Left posterior fascicular block

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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.^[1] Its seen either in the setting of either RCA or LAD related pathologies.

The electrocardiogram findings in left posterior fascicular block include right axis deviation of the QRS complex, wide QRS complexes and a S1Q3 pattern.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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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. ^[1]

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.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ayokunle Olubaniyi, M.B,B.S [2]

Isolated left posterior fascicular block is often an uncommon finding^[1] owing to the fact that the left posterior fascicle has a dual blood supply, and it is exposed to lower pressures and turbulence, hence, it is rarely damaged. It usually accompanies right bundle branch block (RBBB) or in the setting of arteriosclerotic heart diseases such as myocardial infarction. Other less common causes include: infectious (e.g. diphteritic myocarditis, Chagas disease); genetic (e.g. myotonic dystrophy).

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Hyperkalemia
• Myocardial infarction

• Cardiomyopathy
• Coronary artery disease
• Hypertensive heart disease
• Myocardial infarction

• Cor pulmonale
• Cardiomyopathy
• Chagas disease
• Coronary artery disease
• Diphteritic myocarditis
• Hyperkalemia
• Hypertensive heart disease
• Kearns-Sayre syndrome
• Limb-girdle muscular dystrophy
• Myocardial infarction
• Myotonic dystrophy

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