From the Guidelines
Left anterior fascicular block (LAFB) is a cardiac conduction abnormality that generally requires no specific treatment as it's usually benign and asymptomatic, but patients should undergo evaluation for underlying heart disease. The diagnosis of LAFB is based on specific ECG 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 American Heart Association recommendations 1. Key points to consider in the management of LAFB include:
- Evaluation for underlying heart disease, such as coronary artery disease, hypertensive heart disease, cardiomyopathy, or degenerative conduction system disease
- Monitoring for progression to more complex conduction disorders, such as bifascicular block or trifascicular block, which may increase the risk of complete heart block
- Regular cardiac follow-up with ECGs, especially if the patient develops symptoms like syncope, presyncope, or worsening heart failure The pathophysiology of LAFB involves fibrosis or sclerosis of the conduction tissue in the left anterior fascicle, leading to delayed electrical impulse transmission to the anterolateral left ventricle. It is essential to note that the management of LAFB focuses on the underlying cause and associated conditions rather than the block itself, and the recent guidelines for atrial fibrillation management 1 do not directly apply to the treatment of LAFB.
From the Research
Definition and Diagnosis of Left Anterior Fascicular Block
- Left anterior fascicular block (LAFB) is a heart condition characterized by abnormal electrocardiogram (ECG) patterns 2, 3, 4.
- The diagnosis of LAFB is based on ECG criteria, including marked left axis deviation (LAD) and delayed intraventricular conduction 2.
- However, the relationship between LAD and delayed intraventricular conduction is not always consistent, and LAD alone should not be considered synonymous with LAFB 2.
ECG Patterns and Clinical Significance
- LAFB can decrease the voltage in chest leads and increase the voltage in limb leads, and can also cause changes in repolarization, including decreased T waves in leads I and aVL 3.
- LAFB can mask or mimic infarction and left ventricular hypertrophy, and can also mask right bundle branch block in the setting of an acute anterior myocardial infarction 3.
- A study using a whole-heart model-based simulation found that impaired conduction in the ventricular myocardium can lead to abnormal ECG patterns similar to LAFB 4.
Prognostic Significance and Relation to Coronary Artery Disease
- LAFB is associated with an increased risk of heart failure and cardiac death 5.
- A retrospective study found that LAFB subjects had more pathological coronary artery disease (CAD) and myocardial infarction (MI), but LAFB was not an independent relevant factor of CAD 5.
- LAFB can lower the accuracy of clinically diagnosing CAD, and LAFB patients have heavier hearts, thicker left ventricular walls, and an increased risk of death and cardiac death 5.