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==Pathophysiology==
==Pathophysiology==
Three types of [[RBBB]] have been identified based upon electrophysiologic studies.
===Normal Conduction===
# The normal cardiac conduction proceeds in a way so as to allow time for the [[atrium]] to relax during atrial [[diastole]].
# The electrical impulse generated in the [[SA node]] travels through the internodal pathways towards the [[AV node]].
# 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.
# 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.


In  each of the three types of RBBB, the surface ECG pattern remains the same.
[[Image:Conduction system of the heart.png|left|thumb|200px|Conduction system of the heart]]<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />


1. Proximal, or central, RBBB:
===Anatomy===
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]]).  
* 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 [[interventricular septum|membranous interventricular septum]] and eventually divides at the crest of the [[interventricular septum|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|papillary muscle of conus]]. It then proceeds towards the apex and passes through the [[moderator band]] to the base of the [[papillary muscle|anterior papillary muscle]] and then to the free wall of the [[right ventricle]].


2. Interruption between the proximal and distal aspects of the right bundle branch:
[[Image:AV node.png|left|thumb|500px|Structure of the heart's conduction system]]<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
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:
===Pathophysiology===
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.
* 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.


===Genetics===
===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.
* 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.
* 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===
===Associated Syndromes===
*[[Duchenne muscular dystrophy]]
*[[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]].
*[[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]]
*[[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]].
*[[Brugada syndrome]]


===Pseudo Right Bundle Branch Block===
===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]].
[[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]]<ref name="pmid23613002">{{cite journal |author=Yildiz BS, Gungor H, Gul I, Bilgin M, Zoghi M, Akilli A |title=Is a drug-challenge test with propafenone adequate to exclude Brugada syndrome? |journal=Cardiovascular Journal of Africa |volume=24 |issue=2 |pages=e4–6 |year=2013 |pmid=23613002 |doi=10.5830/CVJA-2012-068 |url=}}</ref>.


==References==
==References==
{{Reflist|2}}
{{Reflist|2}}
[[Category:Needs overview]]
[[Category:Needs overview]]
[[Category:Needs content]]
[[Category:Electrophysiology]]
[[Category:Electrophysiology]]
[[Category:Disease]]
[[Category:Disease]]

Latest revision as of 02:13, 29 April 2013

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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]

Pathophysiology

Normal Conduction

  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.
Conduction system of the heart




















Anatomy

  • 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:
  • 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.
Structure of the heart's conduction system

















Pathophysiology

  • 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.

Genetics

  • 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.

Associated Syndromes

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 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].

References

  1. Yildiz BS, Gungor H, Gul I, Bilgin M, Zoghi M, Akilli A (2013). "Is a drug-challenge test with propafenone adequate to exclude Brugada syndrome?". Cardiovascular Journal of Africa. 24 (2): e4–6. doi:10.5830/CVJA-2012-068. PMID 23613002.

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