From the Guidelines
Left anterior fascicular block (LAFB) is diagnosed 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 2009 American Heart Association recommendations 1. When evaluating a patient with suspected LAFB, it is essential to consider these criteria to ensure accurate diagnosis. The ECG findings for LAFB include:
- Frontal plane axis between 45° and 90°
- qR pattern in lead aVL
- R-peak time in lead aVL of 45 ms or more
- QRS duration less than 120 ms According to the American Heart Association recommendations 1, these criteria are crucial for the standardization and interpretation of the electrocardiogram. In clinical practice, LAFB is often asymptomatic and may not require specific treatment when isolated. However, it is crucial to evaluate for underlying heart disease, such as coronary artery disease, cardiomyopathy, or valvular heart disease, as LAFB can be associated with these conditions. Regular cardiac follow-up is recommended, especially if there are other conduction abnormalities present, as LAFB can be part of a progressive conduction disease. The presence of LAFB should prompt consideration of cardiac risk factors and appropriate management of any underlying cardiovascular conditions to prevent progression of heart disease, as emphasized in the 2009 American Heart Association recommendations 1.
From the Research
Left Anterior Fascicular Block
- Left anterior fascicular block (LAFB) is a condition that affects the electrical conduction system of the heart, specifically the left anterior fascicle 2.
- The electrocardiographic criteria for LAFB include left axis deviation and delayed intraventricular conduction, although the validity of these criteria has been questioned 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 2.
Diagnosis and Prognosis
- The diagnosis of LAFB is typically made using electrocardiography (ECG), although the criteria for diagnosis are not always clear-cut 3.
- LAFB has been associated with an increased risk of adverse cardiovascular outcomes, including syncope, pacemaker implantation, and complete heart block 4.
- The presence of LAFB can also lower the accuracy of clinical diagnosis of coronary artery disease (CAD) 5.
- LAFB has been shown to be an independent risk factor for all-cause death and cardiac death, with cardiac death being the major cause of death in patients with LAFB 5.
Clinical Significance
- LAFB is more common in older patients and is often associated with CAD and myocardial infarction (MI) 5.
- Patients with LAFB are more likely to have heavier hearts and thicker left ventricular walls than those without LAFB 5.
- The presence of LAFB can have significant clinical implications, including an increased risk of cardiac complications and death 4, 5.
- Care should be taken to preserve normal blood flow to the septal perforators during elective intervention to the left anterior descending artery (LAD) territory in patients with prior conduction abnormalities on the ECG, including LAFB 6.