Bundle branch block
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Synonyms and keywords: BBB
For detailed medical information on Left Bundle Branch Block click here.
For detailed medical information on Right Bundle Branch Block click here.
Overview
A bundle branch block refers to a defect of the heart's electrical conduction system below the level of the AV node. Depending upon the level and location of the block/defect in the conducting pathway bundle branch block can be classified into left bundle branch block and right bundle branch block.
Pathphysiology
- Main article: Electrical conduction system of the heart
Diagnosis
Electrocardiogram
A bundle branch block can be diagnosed when the duration of the QRS complex on the ECG exceeds 120 ms. A right bundle branch block typically causes prolongation of the last part of the QRS complex, and may shift the heart's electrical axis slightly to the right. The ECG will show a terminal R wave in lead V1 and a slurred S wave in lead I. Left bundle branch block widens the entire QRS, and in most cases shifts the heart's electrical axis to the left. The ECG will show a QS or rS complex in lead V1 and a monophasic R wave in lead I. Another normal finding with bundle branch block is appropriate T wave discordance. In other words, the T wave will be deflected opposite the terminal deflection of the QRS complex.
Treatment
Many people with bundle branch blocks may still be quite active, and may have nothing more remarkable than an abnormal appearance to their ECG. However, when bundle blocks are complex and diffuse in the bundle systems, or associated with additional and significant ventricular muscle damage, they may be a sign of serious underlying heart disease. In more severe cases, a pacemaker may be required to re-establish better heart muscle function.
Related Chapters
- Electrical conduction system of the heart
- Cardiac pacemaker
- Heart blocks
- First degree AV block
- Second degree AV block
- Third degree AV block
- Right bundle branch block
- Left bundle branch block
- Bifascicular block
- Trifascicular block