Right bundle branch block

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	Right bundle branch block;
	ECG characteristics of a typical RBBB showing wide QRS complexes with a terminal R wave in lead V1 and slurred S wave in lead V6.
ICD-10	I45.1
DiseasesDB	11620

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

Synonyms and keywords: RBBB

Overview

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 result, the interventricular septum and left ventricle depolarize in the normal fashion.

Pathophysiology

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.

Genetics

There can be familial cases of right bundle branch block such as that 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.

Associated syndromes

Duchenne muscular dystrophy

Myotonic dystrophy Other ECG 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: 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. In this syndrome, the ECG shows ST-segment elevation in leads V1-V3. Cocaine consumption and / or the use of the antiarrhythmic propafenone may unmask the ECG findings of Brugada syndrome.

Causes of Right Bundle Branch Block

Surgery for correction of congenital heart disease is the most common cause of RBBB among children any United States. This includes surgery for repair of an isolated VSD or another congenital heart disease that includes a VSD (eg, double-chambered right ventricle, AV canal defect, or tetralogy of Fallot). The incidence of RBBB varies and ranges from 25-81% after repair of a VSD to 60-100% after repair of tetralogy of Fallot. The risk of RBBB after surgery varies depending upon the proximity of the VSD to the His-Purkinje system.
Blunt trauma
Polymyositis
Premature atrial contractions or supraventricular tachycardia may cause a transient form up right bundle branch block. This occurs when a premature impulse is conducted from the AV node to the His bundle while the right bundle branch remains in its refractory period, but the left bundle is not. As a result, conduction down the right bundle branch is delayed or blocked.
Prenatal exposure to each one HIV type 1 may cause right anterior hemiblock.
Familial

Differential Diagnosis

Epidemiology and Demographics

Age

The prevalence of RBBB increases with age.

Natural Hisstory

In general, the natural history of right bundle branch block benign. There are three scenarios in which right bundle branch block can be associated with poor prognosis:

Brugada syndrome: if right bundle branch block is present, then sudden death may occur.
Kearns Sayre syndrome: again, if right bundle branch block is present than sudden death may occur.
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.

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.

Diagnosis

Physical Examination

Heart

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

Laboratory Findings

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.

ECG

The heart rhythm must be supraventricular in origin
The QRS axis can be either normal, or right or left axis deviation may be present.
The QRS duration must be = or > 120 ms
- For complete RBBB, the patient's age must be taken into account to determine if the duration of the QRS complex is prolonged for the patient's age.
  - Maximum QRS durations are 0.07 s for newborns <6 days, 0.08 s for patients aged 1 week to 7 years, and 0.09 s for patients aged 7-15 years.
There should be a terminal R wave in lead V1-V3R (e.g., R, rR', rsR', rSR' or qR')
- This pattern is present because the initial R wave represents septal activation, the S wave represents left ventricular activation, and the R' represents activation of the right ventricle from the septum and left ventricle.
There should be a slurred S wave in leads I and V6. This represent left ventricular activation.
- Because transmission of the electrical impulse through the left bundle is normal, this results in normal depolarization of the septum and the left ventricle. As a result, there is an initial R wave in lead I and V1 and the Q wave in V6.

The T wave should be deflected opposite the terminal deflection of the QRS complex. This is known as appropriate T wave discordance with bundle branch block. A concordant T wave may suggest ischemia or myocardial infarction.

Below is an electrocardiogram showing the main characteristics of right bundle branch block on lead V1.

The rhythm is sinus. The QRS is wide (>120ms.) and the axis is markedly negative. There are small R waves in the inferior leads. The recording shows a right bundle branch block and a left anterior fasicular block.

Animation of RBBB

EKG examples

EKG below is from an elderly woman who had previously undergone surgery for recurrent ventricular tachycardia. She was being treated with Tambacor and metoprolol. The cardiogram shows sinus rhythm with a wide QRS of 159ms consistent with a RBBB and a rightward axis suggesting right posterior hemi-block. The PR interval is slightly prolonged at 2121ms. The poor R wave progression seen best in lead V2 suggests previous anterior wall MI.

EKG below is a recording from an older man in the surgical intensive care unit. He was recovering from a motor vehicle accident where he sustained a chest injury from his seat belt. The rhythm is sinus rhythm with a prolonged p wave duration in lead III( >140ms) and a pronounced terminal negativity in V1 suggestive of left atrial abnormality. The QRS is wide with a duration of 137ms and a superior and right ward axis. There is an RSR in V1 and the S wave is greater than the R in V6. This is an unusual pattern for aberrance and is more in keeping with ventricular ectopy. In this case, this appears to be a right bundle branch block with a possible left posterior hemi-block.

Of note, in spite of this conduction disturbance the patient was able to sustain reentrant supraventricular tachycaridas requiring intravenous adenosine for termination.