Think of it as the “motherboard”…every little artery and channel has a function.
When the heart is healthy, each of those functions serves to keep you alive by interacting with everything else in your body. But as with any electrical system, one glitch could bring the whole thing down.
So, if we want to live the best lives we can, it’s important to understand why and how things go wrong, and the effects it has on our lives.
One of the challenges when learning about heart rhythms comes with being given a diagnosis of Bundle Branch Block.
The discovery process begins when your electrocardiogram (ECG/EKG)) displays a distinctive, abnormal pattern.
A perfectly functioning heart stays in what is called “Normal Sinus Rhythm.” This is the characteristic rhythm of a healthy human heart, and it originates from the sinus node. It looks like this:
The abnormal pattern of a bundle branch block, by contrast, looks like this:
The cardiac electrical system has two bundle branches – the right and the left.
➡ In Bundle Branch Block, one or the other of these bundle branches is blocked and no longer conducting electrical impulses normally.
The course of treatment varies from person to person, depending on other health issues, so it is important for you to discuss this ECG finding thoroughly with your doctor.
This article will guide you through some of the terminologies, and hopefully, improve your communications with the medical professionals responsible for your care.
When you speak to your physician about it, you’ll be ready to discuss the issues as they apply to you specifically and know which questions to ask. So here we go…
The bundle branches are an important part of the cardiac electrical system, the system that regulates the heart rhythm and coordinates the pumping action of the heart.
The branches work to evenly distribute the spread of the cardiac electrical impulse across the ventricles, so that when the ventricles contract (to eject blood out of the heart), they do so in a coordinated and efficient fashion.
The Normal Cardiac Electrical System
- ➡ The heart’s electrical impulse starts in the sinus node (top left of the photo), located in the upper right atrium, then spreads across both atria
➡ It then travels through the AV (atrioventricular) node.
➡ Leaving the AV node, the electrical impulse penetrates into the ventricles via “the HIS bundle.”
➡ From the HIS bundle, the electrical impulse enters the two bundle branches (the right and the left).
➡ The right and left bundle branches then send the electrical impulse to the right and left ventricles, respectively.
- When the bundle branches are functioning normally, the right and left ventricles contract nearly simultaneously.
Bundle Branch Block occurs when one of the bundle branches becomes diseased or damaged, and stops conducting electrical impulses; that is, one of the bundle branches becomes “blocked.”
The effect of a bundle branch block is a disruption in the normal, coordinated and simultaneous contraction of the two ventricles.
In other words, the contraction of one ventricle (the one whose bundle branch is blocked) happens slightly after the contraction of the other. That is now an abnormal heart rhythm.
Right Bundle Branch Block
RBBB is a relatively common ECG finding, and while it occurs in a variety of medical conditions, it’s also found in some people whose hearts are completely normal.
➡ It often occurs in medical conditions that affect the right ventricle or the lungs, so a finding of RBBB on the ECG should trigger a screening exam for such conditions.
They include: (click each link to learn more about each)
➡ Blood clots in the lung
➡ Coronary Artery Disease (CAD)
If you are told you have Right Bundle Branch Block, however, keep in mind that this ECG pattern also occasionally occurs in normal, healthy people, and your medical evaluation may turn up no medical problems at all.
- In this case, the RBBB has no clear medical significance, and can be written off as a “normal variant” and safely ignored.
While the presence of RBBB means that the right ventricle begins to contract slightly after the left ventricle, in normal hearts this delay in right ventricular contraction causes no measurable decrease in cardiac function.
➡ In Right Bundle Branch Block, the right bundle branch no longer conducts electricity. So the heart’s electrical impulse enters the ventricles using only the left bundle branch – which means the left ventricle receives the electrical impulse first.
➡ Then, from the left ventricle, the electrical impulse finally makes its way to the right ventricle.
➡ As a result, the two ventricles no longer receive the electrical impulse simultaneously. First, the left ventricle receives the electrical impulse, then the right.
Left Bundle Branch Block
In Left Bundle Branch Block, the opposite happens.
➡ Here, the left bundle branch no longer conducts electricity. So the electrical impulse enters the ventricles through the right bundle branch and is carried first to the right ventricle.
➡ From there, it finally spreads to the left ventricle.
Once again, the two ventricles no longer receive the electrical impulse simultaneously. First, the right ventricle receives the electrical impulse, then the left.
Therefore, with either type of Bundle Branch Block, the electrical signal spreads across the ventricles one after the other instead of at the same time.
- This sequence of spreading the impulse (i.e., first the right ventricle, then the left, or vice versa) means that it takes longer for the impulse to spread throughout both ventricles.
LBBB is somewhat less common than RBBB, and its presence usually indicates underlying cardiac complications.
Left Bundle Branch Block is commonly seen with the following cardiac conditions (click each link to learn more about each).
➡ Hypertension (high blood pressure)
➡ Coronary Artery Disease, and a variety of other cardiac conditions.
While occasionally Left BBB occurs in “apparently healthy” people, its appearance should trigger a thorough search (as opposed to a simple screening) for underlying cardiac problems.
In some people – especially in patients with heart failure and reduced left ventricular ejection fractions – the fact that the contraction of the left ventricle is delayed in LBBB actually does cause a measurable decrease in cardiac efficiency and cardiac function.
What If Both Bundle Branches Are Blocked?
If both the right and left bundle branches are completely blocked, the electrical impulse will not be able to reach the ventricles at all.
This is a form of “complete heart block.” The ventricles stop beating and death occurs.
Fortunately, this form of complete heart block (also called 3rd Degree Heart Block) is uncommon.
More commonly, both bundle branches can be damaged to the extent that they conduct the electrical impulses more slowly than normal, but neither is completely blocked.
The most important fact in understanding a diagnosis of Bundle Branch Block is that it may indicate the presence of previously unknown underlying cardiovascular disease.
When Does Bundle Branch Block Need to Be Treated?
- Normal cardiac function depends on the two bundle branches. If they both were to completely stop working (producing complete heart block), the electrical impulse could not be delivered to the ventricles, and the heart would stop beating.
There are three circumstances in which people with BBB might need a pacemaker:
1) When disease in both the right and left bundle branches appears after an acute heart attack.
➡ When a patient develops new evidence of disease in both the right and left bundle branches right after a heart attack, there is a greatly increased chance of developing complete heart block within the next few weeks or months. For this reason, pacemakers are often recommended for these patients.
2) When bundle branch block is associated with syncope (loss of consciousness).
➡ When a person with BBB – especially Left BBB – experiences syncope, that person may have an increased risk of developing complete heart block. A permanent pacemaker eliminates the problem.
If you’ve been told you have Right or Left Bundle Branch Block your doctor should perform his/her evaluation by looking for the kinds of underlying heart or lung diseases that have been associated with BBB.
If your heart and lungs are normal and you have RBBB, you can stop worrying.
While LBBB can also be seen in people whose hearts otherwise “seem” entirely normal, most often it indicates underlying heart disease.
So if you have LBBB, you should make especially sure your doctor has done a thorough cardiac evaluation.
Unless you’ve had a recent heart attack, or have had syncope, or have heart failure, the presence of BBB generally requires no specific treatment – beyond performing that thorough cardiac evaluation.
If you have significant heart failure, Bundle Branch Block can cause your heart to work less efficiently and can produce a worsening of your symptoms.
Anyone with both heart failure and BBB should discuss the potential need of a pacemaker with their doctor.