Bundle branch blocks
Left bundle branch block
What is left bundle branch block?
Bundle branch block is a disorder that affects the heart’s electrical conduction system and causes a blockage of the regular electrical signals that tell it when and how to contract.
Heart contractions: LBBB vs normal heart
Normally, your heart sends electrical signals from the sinoatrial (SA) node, the heart’s natural pacemaker, down to the atrioventricular (AV) node and then on to the bundle of His, which is a collection of muscle fibers specialized for transmitting electrical impulses.
The bundle of His then divides the signal into left and right branches and sends it on to the ventricles, the heart’s lower chambers, where it tells them when to contract.
If you have bundle branch block, the signals from the bundle of His to either your left or right ventricle are delayed or blocked.
In left bundle branch block (LBBB) the left-hand electrical pathway is interrupted. The signal still reaches your left ventricle, but it travels there through your right ventricle and gets there slightly late.
This can cause the contraction of your ventricles to be uncoordinated and it can make your heart’s pumping mechanism less efficient.
In some people with LBBB the blockage may be present all the time, but in others it may be intermittent, only happening when exercising or at other times when their heart rate is quite high.
If you want learn more about a normal heartbeat take a look at Your heart: The basics.
What causes left bundle branch block?
Some people with LBBB were born with it, but for most people it develops as a result of some kind of damage to the heart’s conduction system.
To learn more about how your heart’s conduction pathways and how they work, take a look at Your heart’s electrical system.
Electrical signals: LBBB vs normal heart
Coronary artery disease, a heart attack, and various types of cardiomyopathy (heart muscle weakness or thickening) can all cause LBBB, as can any disorder that causes heart inflammation (myocarditis, for example).
Some people with LBBB have structurally normal hearts with no sign of any damage. It’s not clear what causes the LBBB in cases like this but it is probably age-related.
Common causes of LBBB include:
- Cardiomyopathy (heart muscle weakness or enlargement)
- Heart attack
- Congenital conditions: Many people who have LBBB were born with it
What are the symptoms of left bundle branch block?
Usually, people with LBBB don’t experience any symptoms. You may not even be aware that you have it.
However, if you have other underlying heart problems, such as heart failure or coronary artery disease, LBBB may make the symptoms of those disorders worse.
If you do experience symptoms, they may include:
- Light-headedness or fainting
- Difficulty breathing during exercise
- Slow heart rate
How is left bundle branch block treated?
If you have no symptoms, you may not need any treatment at all for LBBB. However, if your LBBB is related to other heart or circulation disorders like heart failure or coronary artery disease, your doctor will want to treat those disorders.
If your LBBB, in combination with an underlying disorder, is causing troubling symptoms, you may need to have a biventricular pacemaker inserted. A biventricular pacemaker will synchronize the beating of the right and left ventricles.
Treatments for LBBB, when needed, include:
- Surgical insertion of a biventricular pacemaker
- Treatment of any other heart or circulation disorders that may be causing additional problems
What are the aims of treatment?
The aim of treatment for people with LBBB that is causing troubling symptoms is to improve the efficiency of the heart’s pumping mechanism by treating any other underlying disorders and, in cases where a biventricular pacemaker is inserted, to help the heart beat at a normal rate.