Bundle Branch Block

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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.


A bundle branch block is an anomaly in the electrical conduction system of the heart.

A blockage can occur in either of the two specialized branches of the electrical transmission system when impulses travel to the right and left ventricles.

These conditions are called bundle branch blocks: the right bundle branch block affects the right branch and the left one affects the left branch.
Bundle branch blocks can be either intermittent or permanent.

-Intermittent Bundle Branch Block

  • Rhythm-dependent branch block.

A branch may stop conducting electrical impulses when the heart rate accelerates. This is called a “rhythm-dependent bundle branch block”. Branch blocks can develop above a certain rate and disappear when the heart rate drops.

An example:

For instance, consider the case of a person who comes in for a treadmill stress test. Walking at a quicker pace leads to faster heartbeats, consequently increasing blood flow to all the muscles involved.

A bundle branch block may occur when the heart rate exceeds, say, 120 beats per minute. The person does not feel any symptoms whatsoever at this time.

However, the electrocardiogram shows changes associated with a bundle branch block. Ventricular conduction returns to normal with the disappearance of the blockage during the rest period while the heart rate falls below 120 beats per minute.

-Permanent Bundle Branch Block

A bundle branch block can be permanent, which means that it is continuously present.


Whether intermittent or permanent, bundle branch blocks are always recorded on electrocardiograms.

Electrical conduction with bundle branch block

When a branch is blocked, the electrical system takes place by continuity from one heart cell to another, much like the sinuous movement of a wave, from the functioning branch to the non-functioning one.

As the conduction is slower than when done with two intact networks, the signal shown on the ECG is enlarged and distinctive of the branch that is blocked.


Right Bundle Branch Block

In the case of a right bundle branch block, the transmission of electricity to the ventricle will occur first in the left ventricle, then to the right one. 

Normal ECG versus ECG with Right Bundle Branch Block

Left Bundle Branch Block

As for the left bundle branch block, a similar sequential order is followed, but this time from the right ventricle to the left one.

Normal ECG versus ECG with Left Bundle Branch Block

The number one cause is that there is none

In the majority of bundle branch blocks, and especially in the case of the Right Branch Block, there is no connected identifiable disease.

A Left Bundle Branch Block may be secondary to an underlying disease. However, it is more frequently a sign of cardiac disease that should be investigated.

Possible causes

The possible causes of bundle branch blocks are related to the cardiac muscle, namely infarctions, hypertrophy, progressive cardiac conduction defect, aortic valve disease and some specific birth defects.

We can also find the sources of dilatation, and muscular hypertrophy of the ventricles, not to mention the problems of oxygenation, among others angina, or those that are secondary to myocardial infarctions.

In short, the right or left bundle branch block can be related to any disease that affects the septum, which is the partition between the two ventricles and serves as a conduit for these specialized electrical wires.

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.

Follow up

Le professionnel de la santé poursuivra son intervention en fonction des résultats obtenus lors de son investigation.

Important Information to Remember

It is crucial for the patient to be informed about the presence of a bundle branch block, as this is crucial during preoperative investigation.

Mentioning the knowledge of this block and the investigations conducted at the time of its discovery helps avoid repeating already performed exams and prevents delaying the procedure.