Right bundle branch block

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Right bundle branch block (RBBB) results from a defect in the heart’s electrical conduction system. There is a delay in failure of transmission of electrical impulses down the right bundle of the heart. As a result, the right ventricle depolarizes by an alternate mechanism. This is by means of cell-to-cell conduction. These cell to cell conduction impulses spread more slowly than usual from the interventricular septum to the left ventricle and to the right ventricle. This delay in conduction results in the characteristic ECG pattern which is a wide and notched QRS. Although conduction down the right bundle is delayed, conduction down the left bundle is normal. As a result, the interventricular septum and left ventricle depolarize in the normal fashion.

Prevalence of RBBB increases with age.

Right bundle branch block is associated with a persistently split second heart sound with normal respiratory variation in the splitting interval.

If there is a history of blunt trauma or any symptoms to suggest polymyositis, then troponin, creatine kinase (CK) and an echocardiogram should be obtained.

Criteria for complete right bundle branch block include: a QRS duration of > .12 seconds, an rSR’ pattern with a wide terminal R wave in V1 and a qRS complex with a wide S wave in V6.

In general treatment for right bundle branch block is not necessary. These patients need not limit their activity. However, if the RBBB progresses to heart block, the patient may be at risk for adverse clinical outcomes. In these patients further electrophysiologic testing may be necessary. Those patients who develop right bundle branch block after surgery should undergo EKG testing each year to evaluate for interval changes. In particular, care should be taken to observe for the development of sinus bradycardia supraventricular or ventricular ectopy.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2]; Raviteja Guddeti, M.B.B.S. [3]

Three types of RBBB have been identified based upon electrophysiologic studies.

In each of the three types of RBBB, the surface ECG pattern remains the same.

1. Proximal, or central, RBBB: This type of conduction defect occurs when the conduction block is located just distal to the bundle of His in the superior aspect of the right bundle branch. This type of block occurs when the proximal bundle is injured during surgery for an inlet or membranous ventricular septal defect (VSD).

2. Interruption between the proximal and distal aspects of the right bundle branch: This type of right bundle branch block occurs when the impulse is interrupted between the proximal and distal aspects of the right bundle branch. This type of bright bundle branch block is most commonly observed after surgical division of the moderator band.

3. Distal RBBB: This form is observed when distal ramifications of the right bundle are disrupted during right ventriculotomy or resection of muscle bundles in the right ventricular outflow tract.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2], Raviteja Guddeti, M.B.B.S. [3]

1. The normal cardiac conduction proceeds in a way so as to allow time for the atrium to relax during atrial diastole.
2. The electrical impulse generated in the SA node travels through the internodal pathways towards the AV node.
3. The conduction through the AV node is slowed down as it travels through the node. This decrease in velocity of conduction allows time for the atrium to contract ahead of the ventricle so that the blood from the atria can fill up the ventricles through the atrio-ventricular valves.
4. As the impulse flows through the compact AV node, it rapidly conducts through the ventricular myocardial cells. Once the depolarization is complete, the ventricle relaxes during diastole in preparation for the next impulse.

• The conduction system of the heart consists of specialized cells designed to conduct electrical impulse faster than the surrounding myocardial cells.
• Anatomically, the AV node is divided into three regions as follows:
  • Transitional cell zone: This is the region where the internodal atrial pathways merge with the compact AV node.
  • Compact AV node: This region is located at the apex of the triangle of Koch, which is formed by the ostium of coronary sinus, tricuspid annulus and the tendon of Todaro.
  • Penetrating portion of the AV bundle: This region enters the tendon of Todaro and runs within the fibrous body of the membranous interventricular septum and eventually divides at the crest of the muscular interventricular septum into right and left branches.
• The right bundle branch is the direct continuation of the penetrating bundle of His. It continues along the surface of the right side of the interventricular septum, below the papillary muscle of conus. It then proceeds towards the apex and passes through the moderator band to the base of the anterior papillary muscle and then to the free wall of the right ventricle.

• Right bundle branch block occurs when the electrical impulse is not conducted along the right bundle branch.
• As the conduction along the left bundle branch remains unaffected, the electrical impulse travels normally within the septum from left to right.
• However, the right ventricular contraction occurs comparatively slowly giving the characteristic ‘M’ pattern on the electrocardiogram.

• Familial cases of right bundle branch block have been observed in 4 Lebanese families and the abnormality was mapped to chromosome 19.
• There is a subset of patients with Brugada syndrome who have mutations in SCN5A, the gene encoding for the voltage-gated cardiac sodium channel.

• Duchenne muscular dystrophy
• Myotonic dystrophy: Other EKG findings include first-degree AV block, left anterior fascicular block, and intraventricular conduction delay. Patients may have arrhythmias and/or Stokes-Adams attacks.
• Kearns-Sayre Syndrome
• Brugada syndrome

Brugada syndrome: This syndrome is due to a channelopathy mediated by the SCN5A gene. It is important to note that the RBBB pattern seen in patients with this syndrome is not actually RBBB but is instead due to a repolarization abnormality. It is for this reason that the RBBB like pattern in Brugada syndrome is referred to as a ‘pseudo right bundle branch block.’ In this syndrome, the EKG shows ST-segment elevation in leads V1-V3. Cocaine consumption and / or the use of the antiarrhythmic propafenone may unmask the EKG findings of Brugada syndrome^[1].

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Raviteja Guddeti, M.B.B.S. [3]; Aarti Narayan, M.B.B.S [4]; Ayokunle Olubaniyi, M.B,B.S [5]

Right bundle branch block can result from various causes which include: cardiovascular (e.g. Atrial septal defect, cardiomyopathy, coronary artery disease, Ebstein anomaly); iatrogenic (e.g. Cardiac catheterization, cardiac transplantation, post cardiac surgery); infectious (e.g. Chagas disease, HIV, infective endocarditis, Lyme disease); pulmonary (e.g. COPD, cor pulmonale , pulmonary embolism, pulmonary hypertension), and many other disease conditions.

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Citalopram toxicity
• Cocaine abuse
• Heart failure
• Hyperkalemia
• Myocardial infarction
• Pulmonary embolism

• Cocaine abuse
• COPD
• Cor pulmonale
• Coronary heart disease
• Heart failure
• Hyperkalemia
• Hypertension
• Myocarditis
• Pulmonary embolism

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S. [2]; Aarti Narayan, M.B.B.S [3]

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Right bundle branch block should be differentiated from the following;

• Left bundle branch block:

The criteria to diagnose a left bundle branch block on an electrocardiogram includes the following:

1. The heart rhythm must be supraventricular in origin. A wide QRS complex that is not preceded by P waves would not qualify.
2. The QRS duration must be greater than or equal to 120 milliseconds.
3. There should be a QS or rS complex in lead V1.
4. There should be a monophasic R wave in lead I and lead V6.

The T wave deflection should be opposite of the terminal deflection of the QRS complex. This lack of concordance in direction is known as appropriate T wave discordance, and it is expected in patients with a left bundle branch block. A concordant T wave may suggest the presence of either ischemia ormyocardial infarction.

• Brugada syndrome:

Type 1 Brugada pattern is characterized by ST elevations in leads V₁-V₃ with a right bundle branch block (RBBB) like pattern, although it is actually a cause of “pseudo right bundle branch block” as electrocardiographically right bundle branch block is not actually present. Aprolongation of the PR interval is also frequently seen.

• Ventricular tachycardia:

Ventricular tachycardia and accelerated idioventricular rhythm can give rise to EKG patterns that mimic right bundle branch block. QRS complex will be wide and can have the appearance of a right bundle branch block, if the dominant rhythm originates from a pacemaker in the ventricle.

• Cardiac pacing:

Biventricular pacing can result in QRS complexes that sometimes resemble RBBB. However the presence of pacemaker spikes at the beginning of the QRS complexes can differentiate a paced rhythm from a right bundle branch complex.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Raviteja Guddeti, M.B.B.S. [3]; Aarti Narayan, M.B.B.S [4]

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Prevalence of right bundle branch block increases with age.

Prevalence of right bundle branch block without underlying heart disease ranges between 200 and 1300 per 100,000.

Increasing age is a significant predictor of newly acquired complete right bundle branch block and incomplete right bundle branch block.

Right bundle branch block and incomplete right bundle branch block are two to three times more common in men than in women (Copenhagen City Heart Study)^[1].

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S. [2]; Aarti Narayan, M.B.B.S [3]

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Significantly identified risk factors or predictors of a newly acquired complete right bundle branch block include (Copenhagen City Heart Study):^[1]

• Advancing age
• Male gender
• High systolic blood pressure

Similarly for incomplete right bundle branch block significant risk factors include:

• Advancing age
• Male gender
• Low BMI (body mass index)

Surgical repair of congenital heart diseases in children can be a potential risk for the occurrence of RBBB in children.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Aarti Narayan, M.B.B.S [3]; Raviteja Guddeti, M.B.B.S. [4]

Right bundle branch block may progress to complete heart block and sudden death if it is accompanied by higher grades of injuries to the conduction system, like first degree AV block and injury to the His-Purkinje system leading to a left anterior hemiblock.

In general, the natural history of right bundle branch block is benign. If right bundle branch block is due to surgery then there are generally no acute hemodynamic consequences. The subsequent courses also quite benign. An exception is if there is substantial injury to the His-Purkinje system in which case left anterior hemiblock or first-degree AV block may be present.

There are familial cases of right bundle branch block, which are benign.

Complication rate is higher in patients who have myocardial infarction and develop a new RBBB compared to those who have heart attack and not develop a new RBBB.

• Ventricular arrhythmias
• Sudden cardiac death
• RBBB can delay the accurate diagnosis of heart attack

• Isolated right bundle branch block without underlying heart disease has an excellent prognosis.
• In the presence of a known underlying heart disease, especially coronary artery disease, complete RBBB is associated with increased mortality.
• RBBB in the setting of acute myocardial infarction is associated with increased mortality even after the initiation of thrombolytic therapy.
• Studies have shown that RBBB is associated with worse outcomes in the long run in patients with established heart failure.
• Patients who have type II second degree atrioventricular block or multi-fascicular block along with RBBB have a poor prognosis compared to those without RBBB and such patients are also known to have a more significant myocardial disease.
• The Copenhagen City Heart Study showed that RBBB is associated with a significant increase in all-cause and cardiovascular mortality in both genders^[1].
• There are three scenarios in which right bundle branch block can be associated with poor prognosis:

1. Brugada syndrome: If right bundle branch block is present, then sudden death may occur.
2. Kearns Sayre syndrome: Again, if right bundle branch block is present then sudden death may occur.
3. Tetralogy of Fallot: If right bundle branch block is present with a markedly prolonged QRS (> 180 ms), then the patient may be at risk for ventricular arrhythmias and sudden death.
4. Arrhythmogenic right ventricular cardiomyopathy: Risk of sudden death is higher.

• In children, surgically induced RBBB has a benign course in the long run, however rarely if RBBB is associated with injury to the His-Purkinje system, it is associated with progression to complete heart block and sudden death. Children who have undergone surgery for repair of tetralogy of Fallot are at increased risk for ventricular arrhythmias and sudden death.

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