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Left Bundle Branch Block

Image 2 of 2 in Series "Bundle Branch Blocks"

Description

A bundle branch block is characterized by an extended QRS complex of 0.12 seconds or more. This ECG finding is caused by the blockage of conduction in the left bundle branch, delaying depolarization to the left ventricle. Initial depolarization of the basal septum proceeds from left to right, resulting in a small R wave in lead V1. Depolarization then proceeds from the right to the left, resulting in R waves in the lateral leads and deep S waves in the right precordial leads.

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This image is part of the series "Bundle Branch Blocks"

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Right Bundle Branch Block

by: Caleb Bacak, BA, BS; Joe B. Calkins, Jr., M.D.

A bundle branch block is characterized by an extended QRS complex of 0.12 seconds or more. This ECG finding is caused by the blockage of conduction in the right bundle branch, delaying depolarization of the right ventricle. The small R wave (r wave) in lead V1 is caused by depolarization of the interventricular septum proximal to the block in the right bundle, which proceeds in a left to right direction. Because the right bundle is blocked, depolarization then proceeds from the right to the left, resulting in R waves in the lateral leads and S waves in the right precordial leads. Depolarization then proceeds from the left to right across the muscular interventricular septum, resulting in an R’ wave in the right precordial leads, an S wave in the lateral leads and a widened QRS complex.