From the Research
Anterior fascicular block, also known as left anterior fascicular block (LAFB), is a cardiac conduction abnormality that generally does not require specific treatment, but may indicate underlying heart disease and necessitate closer monitoring, especially when combined with right bundle branch block (bifascicular block) 1.
Diagnosis and Presentation
Anterior fascicular block is diagnosed on an electrocardiogram (ECG) by a leftward axis deviation (typically -45 to -90 degrees), small Q waves in leads I and aVL, and small R waves in leads II, III, and aVF. Most patients with anterior fascicular block are asymptomatic, but it may be associated with an increased risk of heart failure and conduction disturbances 2.
Management and Prognosis
When found incidentally, a basic cardiac evaluation including a complete history, physical examination, and possibly an echocardiogram may be warranted to rule out structural heart disease. The presence of anterior fascicular block in combination with right bundle branch block (bifascicular block) requires closer monitoring as it may progress to complete heart block, with a 10-year risk of developing third-degree AVB ranging from 0%-2% for isolated LAFB to up to 23% for bifascicular block with first-degree AVB 1. Patients with syncope or presyncope and bifascicular block may need electrophysiology studies to assess the need for a pacemaker 3.
Associated Conditions and Complications
Anterior fascicular block may be associated with underlying heart disease such as coronary artery disease, cardiomyopathy, or degenerative conduction system disease. Patients with atrial septal defects have a higher prevalence of conduction abnormalities, including anterior fascicular block, and may require closer monitoring and potential pacemaker implantation 4. Additionally, percutaneous coronary intervention to the left anterior descending artery can lead to complete atrioventricular block and necessitate permanent pacemaker implantation 5.