From the Guidelines
Left Anterior Fascicular Block (LAFB) Definition
Left anterior fascicular block (LAFB) is a type of heart block that affects the electrical conduction system of the heart, characterized by a blockage in the left anterior fascicle, resulting in a change in the direction of the electrical impulse [ 1 ].
Key Characteristics
The key characteristics of LAFB include:
- A frontal plane axis between 45° and 90° [ 1 ]
- A qR pattern in lead aVL [ 1 ]
- An R-peak time in lead aVL of 45 ms or more [ 1 ]
- A QRS duration less than 120 ms [ 1 ]
- A shift in the QRS vector in a posterior and superior direction, resulting in larger R waves in leads I and aVL and smaller R waves but deeper S waves in leads V5 and V6 [ 1 ]
Clinical Implications
LAFB is often associated with underlying heart conditions such as coronary artery disease, hypertension, and cardiomyopathy. The presence of LAFB can make it challenging to diagnose left ventricular hypertrophy (LVH) using traditional ECG criteria, as the R-wave amplitude in leads I and aVL are not reliable criteria for LVH in this situation [ 1 ]. However, criteria that include the depth of the S wave in left precordial leads can improve detection of LVH in the presence of LAFB [ 1 ].
Diagnosis and Treatment
Diagnosis of LAFB is typically made using an electrocardiogram (ECG), and treatment usually focuses on managing the underlying condition [ 1 ]. Medications such as beta blockers, ACE inhibitors, and anti-arrhythmic medications may be prescribed, and in some cases, a pacemaker may be implanted to help regulate the heartbeat. It is essential to consult a cardiologist for proper diagnosis and treatment.
From the Research
Definition of Left Anterior Fascicular (LAF) Block
- Left Anterior Fascicular Block (LAFB) is a heart condition characterized by an abnormal electrocardiogram (ECG) pattern, which can be associated with an increased risk of heart failure 2, 3.
- LAFB is diagnosed based on ECG criteria, including 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.
ECG Patterns and Diagnosis
- ECG patterns of LAFB can reveal diverse patterns on scintigraphic phase analysis, and phase analysis can be useful in assessing the diagnosis of LAFB 4.
- Simulation studies have shown that typical LAFB ECG patterns can also be observed from cases with slowed conduction velocity in the ventricular myocardium, with differences in the duration of QRS and wave amplitude 3.
- Transient LAFB can occur as a consequence of proximal subocclusion of the left anterior descending coronary artery, and can be associated with left septal fascicular block (LSFB) 5.
Clinical Significance and Prognosis
- LAFB is associated with coronary artery disease (CAD), myocardial infarction (MI), and myocarditis, and can lower the accuracy of clinically diagnosing CAD 6.
- LAFB patients have heavier hearts, thicker left ventricular walls, and are at increased risk of death and cardiac death, with cardiac death being the major cause of death in LAFB patients 6.
- Logistic regression has shown that CAD is not an independent relevant factor of LAFB, but LAFB is an independent risk factor of all-cause death and cardiac death 6.