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Left Bundle Branch Block

Left bundle branch block refers to a conduction block in any part of the left-sided conduction
 pathway from the bundle of His to the fascicles which slows the depolarization and contraction
 of the left ventricle ( Assessment of an incidental finding of the left bundle branch 
block David Warriner et al April 2005 )
Activation of the left ventricle is delayed with respect to the interventricular septum – leading to an inefficient pumping action In the normal direction of of septal depolarization is reversed from left to right to right to left LBBB completely modifies the the electrical activation of the left ventricle and the QRS complex on ECG The consequence is impairment of systolic and diastolic left ventricular function
How commonFirst described more than 100 yrs ago LBBB is a rare finding in young people and almost never happens before age 35 Estimated prevalence is between 0.1 % to 0.8 % Approximately 33 % of patients with heart failure have LBBB It increases with age – from < 1 % before age 50 to 6 % by 80 yrs Incidental LBBB occurs in up to 1.5 % of healthy people without symptoms or signs of CV disease Patients who have no CV risk factors and develop LBBB at a younger age have better prognosis than those who developed LBBB during or after the 5th decade Individuals with LBBB represent approximately 2 % of all patients who seek treatment with suspected ACS
CausesLittle known about aetiology of LBBB Often associated with structural heart disease particularly dilated cardiomyopathy Factors closely associated with LBBB development include
○ arterial hypertension
○ coronary artery disease
○ valvular heart disease
○ cardiomyopathies
○ myocarditis
○ other abnormalities as LVH and ST-T changes Other implicated theories
○ cardiac stretching
○ cardiac scarring or infiltration
○ ischaemia , infarction
○ fibrosis of the conduction system Often seen as a complication of Transcatheter aortic valve replacement ( TAVR )
TAVR induced LBBB rates vary from 7 5 to 83 % Hyperkalaemia ( rarely ) Digoxin toxicity Severe trauma ( for e.g car accident ) Following AMI , myocarditis
Why important ? Integrative marker of overall cardiac risk Patient likely to suffer major cardiac adverse events as
○ acute myocardial infarction ( AMI )
○ sudden cardiac death
○ coronary artery disease
○ heart failure
○ stroke
○ revascularization It is not clear if its the LBBB itself or its combination with other CV disorders 
that adversely affects mortality In Framingham study half of CV deaths occurred in subjects with LBBB
Presentationusually an incidental finding in an asymptomatic patient look for previous evidence of LBBB
○ search the system for previous documentation
○ look for old ECGs
○ look at hospital letters
○ ask the patient if he / she is aware of the diagnosis review the ECG – look at the differentials find reason why the ECG was done review the patient face to face / tel if situation not clear
Diagnostic criteriaLBBB diagnostic criteria are not straightforward
 or standardized yet. Stricter criteria have evolved lately.

AHA / ACC criteria for a complete LBBB are Rhythm must be super-ventricular origin QRS duration of > 120 ms Lead V1 should have either a QS or a small r wave with large S wave Lead V6 should have a notched R wave and no Q wave
Recent studies utilizing endocardial mapping have demonstrated that > 30 % of the patients meeting the conventional ECG criteria of LBBB did not have significant delays between the start of activation of the right and LV endocardium and therefore actually do not have complete LBBB
New finding and patient unwellUndertake a clinical assessment Is this an MI ? r/o ACS ( acute coronary syndrome ) features
always consider the diagnosis -new onset LBBB with concerning clinical symptoms could indicate a pathology particularly MI ? heart failure Review patient history Managing patients with LBBB and MI is challenging Patient reports LOC/ Syncope
New finding and patient asymptomatic Ask about any previous episodes of chest tightness , breathlessness or syncope Enquire family h/o IHD / sudden death patients with identification of an asymptomatic cause for e.g aortic stenosis Asymptomatic consequence of LBBB for e.g left ventricular dysfunction Asymptomatic bradycardia Alternating right and left BBB Patients with pauses longer than 3 seconds on Holter monitoring
Differentials- interventricular conduction delay paced rhythm incomplete LBBB a ventricular rhythm ( run of PVCs ) without superventricular stimulation can appear very similar to a LBBB
Tests / managementIn primary care arrange for FBC ,, Us & Es , LFT , Lipid profile , serum glucose and CRP Echocardiography Holter monitor – if patient reports dizziness and syncope Nuclear imaging – SPECT to characterize LV perfusion and metabolism mismatch Cardiac MRI to assess LV mechanical dyssynchrony and predict response to CRT Cardiac synchronization therapy has dramatically changed the management of HF patients with LBBB
Sgarbossa criteriaIt has been traditionally thought/ taught that MI cannot be diagnosed if LBBB is present due to characteristic ECG changes caused by altered ventricular depolarization. In 1996 Sgarbossa et al published findings from GUSTO-1 trial to help identify criteria for diagnosis of acute myocardial infarction ( AMI ) in presence of LBBB The Sgarbossa criteria consist of 
○ ST segment elevation of 1 mm or more in concordant with the QRS complex ( i.e positive complex ) in any lead ( score of 5 )
○ ST-segment depression of 1 mm or more in lead V1 , V2 or V3
( score of 3 ) and
○ ST segment elevation of 5 mm or more discordant with the QRS complex in any lead ( score of 2 ) When combined these 3 ECG criteria yielded a sensitivity and specificity of approximately 78 % and 90 % respectively Sgarbossa criteria can be accessed via MD Calc- see under links and Modified Sgarbossa criteria were validated in 2015
Patients in the USA with LBBB are not allowed to pilot an aircraft or other heavy equipment In the UK car or motorcycle license holders do not need to 
inform DVLA but Bus , coach or lorry drivers need to inform the condition 
via VOCH1 form ( see links )


Patient information from Cedar Sinai which a non-profit hospital in Los Angeles- concise and a good read even for most people engaged in primary care
Mayoclinic on LBBB
Heartforlife co uk on LBBB
A page from Texas Heart Institute on LBBB
MHealth on LBBB
Cardiac resynchronisation therapy
Oxford University Hospital Implantation of a Cardiac Resynchronisation Therapy-Defibrillator
A useful explanatory video on You Tube
Some links to recognise ECG changes/criteria
Life in the Fastlane
Acadoole video- brilliant
Medicoapps video on BBB
EKG Guy 26 minutes video on LBBB
Teaching medicine on LBBB
ECG ( needs subscription )
European Society of Cardiology -2015 ESC Guidelines for the management
of patients with ventricular arrhythmias
and the prevention of sudden cardiac death
American College of Cardiology -LBBB in Patients With Suspected MI: An Evolving Paradigm Feb 28, 2017   |  Bryan Wilner, MDJames A. de Lemos, MD, FACC Ian J. Neeland, MD Expert Analysis
Left Bundle-Branch Block—Pathophysiology, Prognosis, and Clinical Management PIETRO FRANCIA, M.D., CRISTINA BALLA, M.D., FRANCESCO PANENI, M.D., MASSIMO VOLPE, M.D. Chair and Division of Cardiology, II Faculty of Medicine, Sant’Andrea Hospital, University “La Sapienza,” Rome, Italy

  1. Assessment of an incidental finding of left bundle–branch block April British journal of hospital medicine (London, England: 2005)76(4):196-9 DOI:10.12968/hmed.2015.76.4.196
  2. Evolving Considerations in the Management of Patients With Left Bundle Branch Block and Suspected Myocardial Infarction Ian J. NeelandMD,Michael C. KontosMDandJames A. de LemosMD JACC (Journal of the American College of Cardiology), 2012-07-10, Volume 60, Issue 2, Pages 96-105, Copyright © 2012 American College of Cardiology
  3. Foundation Francia, Pietro, Cristina Balla, Francesco Paneni, and Massimo Volpe. “Left Bundle‐branch Block—pathophysiology, Prognosis, and Clinical Management.”Clinical Cardiology30.3 (2007): 110-15.
  4. Web Das D, McGrath BM. Sgarbossa criteria for acute myocardial infarction.CMAJ. 2016;188(15):E395. doi:10.1503/cmaj.150195
  5. Elena Surkova, Luigi P. Badano, Roberto Bellu, Patrizia Aruta, Federica Sambugaro, Gabriella Romeo, Federico Migliore, Denisa Muraru, Left bundle branch block: from cardiac mechanics to clinical and diagnostic challenges,EP Europace, Volume 19, Issue 8, August 2017, Pages 1251–1271,
  6. Scherbak D, Hicks GJ. Left Bundle Branch Block (LBBB) [Updated 2019 Apr 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.Available from:
  7. Implications of Left Bundle Branch Block in Patient Treatment 
Author:Vineet Kumar,Rajesh Venkataraman,Wael Aljaroudi,Jose Osorio,Jaekyeong Heo,Ami E. Iskandrian,Fadi G. Hage Publication:The American Journal of Cardiology Publisher:Elsevier Date:15 January 2013
  8. Balla, Cristina, and Riccardo Cappato. “When to choose cardiac resynchronization therapy in chronic heart failure: type and duration of the conduction delay.” European heart journal supplements : journal of the European Society of Cardiology vol. 21,Suppl B (2019): B31-B35. doi:10.1093/eurheartj/suz026


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