From the Guidelines
The EKG pattern for Left Anterior Fascicular Block (LAFB) is characterized by a QRS duration <120 ms, a frontal plane axis between −45° and −90°, a qR pattern in lead aVL, an R-peak time in lead aVL of ≥45 ms, and an rS pattern in leads II, III, and aVF.
Key Characteristics
- QRS duration: <120 ms 1
- Frontal plane axis: between −45° and −90° 1
- Lead aVL pattern: qR (small r, tall R) 1
- R-peak time in lead aVL: ≥45 ms 1
- Leads II, III, and aVF pattern: rS (small r, deep S) 1
Diagnosis
LAFB is diagnosed based on the presence of these characteristic EKG findings, which indicate a block in the left anterior fascicle of the left bundle branch 1.
Clinical Significance
LAFB can be associated with various cardiac conditions, including hypertension, coronary artery disease, and cardiomyopathy 1.
From the Research
Left Anterior Fascicular Block (LAFB) EKG Pattern
The EKG pattern for Left Anterior Fascicular Block (LAFB) is characterized by:
- Marked left axis deviation (LAD) of -30 degrees or greater 2
- Delayed inscription of the intrinsicoid deflection (ID) in lead aVL asynchronous to V6 2
- Anterior Q waves in the V leads (V2 or V3) may be present, but are not indicative of myocardial infarction (MI) 3
- QRS duration may be prolonged, with a mean duration of 160 ms 4
- QT interval may be normal, with a mean duration of 400 ms 4
EKG Criteria for LAFB
The EKG criteria for LAFB include:
- Left axis deviation (LAD) of -30 degrees or greater 2
- Delayed inscription of the intrinsicoid deflection (ID) in lead aVL asynchronous to V6 2
- Presence of Q waves in the V leads (V2 or V3) with a duration of approximately 0.02 s and restricted to one or two leads 3
- Absence of S wave in lead I, or a very small S wave, in the presence of right bundle branch block (RBBB) and LAFB 4
Differential Diagnosis
LAFB can be mistaken for left bundle branch block (LBBB) due to similar EKG patterns 4
- RBBB with LAFB can imitate LBBB in the limb leads (absence of S wave in lead I) or in the precordial leads (absence of S wave in leads V5 and V6) 4
- Phase analysis can help differentiate LAFB from other conditions, such as inferior infarction 5
- Computer simulations can also help investigate the underlying mechanism of LAFB and provide a potential reference for diagnosis 6