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VisualWikitext

Latest revision as of 13:58, 8 June 2020

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Synonyms and keywords: BBB

For detailed medical information on Left Bundle Branch Block click here.

For detailed medical information on Right Bundle Branch Block click here.

Overview

A bundle branch block refers to a defect of the heart's electrical conduction system below the level of the AV node. Depending upon the level and location of the block/defect in the conducting pathway bundle branch block can be classified into left bundle branch block and right bundle branch block.

Physiology

Normal 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:
- 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 left bundle branch penetrates the membranous portion of the interventricular septum and divides into several smaller branches. Parts of the left bundle branch include a pre-divisional segment, anterior fascicle/hemibundle and posterior fascicle/hemibundle. Rarely a median fascicle is present in some hearts.
- The anterior fascicle supplies the anterior papillary muscle and the Purkinje network of the antero-lateral surface of the left ventricle.
- The posterior fascicle supplies the posterior papillary muscle and the Purkinje network of the postero-inferior surface of the left ventricle.
- Left bundle branch receives its blood supply from left anterior descending artery.

Structure of the heart's conduction system

Normal Physiology

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 it. 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.

Classification

Bundle Branch Block

Left Bundle Branch Block

Right Bundle Branch Block

Based on Duration

Based on Extent of Block

Proximal RBB

Intermediate RBB

Distal RBB

New LBB

Old LBB

LBB of unknown duration

Complete LBB

Incomplete LBB

Related Chapters

References

de:Schenkelblock

Template:WikiDoc Sources CME Category::Cardiology

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+{{CMG}} ; {{AE}} {{ADG}}
 {{SK}} BBB
-Please help WikiDoc by adding more content here.  It's easy!  Click  [[Help:How_to_Edit_a_Page|here]]  to learn about editing.
+'''For detailed medical information on Left Bundle Branch Block click [[Left bundle branch block|here]].'''
+'''For detailed medical information on Right Bundle Branch Block click [[Right bundle branch block|here]].'''
 ==Overview==
-A bundle branch block refers to a defect of the [[heart]]'s [[electrical conduction system of the heart|electrical conduction system]] below the level of the [[AV node]].
+A bundle branch block refers to a defect of the [[heart]]'s [[electrical conduction system of the heart|electrical conduction system]] below the level of the [[AV node]]. Depending upon the level and location of the block/defect in the conducting pathway bundle branch block can be classified into left bundle branch block and right bundle branch block.
+==Physiology==
+=== Normal 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:
+**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 left bundle branch penetrates the membranous portion of the interventricular septum and divides into several smaller branches. Parts of the left bundle branch include a pre-divisional segment, anterior fascicle/hemibundle and posterior fascicle/hemibundle. Rarely a median fascicle is present in some hearts.
+**The anterior fascicle supplies the anterior [[papillary muscle]] and the Purkinje network of the antero-lateral surface of the left ventricle.
+**The posterior fascicle supplies the posterior papillary muscle and the Purkinje network of the postero-inferior surface of the left ventricle.
+**Left bundle branch receives its blood supply from [[left anterior descending artery]].
-==Pathphysiology==
+[[Image:AV node.png|thumb|600x600px|Structure of the heart's conduction system|link=https://www.wikidoc.org/index.php/File:AV_node.png|center]]<br />
-:''Main article: [[Electrical conduction system of the heart]]''
-The heart's electrical activity normally starts in the [[sinoatrial node]] (the heart's natural [[cardiac pacemaker|pacemaker]]), which is situated on the upper right [[Atrium (heart)|atrium]]. From there the impulse travels to the left atrium and the [[atrioventricular node]]. From the AV node the electrical impulse travels down the [[Bundle of His]] and divides into the right and left bundle branches. The right bundle branch contains one fascicle. The left bundle branch subdivides into two fascicles: the left anterior fascicle and the left posterior fascicle. Ultimately, the fascicles divide into millions of Purkinje fibers which in turn interdigitize with individual cardiac myocytes, allowing for rapid, coordinated, and synchronous depolarization of the ventricles.
-When a bundle branch or fascicle becomes injured (due to underlying [[heart disease]], [[myocardial infarction]], or cardiac surgery), it may cease to conduct electrical impulses appropriately. This results in altered pathways for ventricular depolarization. Since the electrical impulse can no longer use the preferred pathway across the bundle branch, it may move instead through muscle fibers in a way that both slows the electrical movement and changes the direction of the impulses. As a result, there is a loss of ventricular synchrony, ventricular depolarization is prolonged, and there may be a corresponding drop in cardiac output. When [[heart failure]] is present, a [[artificial pacemaker|pacemaker]] may be used to resynchronize the ventricles.
+=== Normal Physiology ===
-==Diagnosis==
+*The normal cardiac conduction proceeds in a way so as to allow time for the [[atrium]] to relax during atrial [[diastole]].
-===Electrocardiogram===
+*The electrical impulse generated in the [[SA node]] travels through the internodal pathways towards the [[AV node]].
-A bundle branch block can be diagnosed when the duration of the QRS complex on the [[electrocardiogram|ECG]] exceeds 120 ms. A right bundle branch block typically causes prolongation of the last part of the QRS complex, and may shift the heart's electrical axis slightly to the right. The ECG will show a terminal R wave in lead V1 and a slurred S wave in lead I.
+*The conduction through the AV node is slowed down as it travels through it. 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.
-Left bundle branch block widens the entire QRS, and in most cases shifts the heart's electrical axis to the left. The ECG will show a QS or rS complex in lead V1 and a monophasic R wave in lead I. Another normal finding with bundle branch block is appropriate T wave discordance. In other words, the T wave will be deflected opposite the terminal deflection of the QRS complex.
+*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.
-==Treatment==
+<br />
-Many people with bundle branch blocks may still be quite active, and may have nothing more remarkable than an abnormal appearance to their ECG.  However, when bundle blocks are complex and diffuse in the bundle systems, or associated with additional and significant ventricular muscle damage, they may be a sign of serious underlying heart disease. In more severe cases, a [[Artificial pacemaker|pacemaker]] may be required to re-establish better heart muscle function.
+== Classification ==
+</small>
+{{Family tree/start}}
+{{Family tree | | | | | | | | | | | | | | | | | | | | | | | | | A01 | | | |A01= Bundle Branch Block}}
+{{Family tree | | | | | | | | | | | | | | | | | | | | | | | | | |!| | | | | }}
+{{Family tree | | | | | | | | | | | | | | | | | |,|-|-|-|-|-|-|-|^|-|-|-|-|-|-|-|-|-|-|-|-|.|}}
+{{Family tree | | | | | | | | | | | | | | | | | C01 | | | | | | | | | | | | | | | | | | | C02 |C01= Left Bundle Branch Block| C02= Right Bundle Branch Block}}
+{{Family tree | | | | | | | | | | | | | | | | | |!| | | | | | | | | | | | | | | | | | | | |!| | | }}
+{{Family tree | | | | | | | | |,|-|-|-|-|-|-|-|-|^|-|-|-|-|-|-|-|.| | | | | |,|-|-|-|-|-|-|+|-|-|-|-|-|-|.| |}}
+{{Family tree | | | | | | | | |!| | | | | | | | | | | | | | | | |!| | | | | |!| | | | | | |!| | | | | | |!| | }}
+{{Family tree | | | | | | | | D01 | | | | | | | | | | | | | | | D02 | | | | D03 | | | | | D04 | | | | | D05 | | |D01=Based on Duration| D02= Based on Extent of Block|D03=Proximal RBB|D04=Intermediate RBB|D05= Distal RBB}}
+{{Family tree | | | | | | | | |!| | | | | | | | | | | | | | | | |!| | | | | | | | | | | | | | | | | | | | | | }}
+{{Family tree | | |,|-|-|-|-|-|+|-|-|-|-|-|.| | | | | |,|-|-|-|-|^|-|-|-|-|.| | | | | | | | | | | |D01=Based on Duration| D02= Based on Extent of Block }}
+{{Family tree | | |!| | | | | |!| | | | | |!| | | | | |!| | | | | | | | | |!| | | | | | | | | | | | | | | | | | }}
+{{Family tree | | D05 | | | | D06 | | | | D07 | | | | D08 | | | | | | | | D09 | | | | D05=New LBB|D06=Old LBB|D07=LBB of unknown duration|D08=Complete LBB|D09=Incomplete LBB }}
+{{Family tree/end}}
 ==Related Chapters==
 *[[Electrical conduction system of the heart]]

v t e Electrocardiography
Overview	History of the EKG • EKG interpretation basics • Normal sinus rhythm
EKG Complexes	P wave • QRS complex • ST Segment • T wave • T wave alternans • Tombstone T wave • U wave Osborn wave • H wave • K wave • Delta wave NSSTW changes
EKG Intervals	PR Interval • QRS Interval • ST Interval • QT Interval
Conduction System & Bradycardia	Cardiac pacemaker • SA node • AV node• Bundle of His • Purkinje fibers • Sinus bradycardia • First Degree AV Block • Second Degree AV Block • Complete or Third-Degree AV Block • Concealed conduction • AV Junctional Rhythms • LBBB • LAHB • LPHB • RBBB • Trifascicular block
Atrial Arrhythmias	Sinus tachycardia • Premature Atrial Contractions (PACs) • Ectopic Atrial Rhythm • Paroxysmal Atrial Tachycardia (PAT) • Paroxysmal Atrial Tachycardia (PAT) with Block • Multifocal Atrial Tachycardia (MAT) • Atrial Flutter • Atrial Fibrillation • Wandering atrial pacemaker
Ventricular Arrhythmias	Differential Diagnosis of Tachycardia with a Wide QRS Complex • Accelerated Idioventricular Rhythm • Ventricular Parasystole • Premature Ventricular Contractions (PVCs) • Ventricular tachycardia • Ventricular Fibrillation • Sudden cardiac death
EKG Abnormalities in Disease States	Hypertrophy & Dilatation • Right atrial enlargement • Left atrial enlargement • Biatrial enlargement • Left Ventricular Hypertrophy • Right Ventricular Hypertrophy • Biventricular Hypertrophy • Acute myocardial infarction • NSTEMI • STEMI • Tombstone ST elevation • Right ventricular myocardial infarction • Atrial infarction Pre-excitation Syndromes • Wolff-Parkinson-White Syndrome • Lown Ganong Levine Syndrome • Mahaim Type Preexcitation Cardiomyopathies • Arrhythmogenic Right Ventricular Dysplasia • Dilated Cardiomyopathy • Hypertrophic Cardiomyopathy Drug Effects on the EKG • Adenosine • β-blockers • Digitalis • Quinidine • Procainamide • Disopyramide • Lidocaine • Tocainide and Mexiletine • Phenytoin • Encainide, Flecainide and Propafenone • Amiodarone • Bretylium • Ca Channel Blockers • Phenothiazines • Tricyclic Antidepressants • Lithium Congenital Heart Disease • Dextrocardia • Atrial Septal Defect • Ventricular Septal Defect • Tetralogy of Fallot • Conjoined Twins or Siamese Twins • Congenital heart block Electrolyte Disturbances • Hyperkalemia • Hypokalemia • Hypercalcemia • Hypocalcemia • Nonspecific Changes Other Heart Diseases • Pericarditis • Myocarditis • Tamponade • Heart Transplantation • Sick Sinus Syndrome • Long QT Syndrome Inherited Disease • Brugada Syndrome Systemic Diseases • CNS Disease • Cardiac Tumors Heart Transplantation • EKG Changes in patient with Heart Transplantation Exogenous Effects • Hypothermia • Chest Trauma • Insect Bites • Electric Injuries
Technical Issues and Potential Errors in Interpretation	Artifacts • Lead Placement Errors • The EKG in a Patient with a Pacemaker • EKG in athletes