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Causes
By Mayo Clinic staff
Normally, electrical impulses within your heart's muscle signal it to beat (contract). These impulses travel along a pathway, passing from your heart's upper chambers (atria) through a small mass of cells called the atrioventricular (AV) node and then to the lower chambers (ventricles).
Along the route on this pathway, the impulses move along a slender cluster of cardiac fibers called the "bundle of His," which divides into two branches — the right and the left bundles — one for each of the heart's ventricles.
If one or both of these branch bundles become damaged — due to a heart attack, for example — this change can prevent your heart from beating normally. The heart's electrical impulses that make your heart beat may be slowed down or blocked. When this occurs, the ventricles no longer contract in perfect coordination with one another.
Bundle branch block may be caused by:
- A heart attack (myocardial infarction)
- Thickened, stiffened or weakened heart muscle (cardiomyopathy)
- A viral or bacterial infection of the heart muscle (myocarditis)
- High blood pressure (hypertension)
- Scar tissue that develops after heart surgery
- A heart abnormality that's present at birth (congenital) — such as atrial septal defect, a hole in the wall separating the upper chambers of the heart
