I44.4

Left anterior fascicular block (I44.4): left axis deviation, causes, bifascicular block and management.

Left anterior fascicular block (LAFB, ICD-10 I44.4) is a conduction delay in the anterior branch (fascicle) of the left bundle branch. The anterior and upper parts of the left ventricle are then activated late, through the posterior fascicle, so the electrical axis of the heart shifts upwards and to the left. LAFB is the most common intraventricular conduction disturbance; it is related to, but distinguished from, left bundle branch block, because only part of the left bundle is affected and the QRS remains narrow.

ICD-10 I44.4Fascicular blockLeft axis deviation

Frontal QRS axis−45° to −90°

LeadsqR in aVL, rS in II, III, aVF

QRS duration< 120 ms

With RBBBbifascicular block

Figure 1. Typical LAFB: qR in lead aVL (left) and rS in lead III (right), corresponding to a QRS axis of about −60°.

Causes

Hypertension and left ventricular hypertrophy
Coronary artery disease and previous anterior myocardial infarction
Aortic valve disease and transcatheter aortic valve implantation
Cardiomyopathies, myocarditis, Chagas disease, infiltrative diseases
Age-related fibrosis of the conduction system (Lev and Lenègre disease); it may also be found in otherwise healthy people

Significance and management

Isolated LAFB itself causes no symptoms and needs no specific treatment, but it can be a marker of underlying heart disease, so an assessment of blood pressure, cardiovascular risk factors and, when indicated, echocardiography is reasonable. When LAFB is combined with right bundle branch block (bifascicular block), only the posterior fascicle conducts; if fainting occurs, monitoring and electrophysiological testing are used to look for intermittent complete heart block, which is treated with a pacemaker. LAFB can also mimic or mask other ECG findings (for example inferior infarction or left ventricular hypertrophy).

When to see a doctor

Fainting, dizziness, breathlessness or chest pain in a person with LAFB, especially combined with bundle branch block, need prompt cardiological assessment.

References

Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances. Circulation. 2009;119(10):e235–e240. doi:10.1161/CIRCULATIONAHA.108.191095
Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628

This article is for general information and does not replace a consultation with a doctor. Diagnosis and treatment must be decided by a physician on the basis of symptoms, examination and tests.

Published on 24 March 2019