From the Guidelines
Left anterior fascicular block (LAFB) on an electrocardiogram (ECG) is diagnosed based on specific criteria, including a frontal plane axis between 45° and 90°, a qR pattern in lead aVL, an R-peak time in lead aVL of 45 ms or more, and a QRS duration less than 120 ms, as outlined in the 2009 AHA/ACCF/HRS recommendations 1. When evaluating an ECG for LAFB, it is essential to consider these criteria to ensure accurate diagnosis. The presence of LAFB may indicate underlying cardiac conditions, and thus, a thorough cardiac evaluation is necessary. This evaluation should include:
- Assessment of symptoms
- Physical examination
- Possibly additional cardiac testing, depending on the clinical context
- Regular follow-up ECGs to monitor for progression of conduction disease It is crucial to note that LAFB may not require specific treatment on its own but can be a marker of underlying cardiac disease, such as coronary artery disease, hypertensive heart disease, or cardiomyopathy. Furthermore, when LAFB occurs with right bundle branch block, it represents bifascicular block, which carries a higher risk of progression to complete heart block, as stated in the guidelines 1. Therefore, careful consideration and monitoring of patients with LAFB are necessary to prevent potential complications.
From the Research
Left Anterior Fascicular Block EKG
- Left anterior fascicular block (LAFB) is a heart condition that can be identified by an abnormal electrocardiogram (ECG) 2, 3.
- The ECG criteria for LAFB include marked left axis deviation (LAD) and a delay in the time of inscription of the intrinsicoid deflection (ID) in lead aVL asynchronous to V6 2.
- However, the lack of correlation between these criteria in many instances questions their validity, and LAD alone should not be considered synonymous with LAFB 2.
- Recognition of delayed inscription of the ID in aVL is a useful supplemental criterion for diagnosis 2.
- LAFB has been associated with an increased risk of heart failure, and non-specific intraventricular conduction delay due to lesions of the conduction bundles and slow cell-to-cell conduction has also been considered as another cause of heart failure 3.
- Simulation studies have shown that typical LAFB ECG patterns can also be observed from cases with slowed conduction velocity in the ventricular myocardium, with main differences in the duration of QRS and wave amplitude 3.
ECG Patterns and Diagnosis
- LAFB decreases the voltage in the chest leads and increases the voltage in the limb leads, and the usual voltage criteria of left ventricular hypertrophy must be modified appropriately 4.
- Changes in repolarization include a decrease in the T wave of leads I and AVL and an increase in leads II, III, AVF, V5, and V6 4.
- Small Q waves in V2 may simulate an anteroseptal myocardial infarction, and both inferior and anterior myocardial infarctions may be masked by R waves replacing Q waves 4.
- LAFB may mask or mimic infarction and left ventricular hypertrophy and mask right bundle branch block in the setting of an acute anterior myocardial infarction 4.
Prognostic Significance
- LAFB has been found to be an independent risk factor for all-cause death and cardiac death, with a higher incidence of pathological coronary artery disease (CAD) and myocardial infarction (MI) in LAFB patients 5.
- LAFB patients have heavier hearts, thicker left ventricular walls, and suffer increased risk of death and cardiac death, with the major cause of death being cardiac death, including more MI, myocarditis, and cardiac rupture 5.