Table of ContentsView AllTable of ContentsHeart’s Electrical SystemTypes of Bundle Branch BlockSymptomsCauses and Risk FactorsDiagnosisTreatment
Table of ContentsView All
View All
Table of Contents
Heart’s Electrical System
Types of Bundle Branch Block
Symptoms
Causes and Risk Factors
Diagnosis
Treatment
Verywell / Gary Ferster
The Heart’s Electrical System
The right and left bundle branches distribute the electrical impulse from the bundle of His across the right and left ventricles, causing them to beat. When the bundle branches are functioning normally, the right and left ventricles contract regularly and nearly simultaneously. This is described asnormal sinus rhythm.
Normal Sinus Rhythm of the Heart
If you have a bundle branch block, either the left bundle branch or the right bundle branch (or both) isn’t functioning as it should. This leads to a disruption of heart rhythm as it pumps.
Note that while the term bundle branch “block” is used, the affected bundle branch may or may not be fully “blocked.” In many cases, the bundle branch is notcompletelyblocked, but instead is simply conducting the electrical impulse more slowly than normal.
The chief effect of a bundle branch block is that it interferes with the coordinated contraction of the left and right ventricles. The contraction of one ventricle—the one that has a “blocked” bundle branch—occursslightlyafter the contraction of the other, rather than at the same time.
Left Bundle Branch Block
The left side of the heart receives oxygenated blood into the left atrium from the lungs. This blood flows from the left atrium into the left ventricle, which contracts powerfully, sending oxygenated blood to the body.
A left bundle branch block interferes with the contraction of the left ventricle.
Right Bundle Branch Block
The right side of the heart receives deoxygenated blood from the body’s circulation into the right atrium and sends this blood to the right ventricle, and then to the lungs to be replenished with oxygen.
The contraction of the right ventricle is normally slightly less powerful than the contraction of the left ventricle. A right bundle branch block disrupts the contraction of the right ventricle.
In most cases, bundle branch block does not produce symptoms, so you might not know that you have this problem unless you have cardiac tests. However, it can cause intermittent effects, including dizziness and even syncope (fainting).
Such symptoms are more likely to occur if the bundle branch block exists along with a cardiovascular disease such ashypertension (high blood pressure),heart failure, or cardiomyopathy (disease of the heart muscle).
Symptoms are also more common if the bundle branch block is severe or involves both the right and left bundle branches.
Possible effects of a bundle branch block:
With a very severe bundle branch block, the electrical impulse may suddenly stop reaching the ventricles altogether, leading to a completeheart block—which can produce syncope or sudden cardiac death.
Certain factors can increase the chances of bundle branch block, but the condition can occur without an identifiable cause, especially on the right side. Typically, when there is not an identifiable cause, the health effects of the bundle branch block are less significant and might even be completely negligible.
The most common cardiac conditions associated with bundle branch block include:
Right bundle branch block can develop due to all of these causes, and it can also occur as a result of a lung disease, including:
Identifying a bundle branch block relies on diagnostic testing that includes a 12-lead ECG and an echocardiogram. An ECG is a non-invasive test that uses electrodes placed on the surface of the chest to detect heart rhythm. An echocardiogram is a non-invasive ultrasound that visualizes the heart as it beats, potentially detecting disruptions in rhythm.
In many cases, one test alone will show the pattern consistent with bundle branch block, both tests won’t be necessary.
Bundle Branch Block and ECG
An ECG is a visual representation of an electrical impulse as it moves through the heart. A computer-generated wave pattern reflecting the rhythm of the heart is produced based on electrical impulses detected with small metal electrodes placed on the chest.
In the figure above,Panel Ashows what a normal QRS complex looks like on a normal ECG. Since both ventricles normally receive the electrical impulse at the same time, the normal QRS complex is relatively narrow (generally less than 0.1 second in duration.) The simultaneous stimulation of both ventricles depends on the electrical impulse traveling down both the right and left bundle branches at nearly the same rate of speed.
With a bundle branch block, it takes longer for the electrical signal to be completely distributed across both ventricles and the QRS complex widens.
Sometimes, both bundle branches are affected, and the bundle branch block pattern on the ECG is not clearly identifiable as either right or left bundle branch block. In this case, the bundle branch block is referred to as an “intraventricular conduction delay.”
Echocardiogram
A bundle branch block might be detected with an echocardiogram. This non-invasive test allows healthcare providers to visualize the motion and rhythm of the heart as it beats.
Although the movement and rhythm of the heart can be altered with a bundle branch block, an echocardiogram may not pinpoint the bundle branch block as the cause of these abnormalities.
More importantly, this test gives healthcare providers a detailed view of the heart. It can be used to help identify anatomical defects that are associated with a worse prognosis of bundle branch block.
If you have a bundle branch block, your healthcare provider might order an echocardiogram for you so your medical team will be better able to assess the impact of your conduction disorder.
Cardiac Evaluation
Depending on your symptoms and risk factors, you might need more testing to evaluate your heart and/or lungs, although this isn’t necessarily part of the evaluation of an uncomplicated bundle branch block without symptoms or risk factors. For example, you may need to have a diagnosticcardiac catheterizationto evaluate the blood vessels in your heart or astress testif you are having angina (chest pain).
Occasionally, a severe bundle branch block may require the surgical placement of apacemakerto prevent episodes of complete heart block.
Associated Conditions
Also, if you have another type of heart disease along with your conduction block, the associated heart condition typically needs to be treated.
This might involve approaches like prescription blood thinners for CAD, antihypertensive medication to alleviate high blood pressure, bronchodilators to treat COPD, or surgical repair for a malfunctioning heart valve.
A Word From Verywell
Bundle branch block is not an uncommon incidental finding on an ECG. People who have a bundle branch block have a higher risk of some medical issues, especially with heart surgery. You are unlikely to know that you have a bundle branch block unless you have a cardiac evaluation for another reason (such as a pre-operative test or to look for heart disease). While sometimes bundle branch block itself causes cardiac issues, in most cases it does not pose a significant problem.
10 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Heart Association.Conduction disorders.Ferri FF, ed.Ferri’s Clinical Advisor 2022. Philadelphia, PA: Elsevier.Scherbak D, Hicks GJ.Left bundle branch block (LBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.Nazif TM, Chen S, George I, et al.New-onset left bundle branch block after transcatheter aortic valve replacement is associated with adverse long-term clinical outcomes in intermediate-risk patients: an analysis from the PARTNER II trial.Eur Heart J. 2019;40(27):2218-2227. doi:10.1093/eurheartj/ehz227Abdurrazzak A. Gehani, Fahad Alkindi, Jassim Al Suwaidi, Abdulrahman Arabi, Awad Alqahtani, Ihsan Rafie, Rajvir Singh, Hajar Albinali.Is right bundle branch block more powerful predictor of in-hospital mortality than left bundle branch block? Analysis from the cardiology registry.J Am Coll Cardiol.2015 Mar, 65 (10 Supplement) A175.doi:10.1016/S0735-1097(15)60175-9Tovia-Brodie O, Letourneau-Shesaf S, Hochstadt A, et al.The utility of prophylactic pacemaker implantation in right bundle branch block patients pre-transcatheter aortic valve implantation.Isr Med Assoc J. 2019;12(21):790-795.Harkness WT, Hicks M.Right bundle branch block (RBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507872/Lépori AJ, Mishima RS, Rodriguez G, et al.Relationship between electrocardiographic characteristics of left bundle branch block and echocardiographic findings.Cardiol J. 2015;22(4):397-403. doi:10.5603/CJ.a2015.0005Ferrara MG, Cappucci RV, Wang DY.Chest pain resolution with His-bundle pacing in a patient with left bundle branch block-related nonischemic left ventricular dysfunction.J Innov Card Rhythm Manag. 2019;10(9):3810-3814. doi:10.19102/icrm.2019.100906Tan NY, Witt CM, Oh JK, Cha YM.Left bundle branch block: Current and future perspectives.Circ Arrhythm Electrophysiol.2020;13(4):e008239.doi:10.1161/CIRCEP.119.008239
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Heart Association.Conduction disorders.Ferri FF, ed.Ferri’s Clinical Advisor 2022. Philadelphia, PA: Elsevier.Scherbak D, Hicks GJ.Left bundle branch block (LBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.Nazif TM, Chen S, George I, et al.New-onset left bundle branch block after transcatheter aortic valve replacement is associated with adverse long-term clinical outcomes in intermediate-risk patients: an analysis from the PARTNER II trial.Eur Heart J. 2019;40(27):2218-2227. doi:10.1093/eurheartj/ehz227Abdurrazzak A. Gehani, Fahad Alkindi, Jassim Al Suwaidi, Abdulrahman Arabi, Awad Alqahtani, Ihsan Rafie, Rajvir Singh, Hajar Albinali.Is right bundle branch block more powerful predictor of in-hospital mortality than left bundle branch block? Analysis from the cardiology registry.J Am Coll Cardiol.2015 Mar, 65 (10 Supplement) A175.doi:10.1016/S0735-1097(15)60175-9Tovia-Brodie O, Letourneau-Shesaf S, Hochstadt A, et al.The utility of prophylactic pacemaker implantation in right bundle branch block patients pre-transcatheter aortic valve implantation.Isr Med Assoc J. 2019;12(21):790-795.Harkness WT, Hicks M.Right bundle branch block (RBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507872/Lépori AJ, Mishima RS, Rodriguez G, et al.Relationship between electrocardiographic characteristics of left bundle branch block and echocardiographic findings.Cardiol J. 2015;22(4):397-403. doi:10.5603/CJ.a2015.0005Ferrara MG, Cappucci RV, Wang DY.Chest pain resolution with His-bundle pacing in a patient with left bundle branch block-related nonischemic left ventricular dysfunction.J Innov Card Rhythm Manag. 2019;10(9):3810-3814. doi:10.19102/icrm.2019.100906Tan NY, Witt CM, Oh JK, Cha YM.Left bundle branch block: Current and future perspectives.Circ Arrhythm Electrophysiol.2020;13(4):e008239.doi:10.1161/CIRCEP.119.008239
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Heart Association.Conduction disorders.Ferri FF, ed.Ferri’s Clinical Advisor 2022. Philadelphia, PA: Elsevier.Scherbak D, Hicks GJ.Left bundle branch block (LBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.Nazif TM, Chen S, George I, et al.New-onset left bundle branch block after transcatheter aortic valve replacement is associated with adverse long-term clinical outcomes in intermediate-risk patients: an analysis from the PARTNER II trial.Eur Heart J. 2019;40(27):2218-2227. doi:10.1093/eurheartj/ehz227Abdurrazzak A. Gehani, Fahad Alkindi, Jassim Al Suwaidi, Abdulrahman Arabi, Awad Alqahtani, Ihsan Rafie, Rajvir Singh, Hajar Albinali.Is right bundle branch block more powerful predictor of in-hospital mortality than left bundle branch block? Analysis from the cardiology registry.J Am Coll Cardiol.2015 Mar, 65 (10 Supplement) A175.doi:10.1016/S0735-1097(15)60175-9Tovia-Brodie O, Letourneau-Shesaf S, Hochstadt A, et al.The utility of prophylactic pacemaker implantation in right bundle branch block patients pre-transcatheter aortic valve implantation.Isr Med Assoc J. 2019;12(21):790-795.Harkness WT, Hicks M.Right bundle branch block (RBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507872/Lépori AJ, Mishima RS, Rodriguez G, et al.Relationship between electrocardiographic characteristics of left bundle branch block and echocardiographic findings.Cardiol J. 2015;22(4):397-403. doi:10.5603/CJ.a2015.0005Ferrara MG, Cappucci RV, Wang DY.Chest pain resolution with His-bundle pacing in a patient with left bundle branch block-related nonischemic left ventricular dysfunction.J Innov Card Rhythm Manag. 2019;10(9):3810-3814. doi:10.19102/icrm.2019.100906Tan NY, Witt CM, Oh JK, Cha YM.Left bundle branch block: Current and future perspectives.Circ Arrhythm Electrophysiol.2020;13(4):e008239.doi:10.1161/CIRCEP.119.008239
American Heart Association.Conduction disorders.
Ferri FF, ed.Ferri’s Clinical Advisor 2022. Philadelphia, PA: Elsevier.
Scherbak D, Hicks GJ.Left bundle branch block (LBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.
Nazif TM, Chen S, George I, et al.New-onset left bundle branch block after transcatheter aortic valve replacement is associated with adverse long-term clinical outcomes in intermediate-risk patients: an analysis from the PARTNER II trial.Eur Heart J. 2019;40(27):2218-2227. doi:10.1093/eurheartj/ehz227
Abdurrazzak A. Gehani, Fahad Alkindi, Jassim Al Suwaidi, Abdulrahman Arabi, Awad Alqahtani, Ihsan Rafie, Rajvir Singh, Hajar Albinali.Is right bundle branch block more powerful predictor of in-hospital mortality than left bundle branch block? Analysis from the cardiology registry.J Am Coll Cardiol.2015 Mar, 65 (10 Supplement) A175.doi:10.1016/S0735-1097(15)60175-9
Tovia-Brodie O, Letourneau-Shesaf S, Hochstadt A, et al.The utility of prophylactic pacemaker implantation in right bundle branch block patients pre-transcatheter aortic valve implantation.Isr Med Assoc J. 2019;12(21):790-795.
Harkness WT, Hicks M.Right bundle branch block (RBBB). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507872/
Lépori AJ, Mishima RS, Rodriguez G, et al.Relationship between electrocardiographic characteristics of left bundle branch block and echocardiographic findings.Cardiol J. 2015;22(4):397-403. doi:10.5603/CJ.a2015.0005
Ferrara MG, Cappucci RV, Wang DY.Chest pain resolution with His-bundle pacing in a patient with left bundle branch block-related nonischemic left ventricular dysfunction.J Innov Card Rhythm Manag. 2019;10(9):3810-3814. doi:10.19102/icrm.2019.100906
Tan NY, Witt CM, Oh JK, Cha YM.Left bundle branch block: Current and future perspectives.Circ Arrhythm Electrophysiol.2020;13(4):e008239.doi:10.1161/CIRCEP.119.008239
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