Bundle branch block (BBB) is an abnormality of the heart’s electrical conduction system in which one of the two main branches carrying electrical impulses to the ventricles (the left or right bundle branch) is partially or completely blocked. This forces the affected ventricle to depolarise more slowly via an alternative route, producing a characteristic widened QRS complex on the ECG.
There are two main types. Left bundle branch block (LBBB) affects the left ventricle and is more often associated with significant underlying heart disease such as coronary artery disease, cardiomyopathy, or heart failure. Right bundle branch block (RBBB) can be seen in structurally normal hearts but may also be associated with conditions including pulmonary embolism, congenital heart disease, and Brugada Syndrome.
New-onset LBBB in the context of chest pain is treated as a possible heart attack until proven otherwise. In heart failure with a wide LBBB, Cardiac Resynchronisation Therapy (CRT) can improve symptoms and outcomes by electrically coordinating both ventricles. Bundle branch block alone does not directly cause cardiac arrest but may indicate underlying structural disease that does.
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