Left posterior fascicular block

Left posterior fascicular block
ICD-10	I44-I45
ICD-9	426.9
DiseasesDB	10477
MeSH	D006327

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Synonyms and keywords: LPFB; Left Posterior Hemiblock; LPH

Overview

Left posterior fascicular block is characterized by a mean frontal plane axis of >90° in the absence of other causes of right axis deviation. Left posterior hemiblock (left posterior fascicular block) is infrequent. Its seen either in the setting of either RCA or LAD related pathologies.

Anatomical Course of the Left Fascicle

The left posterior fascicle is a distal extension of the left main bundle and courses posteriorly toward the posterior papillary muscle which is located in the posterior, medial and inferior aspect of left ventricle and inferoposteriorly toward the left ventricular free wall.

Blood Supply of the Left Posterior Fascicle

The proximal part of the left posterior fascicle is supplied by the artery supplying the atrioventricular (AV) node (often the right coronary artery) and, at times, by septal branches of the left anterior descending (LAD) artery.

Causes

• Congenital aortic stenosis
• Congenital heart disease repair
• Endocarditis
• Myocarditis secondary to diphtheria

Diagnosis

The diagnosis is often made in the context of previous ECGs. The frontal QRS axis is rightward and there are no other potential causes of right axis deviation such as right ventricular hypertrophy and prior lateral myocardial infarction.

• QRS axis of 100 to 180 degrees
• QRS duration 80-100 msec (usually normal or slightly widened qRS complex)
• Deep S in lead I and aVL (rS in I and aVL)
• qR in II, III, and aVF