Harvard Heart Letter

Ask the doctor: Is bundle branch block serious?

Ask the doctor

Is bundle branch block serious?

Q. I had an electrocardiogram in preparation for minor surgery. My doctor told me it showed that I have right bundle branch block. Neither he nor my cardiologist are worried about it, but I am. Is this serious?

A. Much of the time, bundle branch block is not serious. If your doctors are telling you it's okay, I would trust them.

The term bundle in this condition refers to a collection of nerve fibers that take the "contract now" signal from the heart's natural pacemaker and spread it through the ventricles, the heart's lower chambers. The right bundle branch delivers the signal to the right ventricle, the left bundle branch to the left ventricle (see "Pathways for contraction"). The electrical signal is supposed to move at the same speed through both bundles so the right and left ventricles contract at the same time. If the signal is blocked in one of these pathways, the ventricle with the block will contract a fraction of a second later than the other ventricle. If the heart is otherwise healthy, this slightly out-of-sync beat doesn't usually cause any symptoms.

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