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The Merck Manual--Second Home Edition logo
 
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Chapter 27. Abnormal Heart Rhythms
Topics: Introduction | Atrial Premature Beats | Atrial Fibrillation and Atrial Flutter | Paroxysmal Supraventricular Tachycardia | Wolff-Parkinson-White Syndrome | Ventricular Premature Beats | Ventricular Tachycardia | Ventricular Fibrillation | Pacemaker Dysfunction | Heart Block | Bundle Branch Block
 
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Bundle Branch Block

Bundle branch block is a type of conduction block involving partial or complete interruption of the flow of electrical impulses through the right or left bundle branches.

The bundle of His is a group of fibers that conducts electrical impulses from the atrioventricular node. The bundle of His divides into two bundle branches (see Section 3, Chapter 20). The left bundle branch conducts impulses to the left ventricle, and the right bundle branch conducts impulses to the right ventricle. Conduction may be blocked in the left or right bundle branch.

Bundle branch block usually causes no symptoms. Right bundle branch block is not serious in itself and may occur in apparently healthy people. However, it may also indicate significant heart damage due to, for example, a previous heart attack. Left bundle branch block tends to be more serious. In older people, it often indicates heart disease due to high blood pressure or atherosclerosis.

Bundle branch block can be detected by electrocardiography (ECG) (see Section 3, Chapter 21). Each type of block produces a characteristic pattern. Usually, no treatment is needed for either type. However, an artificial pacemaker (see Section 3, Chapter 27) may be implanted in people who are at high risk of complete heart block (such as people with second-degree heart block) to maintain the heart rate if complete heart block occurs.

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