29 January 2018



The heart has a unique electrical system to synchronize its contractions in an effective way. The orchestra conductor of this electric system is located all at the top of the heart, at the level of the right atrium.

The transmission of the electrical signal from the atria to the ventricles is only possible at a gateway called atrioventricular node.

Once passed this gateway, electricity is transmitted to the right and left ventricles through two specialized electrical branches, the Purkinje network. These bundles, right and left, promptly transmit electricity to the bottom of the ventricles to allow a synchronized contraction from the bottom to the top of the heart.




Defects of electrical conduction by the two specialized branches of the ventricles can occur.

One calls these conditions bundle branch blocks - right if it affects the right branch and left if it affects the left branch.

This block can be intermittent (not always present). In certain cases, the block depends on the heart rate. It appears at a certain heart rate and disappears when the heart rate goes down again.

One calls this condition ‘’rate-dependent branch block”.

The branch blocks can be permanent. They are thus constantly present.

They are highlighted on the electrocardiogram


​What happens when a branch is block

When a branch is blocked, the electrical transmission is by continuity, that is to say as the transmission of a wave in the water, from the branch that works to the one that does not work anymore


Right bundle branch block

In the case of a right bundle branch block, the transmission of electricity in the ventricles will be done initially in the left ventricle, then towards the right ventricle. 






ECG normal




ECG With right block. The peaks are wider by slow condudtion in the right ventricule






Left bundle branch block

The same principle applies for a left bundle branch block.








ECG normal



ECG With left Block.The peaks are wider by slow conduction in the left ventricule.




What causes a bundle branch block?

In the majority of the cases, there is no identifiable disease.  However, it is sometimes related to diseases of the heart muscle (heart attack, muscle thickening, dilatation of the ventricles) or some birth defects (called congenital).

A bundle branch can be related to any disease that affects the septum, the muscular division between the two ventricles where those bundle branches are located.  


No symptom

Right or left bundle branch blocks do not cause any symptom.


No need for a pacemaker

There is no need for a pacemaker (cardiac stimulator) in those situations. But it doesn't mean that a pacemaker will be required one day.

​Possible additional tests

​To make sure that bundle branch block is not related to an underlying heart disease, the physician may order additional tests.He may order an echocardiogram to assess the heart structure and to detect any anomaly.

A test to assess oxygen delivery to the heart may also be ordered. It could be a stress test on the treadmill, a nuclear scan or a stress echocardiogram. During those tests, your heart will be put under stress by the effective exercise or by injecting a medication to stimulate your heart.



Related articles


A problem with the rhythm, or arrhythmia, is a problem with the electric system that makes the heart beat. There are two main categories of problems: stimulation disorders and conduction disorders.

View more


The heart has its own electrical system. Its function is to synchronize the muscle contraction in an effective way.

View more


Electrocardiogram (ECG) is a 10 seconds recording of the electricity of the heart

View more


The treadmill is a test in cardiology that evaluates, indirectly, possible blockages in the coronary arteries. It also helps evaluate the cardiovascular condition.

View more


A Holter monitoring is a continuous recording of the ECG, the electricity generated by your heart, during 24 hours.

View more


It is the same type of test used to examine a baby in a pregnant woman. In the case of a cardiac ultrasound, the heart is organ of interest.

View more