From the Guidelines
Left anterior fascicular block (LAFB) is generally a benign conduction abnormality that rarely requires specific treatment on its own, but it may indicate underlying heart disease and necessitates a thorough cardiac evaluation to identify and manage any underlying conditions.
Implications of LAFB
The implications of LAFB are primarily related to its potential to indicate underlying heart disease, such as coronary artery disease, cardiomyopathy, or hypertensive heart disease, rather than the block itself causing significant symptoms or morbidity 1.
Diagnosis and Management
LAFB is characterized by a specific ECG pattern showing left axis deviation, small Q waves in leads I and aVL, and small R waves in leads II, III, and aVF. Management of LAFB focuses on identifying and treating any underlying cardiac condition, with no specific medication needed to treat isolated LAFB 1.
Risk of Progression
If LAFB progresses to bifascicular block (with right bundle branch block) or develops new conduction abnormalities, closer monitoring is warranted as this increases the risk of complete heart block 1.
Follow-up and Monitoring
Patients with LAFB should undergo a cardiac evaluation, including echocardiography to assess for structural heart disease, and follow up regularly with a cardiologist, especially if they have other cardiac risk factors or symptoms like syncope, presyncope, or palpitations 1.
Pathophysiology
LAFB occurs due to fibrosis or ischemia affecting the anterior fascicle of the left bundle branch, disrupting the normal electrical activation sequence of the ventricles 1.
Prognosis
The prognosis for patients with LAFB is generally favorable, especially when compared to other conduction abnormalities, such as left bundle-branch block or bifascicular block 1.
Key Considerations
In clinical practice, the presence of LAFB should prompt a thorough evaluation for underlying heart disease and regular monitoring for potential progression to more severe conduction abnormalities 1.
From the Research
Implications of Left Anterior Fascicular (LAF) Block
- A LAF block can lead to a variable duration of the QRS complex, which is dependent on the length of the cycle, being broader with short than with long preceding R-R intervals 2.
- The block can be 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 can also contribute to heart failure 3.
- LAF block can mask or mimic infarction and left ventricular hypertrophy, and mask right bundle branch block in the setting of an acute anterior myocardial infarction 4.
- The incidence of postprocedural LAF block after transcatheter closure of a ventricular septal defect is not low, but the overall prognosis is quite good, with most patients gradually returning to normal within 1-2 years 5.
- A high ratio between VSD size and body surface area and a large diameter difference between the occluder size and VSD size are independent risk factors for postprocedural LAF block 5.
- LAF block can also be a complication of percutaneous coronary intervention to the left anterior descending artery, and care should be taken to preserve normal blood flow to the septal perforators to avoid complete atrioventricular block 6.