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Left Bundle Branch Block

Left bundle branch block (LBBB) is seen on the ECG when there is failure of the electrical impulse to be conducted via the His-Purkinje fibers.


Patients who present with LBBB may have a congenital heart defect or prior cardiac surgery. The medical history should include symptoms like exercise tolerance, presence of fatigue, dyspnea, syncope, orthopnea and falls. The duration and intensity of symptoms should be recorded.

Physical exam may be unremarkable in some patients with LBBB, but auscultation may reveal a diminished or absent first heart sound and/or reversed splitting of the 2nd heart sound. Patients with heart failure may present with the following features:

  • Voltage-clamp measurements in a heterologous expression system of HEK293T cells showed that HCN4(G811E) slightly reduced whole-cell HCN4 channel conductance, whereas it did not affect the gating kinetics, unitary conductance, or cAMP-dependent modulation[ncbi.nlm.nih.gov]
  • Back Injury Back Training Balance Training Bands and Pulleys Baseball Basketball Behavior Bilateral Sacroilitis Biofeedback Biomechanics Biomotor Abilities Blood Pressure Bobsleigh Body Building Body Composition Body Fat Testing Bone Structure Boot Camp[ptonthenet.com]
  • Abstract We present a case of a 74-year-old woman, who was on nitrofurantoin treatment for urinary tract infection (UTI), with fever and chills 7 hours after taking nitrofurantoin. She was hospitalised and evaluated for worsening UTI and sepsis.[ncbi.nlm.nih.gov]
Exertional Dyspnea
  • Abstract A 61-year-old man was referred to our hospital with exertional dyspnea. Electrocardiography showed atrial fibrillation (AF) with a heart rate of 116 bpm and left bundle branch block (LBBB).[ncbi.nlm.nih.gov]
Recurrent Chest Pain
  • Over 80% of patients with CSFP experience recurrent chest pain. A relationship between CSFP and ventricular arrhythmias has also been reported.[ncbi.nlm.nih.gov]
Heart Disease
  • Before taking ranolazine, on the background of conventional treatment of coronary heart disease, the patient developed stable angina and persistent left bundle branch block, atrial fibrillation.[ncbi.nlm.nih.gov]
  • In children LBBB is usually associated with congenial heart disease and is quite rare in normal healthy children.[symptoma.com]
  • We present the case of a patient with ischemic heart disease and intermittent left bundle branch block, reproducibly induced by laughter.[ncbi.nlm.nih.gov]
  • CONCLUSIONS: An occupational physician should take into account that factors such as age and low cardiovascular risk do not always exclude heart disease, especially when there are conduction system abnormalities that can mask possible coronary artery[ncbi.nlm.nih.gov]
  • Most people with left bundle branch block have some form of underlying heart disease.[verywell.com]
Neck Pain
  • A 21-year-old woman with asthma and allergic rhinitis presented with neck pain and cough for 6 months with no other complaints. Physical exam was normal except for fever and minimal expiratory wheezes.[ncbi.nlm.nih.gov]


In a patient with LBBB, blood work is not essential as it is often noncontributory. However, in symptomatic patients it is important to order cardiac biomarkers to ensure that the patient has not suffered a myocardial infarction. Levels of creatine kinase, troponin and LDH should be serially ordered in symptomatic patients. If the cause of LBBB is due to an infection or an inflammatory process, ESR or CRP levels should be ordered. While not specific for myocarditis, they do help in assessing the effects of treatment. Other blood work will depend on the suspected cause of the LBBB.

Routine blood work that is done includes:

  • Complete blood count
  • Electrolyte levels
  • Renal and liver function
  • Coagulation profile
  • Blood cultures if endocarditis is suspected
  • Lipid profile

Additional studies

  • Serial ECGs are required in patients with LBBB. There are criteria that have been established to determine the presence of a LBBB on the ECG. If amyocardial infarction is suspected in the presence of LBBB, one needs to use Sgarbossa’s scoring criteria [7].
  • A chest X-ray is done to determine presence of heart failure.
  • Some patients in whom the diagnosis is not clear may require 24 hour holter monitoring to determine presence of any other co-existing arrhythmia [8].
  • An echocardiogram is usually done to assess heart and valve function. The method can also detect presence of vegetations on the leaflet.
Left Axis Deviation
  • Left bundle branch block is usually associated with normal or left axis deviation. Rarely the ECG shows a left bundle branch block with changing QRS morphology and changing axis deviation.[ncbi.nlm.nih.gov]
  • An electrocardiogram revealed left axis deviation (LAD) in 1988 and slightly prolonged PQ intervals in 1993. Complete left bundle branch block (CLBBB) with LAD developed in May 1995.[ncbi.nlm.nih.gov]
  • Left bundle branch block is usually associated with normal or left axis deviation. Rarely the ECG shows a LBBB with changing QRS morphology and changing axis deviation.[ncbi.nlm.nih.gov]
  • Abstract An electrocardiogram (ECG) of an 82-year-old woman (see Figure 1 ) showed complete left bundle branch block (LBBB: QRS duration 148ms), left axis deviation to -52o, rS complexes in V1–V6, absence of septal Q-waves, and first-degree atrioventricular[radcliffecardiology.com]
  • Left axis deviation in addition to left bundle branch block did not imply more frequent coronary atherosclerosis. Footnotes[circ.ahajournals.org]
Wide QRS Complex
  • However, in some patients, LBBB may vary with heart rate, and during episodes of AF in LBBB, aberrant ventricular conduction, or wide QRS complex tachycardia (Ashman beats) can occur.[ncbi.nlm.nih.gov]
  • A 12-lead ECG in the ER showed sinus tachycardia at 118 beats/min, wide QRS complexes, peaked T waves and left bundle branch block-like pattern. The initial basic metabolic panel revealed a serum potassium level of 8.8 mEq/L.[cardiologyres.org]
  • Left bundle branch block ECG characteristics of a typical LBBB showing wide QRS complexes with abnormal morphology in leads V1 and V6.[en.wikipedia.org]
  • With left bundle branch block, the wide QRS complex appears upright in certain leads, and downward in others.[verywell.com]
  • Henneman et al. [ 32 ] studied 75 patients with heart failure, depressed left ventricular function, and wide QRS complex using gated SPECT and two-dimensional echocardiography, including tissue Doppler imaging (TDI).[link.springer.com]
Absent A-Waves
  • The presence of a mid-QRS notching in more than two consecutive leads was a good predictor for the presence of SF (P 0.01), and when combined with an absent R-wave in lead V1, the presence of SF is very likely (P 0.001).[ncbi.nlm.nih.gov]
  • Electrocardiographically, a LBBB is defined as QRS duration greater than or equal to 120 ms; a broad-notched or slurred R wave in leads I, aVL, V5, and V6; absent Q waves in leads I, V5, and V6 ; and an R peak time 60 ms in leads V5 and V6 but normal[emdocs.net]


All patients who have been diagnosed with LBBB need a thorough workup of their heart. It is important to treat the underlying cause if found. There is no medical therapy to treat LBBB. In all asymptomatic patients the treatment is an annual ECG.

For patients who have syncope or symptoms of heart failure, a dual chamber cardiac pacemaker is required. While resynchronization therapy may help improve symptoms, survival is not always improved. The improvement in patients is variable and not predictable [9]. Pacemakers can be inserted by the cardiologist or cardiac surgeon under local anesthesia. In most cases, progression to a complete heart block is rare.


Left bundle branch block does not progress to a complete heart block in most cases. The overall prognosis of LBBB depends on coexisting cardiac disease. In patients with heart failure, biventricular pacing can improve symptoms and morbidity. In general, the higher the cardiac morbidity, the poorer is the prognosis in the presence of LBBB. Patients who develop LBB after open heart surgery procedures generally do not have a higher morbidity as long as the primary disorder has been surgically corrected.


LBBB has several causes which include the following:

  • Congenital abnormalities of the conduction system (eg. Lev’s disease or Lenegre-lev syndrome where there is heart block due to calcification and fibrosis of the electrical pathways).
  • Certain congenital disorders like Noonan syndrome and Down syndrome are also associated with heart defects like endocardial cushion defects, complete AV canal or large ventricular septal defects. Infants with tricuspid atresia, single ventricle, or double outlet ventricle are also at high risk for developing LBBB.
  • Congenital anatomical malformations that primarily those that involve the left ventricular outflow tract (eg. subvalvar resection of subvalvar aortic tissue) and surgical repair of VSD.
  • Post open heart surgery procedures such as surgery on the septum, left ventricular outflow tract, myomectomy, aortic valve replacement or procedures to enlarge the aortic annulus.
  • Percutaneous technique of septal ablation with alcohol for treatment of idiopathic hypertrophic cardiomyopathy.
  • Percutaneous catheter closure of muscular septal defect.
  • May also be seen in patients with left ventricular hypertrophy, viral or bacterial (eg. diphtheria) myocarditis, cardiomyopathy and following myocardial infarction [3] [4].
  • Endocarditis of the aortic valve and rheumatic fever that involves the aortic valve [5] [6].
  • Prenatal exposure to HIV can sometimes present with LBBB.
  • Wolff-Parkinson-White syndrome
  • Left ventricular hypertrophy from prolonged hypertension.


In children LBBB is usually associated with congenial heart disease and is quite rare in normal healthy children. In adults, LBBB may appear after a variety of open heart surgery procedures on the left ventricular outflow tract such as after aortic valve replacement, surgery on the septum, or aortic annulus. The exact number of people with LBBB is not known but the numbers are not miniscule. Because many patients remain asymptomatic, they never come to medical attention. The disorder can occur in people of all ages and in all races.

Sex distribution
Age distribution


Left bundle branch block develops when there is interruption of the electrical impulse in the heart. The conduction from the sinus node is normal until it reaches the bundle of His-Purkinje tissues. At this point the electrical conduction may be delayed or absent. There can be either a complete LBBB or an incomplete left bundle branch block known as a hemiblock. The damage to the electrical conduction may be a result of structural defects in the heart since birth (eg. endocardial cushion defects) or they may be caused during open heart surgery on the left ventricular outflow tract.


Prevention of LBBB is not possible in most cases. For children born with heart defects, it is important to follow up closely with a cardiologist to ensure that the disease is not progressing. If the child becomes symptomatic, pacing may be required. Adults who undergo open heart surgery and develop LBBB generally do not show symptoms as long as surgery corrected the primary disorder. However, symptomatic adults who develop heart failure may need a permanent pacemaker. For patients who developed an LBBB after a myocardial infarction, change in lifestyle is important. This means eating healthy, discontinuing smoking, regular exercise and remaining compliant with medications. Levels of cholesterol and blood sugar should be controlled to prevent progression of atherosclerotic heart disease.


Left bundle branch block (LBBB) is a conduction abnormality seen on the ECG when the regular sequence of electrical impulse is altered in the His-Purkinje fibers. In the majority of cases, this conduction abnormality is seen in people with some type of underling heart disease. However, it must be noted that LBBB may also be seen in people with no symptoms and in the presence of any structural defect in the heart. When LBBB is identified on the ECG it often makes the diagnosis of a myocardial infarction difficult. In addition, this conduction abnormality also interferes with the ECG analysis in patients who undergo exercise testing. Patients who have a low ejection fraction and develop LBBB, generally tend to develop dyssynchronous ventricular beats that eventually results in congestive heart failure. It is important to realize that LBBB may not always cause symptoms but it is not a benign disorder [1] [2].

Patient Information

There are many causes of left bundle branch block (LBBB) that include heart disease that developed at birth, open heart surgery procedures and following a heart attack. Patients should be told that LBBB rarely progresses to a complete heart block or cause sudden death and to watch out for other symptoms of heart disease like shortness of breath, swelling of the legs, chest pain or fatigue. They should be encouraged to have annual visits for a physical checkup and undergo a 12 lead ECG if they develop chest pain or dizziness. All symptomatic patients should be told to have more frequent visits with their cardiologist. Patients should be told that there may be a need for a pacemaker if the symptoms of heart failure do not respond to medications. Patients with LBBB need instructions on what types of activities they can carry out. Patients who are symptomatic or have a tendency to develop arrhythmias need to limit themselves from intense physical activity. Those patients without symptoms can perform most daily living activities.



  1. Koskinas KC, Ziakas A. Left Bundle Branch Block in Cardiovascular Disease: Clinical Significance and Remaining Controversies. Angiology. 2015 Jan 13
  2. Erdogan O, Kepez A, Atas H. Left bundle branch block type wide QRS tachycardia: what is the most likely diagnosis derived from the ECG? Heart. 2015 Mar 1;101(5):390.
  3. Farré N, Mercè J, Camprubí M, Mohandes M, Guarinos J, Fernández F, Oliva X, Bardají A; on behalf of the CODI IAM Registry Investigators. Prevalence and outcome of patients with left bundle branch block and suspected acute myocardial infarction. Int J Cardiol. 2014 Dec 30;182C:164-165.
  4. Anghel L, Arsenescu Georgescu C Particularities of coronary artery disease in hypertensive patients with left bundle branch block. Maedica (Buchar). 2014 Dec;9(4):333-7.
  5. Sundh F, Simlund J, Harrison JK, Hughes GC, Vavalle J, Maynard C, Strauss DG, Wagner GS, Ugander M. Incidence of strict versus nonstrict left bundle branch block after transcatheter aortic valve replacement. Am Heart J. 2015 Mar;169(3):438-44
  6. Elterman KG, Mallampati SR, Tedrow UB, Urman RD. Postoperative episodic left bundle branch block. A A Case Rep. 2014 Feb 15;2(4):44-7.
  7. Smith SW, Dodd KW, Henry TD, Dvorak DM, Pearce LA. Diagnosis of ST-elevation myocardial infarction in the presence of left bundle branch block with the ST-elevation to S-wave ratio in a modified Sgarbossa rule. Ann Emerg Med. 2012 Dec;60(6):766-76
  8. Mordi I, Tzemos N. Non-invasive assessment of coronary artery disease in patients with left bundle branch block. Int J Cardiol. 2015 Jan 29;184C:47-55
  9. Eschalier R, Ploux S, Ritter P, Haïssaguerre M, Ellenbogen KA, Bordachar P. Nonspecific intraventricular conduction delay: Definitions, prognosis, and implications for cardiac resynchronization therapy. Heart Rhythm. 2015 Jan 19. pii: S1547-5271(15)00073-9.

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Last updated: 2018-06-21 23:03