Right bundle branch block
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| 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. |
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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]
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 or 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.
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.
Associated syndromes
- 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.
Pseudo Right Bundle Branch Block
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 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
- 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
- Acute pulmonary embolism
- Atrial septal defect
- Cardiomyopathy
- Cor Pulmonale
- Coronary Heart Disease
- Lenegre's Disease
- Lev's Disease
- Myocardial Infarction
- Myocarditis
Epidemiology and Demographics
Age
The prevalence of RBBB increases with age.
Natural History, Complications and Prognosis
In general, the natural history of right bundle branch block benign. Right bundle branch block can be associated with poor prognosis in the following scenarios:
- 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 are also 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. Pulmonary arterial line placement [1] in a patient with LBBB can result in a complete heart block if the right bundle branch is traumatized during the process.
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.
Electrocardiogram
- 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.
- 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.
- 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.
Shown below is an EKG depicting the main characteristics of right bundle branch block on lead V1.
Copyleft images obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:RBBB.png
EKG Examples
Shown below is an EKG with left axis deviation with rSR' pattern (M pattern) in leads V1 and V2 depicting a right bundle branch block. The EKG shows sinus rhythm. There are wide QRS complexes (>120ms) throughout the precordium. There are small R waves in the inferior leads.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E22.jpg
Shown below is an EKG from an elderly woman who had previously undergone surgery for recurrent ventricular tachycardia. She was being treated with Tambacor and metoprolol. The EKG shows sinus rhythm with an sRS' pattern seen in leads I, V2, and V3 and a wide QRS of 159ms consistent with a RBBB. There is also a right axis deviation suggesting a right posterior hemi-block. The poor R wave progression suggests previous anterior MI.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E29.jpg
Shown below is an EKG 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. There is an RSR' pattern in lead V1 depicting a right bundle branch block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E342.jpg
Shown below is an EKG with an rsr' pattern in leads V1, V2, and V3 depicting a right bundle branch block with left axis deviation.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:ECG_RBTB_LAtrD.jpg
Shown below is an EKG with an RSR' pattern in leads V2 and V3 depicting a right bundle branch block with left axis deviation.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an RSR' pattern in leads V1, V2, V3, and aVR depicting a right bundle branch block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rSR' pattern in leads III, aVR, aVF, V1, V2, and V3 depicting a right bundle branch block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an RSR' pattern in leads V1 and V2, and a qRs pattern in V6. There is slurring of the S wave in leads I and V6. All these patterns suggest right bundle branch block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rSR' pattern in leads III and V1. There is slurring of the S wave in leads I and V6. These findings are consistent with right bundle branch block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an RSR' pattern in lead V1, an RSr' pattern in lead V2, and wide QRS complexes in leads V1 and V2 depicting a right bundle branch block. There is also PR prolongation which is constant indicating first degree heart block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an RSR' pattern in leads V1 and V2 indicating a right bundle branch block. Tall P waves seen in leads II and III indicate right atrial enlargement.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an RSR' pattern in lead V2 suggesting right bundle branch block. There is ST elevation in the precordial leads suggesting STEMI. Heart rate is less than 60 suggesting bradycardia. There is left axis deviation. In addition, there is PR prolongation which is constant suggesting first degree heart block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:RBBB_inf_MI_V4R.jpg
Shown below is an EKG with an RSR' pattern in leads V1, V2, V3, V4, aVF, and III suggesting right bundle branch block. There is left axis deviation. In addition, the PR interval is prolonged and constant suggesting first degree heart block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:RBBB_inf_MI_baseline.jpg
Shown below is an EKG with an rsR' pattern in leads V1 and V2 suggesting right bundle branch block. The EKG also shows supraventricular tachycardia.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rsR' pattern in leads III and V1, and qR' pattern in leads V2 and V3 suggesting right bundle branch block. The EKG also shows an old anterior MI.
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Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rsR' pattern in leads III, aVR and V1 suggesting right bundle branch block. The EKG also shows an old inferior MI, anterior MI, and LAFB.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rsR' pattern in lead V1 suggesting right bundle branch block. The EKG also shows an old inferior MI.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rsR' pattern in lead V1 suggesting RBBB and there is a left axis deviation suggesting LAFB.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rsR' pattern in lead V1 suggesting RBBB and there is a left axis deviation suggesting LAFB. In addition, the PR interval is prolonged and constant suggesting first degree heart block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with an rsR' pattern in lead V1, V2, and V3 suggesting RBBB. The EKG also shows a left axis deviation suggesting LAFB.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG with a slurred S wave in leads III, aVR, aVF, V1, and V2 suggesting RBBB. The EKG also shows a left axis deviation suggesting LAFB.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an EKG depicting atrial fibrillation with a controlled ventricular rate. The QRS is wide (>120ms) and has a tall R' in V1 and an S wave in V6. There is a left axis deviation. The cardiogram suggests a right bundle branch block and a left anterior hemiblock. The patient has a cardiomyopathy with an ejection fraction of 20%.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E243.jpg
Shown below is an EKG depicting sinus rhythm with a normal PR interval and a prolonged QRS interval (>120ms). There is a conduction abnormality best described as a right bundle branch block due to the rsR' wave in V1. Note the S wave in V6 which is due to the RBBB is smaller than the R wave in V6. The axis of the QRS is difficult to determine, but one usually looks at the first 60 ms. (1 1/2 small squares) to determine the axis with a RBBB. If the axis of the first 60 ms. of the QRS is more than 90 degrees and there is an rS in lead I and a Q in lead III then one would consider a left posterior fascicular block. This is not the case here.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E196.jpg
Treatment
In general, treatment for right bundle branch block is not necessary. These patients need not limit their activity. However, if the RBBB progresses to complete 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 ectopy, or ventricular ectopy.
Related Chapters
References
- ↑ Morris D, Mulvihill D, Lew WY (1987). "Risk of developing complete heart block during bedside pulmonary artery catheterization in patients with left bundle-branch block". Archives of Internal Medicine. 147 (11): 2005–10. PMID 3675104. Retrieved 2012-10-17. Unknown parameter
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