View source for Left bundle branch block

{{Infobox_Disease |
  Name           = {{PAGENAME}} |
  Image          = Left bundle branch block ECG characteristics.png|
  Caption        = ECG characteristics of a typical [[LBBB]] showing wide [[QRS]] complexes with abnormal morphology in leads V1 and V6 |
  DiseasesDB     = 7352 |
  ICD10          = {{ICD10|I|44|7|i|30}} |
  ICD9           = |
  ICDO           = |
  OMIM           = |
  MedlinePlus    = |
  eMedicineSubj  = ped |
  eMedicineTopic = 2501 |
  MeshID         = |
}}
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{{WikiDoc Cardiology Network Infobox}}
{{WikiDoc Cardiology News}}
{{CMG}}
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'''Associate Editors-In-Chief:''' {{CZ}}; Atif Mohammad, MD
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'''Synonyms and related keywords:''' LBBB

'''Left bundle branch block ([[LBBB]])''' is a cardiac conduction abnormality seen on the [[electrocardiogram]] ([[ECG]]). In this condition, activation of the [[left ventricle]] is delayed, which results in the left ventricle contracting later than the [[right ventricle]].

==[[EKG]] diagnosis==

The criteria to diagnose a [[left bundle branch block]] on the [[electrocardiogram]]:

* The heart rhythm must be supraventricular in origin
* The [[QRS]] duration must be = or > 120 ms
* There should be a QS or rS complex in lead V1
* There should be a monophasic R wave in leads I and 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]].
==Causes of [[LBBB]]==
Among the causes of [[LBBB]] are:
* [[Hypertension]]
* Acute [[myocardial infarction]]
* Extensive cases of [[coronary heart disease|coronary artery disease]]
* Primary disease of the cardiac electrical conduction system
== Reading Ischemia In The Presence Of [[LBBB]] ==

[[LBBB]] can simulate an [[MI]] due to the associated secondary ST changes and pseudoinfarct q waves that it causes, and furthermore it can mask the [[EKG]] changes of an [[MI]].

===Sgarbossa Criteria===

An EKG scoring system was developed and the independent criterion were assessed on patients from the GUSTO-1 trial patients were scored from 0-5 for presence of LBBB in the context of acute myocardial infarction.<ref>{{cite journal |author=Sgarbossa EB, Pinski SL, Barbagelata A, Underwood DA, Gates KB, Topol EJ, Califf RM, Wagner GS |title=Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators |journal=[[N. Engl. J. Med.]] |volume=334 |issue=8 |pages=481–7 |year=1996 |month=February |pmid=8559200 |doi= |url=http://content.nejm.org/cgi/pmidlookup?view=short&pmid=8559200&promo=ONFLNS19}}</ref>

<table width="80%" height="100px">
 <tr>
<td>Criteria </td>                                                       
  <td>Score</td>
</tr> 
<tr>
<td> 1.ST-segment elevation ≥ 1 mm and concordant with QRS complex </td> 
   <td>     5  </td>    
</tr> 
<tr>  
<td> 2.ST-segment depression ≥ 1 mm in lead V1,V2 or V3 </td>
   <td>     3  </td>                
</tr>
<tr>
<td> 3.ST-segment elevation ≥ 5 mm and discordant with QRS complex </td>
   <td>     2  </td>     
</tr> 
</table>  



== Pseudoinfarct Patterns: Simulation of an [[acute MI|Anterior MI]] ==
# Can cause poor R wave progression. Often see a decrease in the amplitude of R waves to the midprecordium in the absence of a septal infarct.
# QS complexes are often seen in the right precordial leads in uncomplicated [[LBBB]] and they may even extend as far out as V5 or V6.
# Non infarctional Q waves may be seen in aVL.
# The Reason: [[LBBB]] causes a loss of the normal septal r waves in the right precordial leads. The septum is no longer being depolarized from left to right as it normally does because of the delay down the left bundle.
# There can occasionally be Rs complexes in V1. These unanticipated initial positive forces are due to early RV depolarization and may actually mask the q waves (i.e. loss of initial septal forces) that accompany an [[acute MI|anteroseptal MI]].

== Simulation of an Inferior [[MI]] ==
# Noninfarctional QS complexes can be seen in leads II, III, and aVF in [[LBBB]].
# There are a number of autopsy cases were there are QS waves inferiorly without evidence of an [[MI]].
# There are several reported cases of intermittent [[LBBB]] in which the QS waves inferiorly were present only in the aberrantly conducted beats.
# Conversely, [[LBBB]] may mask the development of Q waves in an [[MI]].

== Secondary [[ST segment]] and [[T Wave]] Changes ==
# Primary [[ST segment]] and [[T wave]] changes are repolarization changes that are seen with ischemia or electrolyte imbalance and reflect actual changes in the myocardial action potentials.
# Secondary [[ST segment]] and [[T wave]] wave changes occur when the sequence of ventricular activation is altered without any disturbance in the electrical properties of the myocardial cells such as is seen in [[LBBB]].
# As a result of secondary [[ST segment]] and [[T wave]] wave changes, the [[QRS]] and the [[T wave]] vectors are oriented in opposite directions which is known as discordance of the [[QRS]] and [[T wave]] vectors.
# Thus, the [[QRS]] is often predominantly negative in the right precordial leads while the [[T wave]] is oriented positively. In those leads where there is a tall positive R wave there is a negative [[T wave]].
# These secondary [[ST segment]] and [[T wave]] changes often mimic infarction, and furthermore they may mask the [[ST segment]] and [[T wave]] changes of an MI.
# Sometimes primary [[ST segment]] and [[T wave]] changes will be superimposed on the [[LBBB]] pattern and the following suggests the diagnosis of ischemia or infarction:
#* [[ST segment]] elevation in leads with a predominant R wave. In uncomplicated [[LBBB]], the [[ST segment]] is isoelectric or depressed.
#* T wave inversions in the right to midprecordial leads or in other leads with a predominantly negative [[QRS]]. In other words there is an absence of discordance, and there is the presence of concordance.
#* Morphology: In leads with a predominant R wave, the [[ST segment]] begins to slope downwards and blends into the [[T wave]]. The ascending limb of the [[T wave]] ascends back to the baseline at a more acute angle.           		
#* The ischemic [[T waves]] have a more symmetric appearance and a slightly upwardly bowed [[ST segment]].
#* [[ST segment]] and [[T wave]] elevations simulating acute infarction: The [[ST segment]] can be markedly elevated (up to 10 mm or more at the J point ) in leads with a QS or rS segment in uncomplicated [[LBBB]]. In addition, there can be a loss of R wave progression.
#* T wave inversions in intermittent [[LBBB]]: May develop deep [[T wave]] inversions in the right to midprecordial leads of normally conducted beats in the absence of CAD. These [[T wave]] inversions are deepest in leads V1 to V4 with a symmetric or coved appearance.

== Etiology of Q Waves ==
# As described earlier, in [[LBBB]] there is a loss of depolarization from left to right, which produced an initial r wave in the right precordial leads. 
# Now there is depolarization from right to left. Consequently the initial r wave is lost, and the non infarctional QS complexes may appear in the precordial leads.
# The reversal of septal activation results in RS complexes in the left precordial leads.

== Can You Read a Left Ventricular Free Wall Infarction In the Presence of a [[LBBB]]? ==
# No. This pattern of infarction results in abnormal q waves in the midprecordial to lateral precordial leads.
# In [[LBBB]] the initial septal depolarization forces are directed from right to left. These leftward septal forces will produce an initial R wave in the midprecordial to the lateral precordial leads, masking the loss of potential q waves produced by the infarction. 
# Therefore left ventricular free wall infarction by itself will not produce diagnostic q waves in the presence of a [[LBBB]].
# Poor R wave progression is seen in uncomplicated [[LBBB]].

== Can You Read a Septal Infarction in the Presence of [[LBBB]]? ==
# Yes. Again the septal forces are directed to the left in [[LBBB]].
# If enough of the septum is infarcted to eliminate these initial leftward septal forces, abnormal QR, [[QRS]], or qrs types of complexes may appear in the midprecordial to lateral precordial leads.
# These initial q waves may reflect posterior and superior forces from the spared basal portion of the septum.
# Small q waves of 0.03 sec or less may be seen in leads I, V5 to V6 in uncomplicated [[LBBB]].
# The presence of q waves laterally is an example of false localization. <ref>Myocardial Infarction, Electrocardiographic Differential Dx, Ary L. Goldberger, 3rd ed., Mosby Co., St. Louis, 1984, p.85   93.
</ref>

==Treatment ==
* Medical Care: Patients with LBBB require complete cardiac evaluation, and those with LBBB and         near-syncope or syncope may require a pacemaker.
* Surgical Care: Some patients with LBBB, a markedly prolonged QRS, and congestive heart failure may benefit from a pacemaker, which provides rapid left ventricular contractions.

==Classification==
Some sources distinguish between a "left anterior fascicular block" (LAFB)<ref>{{GPnotebook|x20050921122910832459}}</ref> and a "left posterior fascicular block" (LAPB).<ref>{{GPnotebook|x20050921123129832459}}</ref> This refers to the bifurcation of the left [[bundle branch]].

==EKG Examples==

<div align="center">
<gallery heights="175" widths="175">
Image:12leadLBTB.png|Left Bundle Branch Block
Image:12leadLBTB002.jpg|Left Bundle Branch Block
</gallery>
</div>


<div align="center">
<gallery heights="175" widths="175">
Image:c10.ht10.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
Image:c11.ht11.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
</gallery>
</div>


<div align="center">
<gallery heights="175" widths="175">
Image:c4.htm4.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
Image:c5.htm5.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
</gallery>
</div>


<div align="center">
<gallery heights="175" widths="175">
Image:c6.htm6.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
Image:c7.htm7.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
</gallery>
</div>


<div align="center">
<gallery heights="175" widths="175">
Image:c8.htm8.jpg|Left Bundle Branch Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
Image:c9.htm9.jpg|Left Bundle Branch Block + Left Anterior Fascicular Block <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
</gallery>
</div>


<div align="center">
<gallery heights="175" widths="175">
Image:ECG RBTB LAtrD.jpg|Left Bundle Branch Block + Left Anterior Fascicular Block + Left atrial enlargement
Image:r10.ht35.jpg|Left Bundle Branch Block + Supraventricular tachycardia <small> [http://www.ganseman.com/ecgbibnl.htm#_top000 Image courtesy of Dr Jose Ganseman]</small>
</gallery>
</div>


<div align="center">
<gallery heights="175" widths="175">
Image:LBBB with Lateral Q waves.CMG.jpg|LBBB with Lateral Q waves <small>Image courtesy of [[C. Michael Gibson]] MS MD and Copylefted</small>
Image:LBBB.CMG.jpg|Left Bundle Branch Block <small>Image courtesy of [[C. Michael Gibson]] MS MD and Copylefted</small>
</gallery>
</div>

==See also==
* [[Bundle branch block]]
* [[Right bundle branch block]]

== References ==
{{Reflist}}

==External links==
* http://library.med.utah.edu/kw/ecg/mml/ecg_lbbb.html

==Additional resources==
* [http://en.ecgpedia.org ECGpedia: Course for interpretation of ECG]
* [http://www.anaesthetist.com/icu/organs/heart/ecg/ The whole ECG - A basic ECG primer]
* [http://www.ecglibrary.com 12-lead ECG library]
* [http://www.ecgsim.org Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG]
* [http://heartcenter.seattlechildrens.org/what_to_expect/electrocardiogram.asp ECG information from Children's Hospital Heart Center, Seattle]
* [http://www.regionalpci-stemi.org/id10.html ECG Challenge from the ACC D2B Initiative]
* [http://0-www.nhlbi.nih.gov.innopac.up.ac.za:80/health/dci/Diseases/ekg/ekg_what.html National Heart, Lung, and Blood Institute, Diseases and Conditions Index]
* [http://www.ecglibrary.com/ecghist.html A history of electrocardiography]
* [http://www.health.gov.mt/impaedcard/issue/issue1/ipc00103.htm EKG Interpretations in infants and children]


{{Electrocardiography}}
{{SIB}}

[[Category:Cardiology]]
[[Category:Electrophysiology]]
[[Category:Emergency medicine]]

[[de:Linksschenkelblock]]
[[pt:Bloqueio do ramo esquerdo do feixe de His]]
[[fr:Bloc de branche]]
[[tr:Sol dal bloğu]]

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