criteria for Left Bundle Branch Block and Left Anterior Fascicular Block

Left Bundle Branch Block (LBBB) Criteria

The American Heart Association recommends that the presence of a broad notched or slurred R wave in lead aVL is one of the defining criteria for complete LBBB, with a QRS duration ≥120 ms in adults 1, 2
The American College of Cardiology suggests that LBBB criteria include a broad notched or slurred R wave in leads I, aVL, V5, and V6, with absent Q waves in leads I, V5, and V6 1, 2
The LBBB criteria also include an R peak time >60 ms in leads V5 and V6, according to the American Heart Association 1, 2

The American Heart Association states that a qR pattern in lead aVL is the hallmark morphology for LAFB, with a frontal plane axis between −45° and −90° 1, 2
The American College of Cardiology recommends that the diagnostic criteria for LAFB include a qR pattern in lead aVL, with an R-peak time in lead aVL of ≥45 ms 1, 2
The LAFB criteria also include a QRS duration <120 ms and an rS pattern in leads II, III, and aVF, according to the American Heart Association 1, 2

The American Academy of Pediatrics notes that age-dependent normal values must be considered when evaluating conduction abnormalities, as QRS duration criteria differ significantly between adults and children 3