Left Bundle Branch Block (LBBB)

Article Author:
Dmitriy Scherbak
Article Editor:
Gregory Hicks
Updated:
4/7/2019 12:26:49 AM
PubMed Link:
Left Bundle Branch Block (LBBB)

Introduction

Left bundle branch block (LBBB) is a common electrocardiographic (ECG) abnormality seen in patients whose normal cardiac conduction down both anterior and posterior left fascicles of the His-Purkinje system is compromised. Although LBBB is often associated with significant heart disease and is often the result of myocardial injury, strain or hypertrophy, it can also be seen in patients without any particular clinical disease. In isolation the presence of LBBB does not lend itself to any specific clinical concern, nor does it affect prognosis. However, in the proper clinical context, LBBB can of great consequence and importance, especially in patients presenting with acute chest pain, syncope and in those suffering from heart failure with reduced ejection fraction (HFrEF).[1] New onset LBBB in the proper setting of concerning clinical symptoms should always be considered a sign of pathology and can indicate myocardial infarction. New LBBB is considered an ST-segment elevation equivalent in patients presenting with chest pain.[2] Although the QRS and ST segments of an ECG are traditionally regarded as uninterpretable in the presence of LBBB, emerging Sgarbossa criteria have been developed allowing some interpretation of ECGs despite LBBB. [3][4]

Etiology

Stretching of cardiac tissue can lead to conduction issues between cardiac myositis. In this, the left bundle is no exception. The chief cause of LBBB is dilated cardiomyopathy. Specifically, enlargement of the left ventricle causing stretching and separation of the Purkinje fibers. The cause of dilated cardiomyopathy itself is quite varied including ischemic, infective, valvular, infiltrative, and inflammatory causes. Ischemic is, however, the most common cause. [1]

Epidemiology

LBBB is prevalent in about 0.06% to 0.1% of the general population. Approximately 33% of patients with heart failure have LBBB. Incidence increases with severity of left ventricular failure in heart failure patients. [1]

Pathophysiology

In addition to cardiac stretching, cardiac scarring or infiltration can disrupt the conduction system either through myocardial infarction or fibrosis like lenegre's disease or amyloidosis. [1]

History and Physical

LBBB itself is asymptomatic, there are no signs or symptoms other than the distinct pattern on EKG. [1][5]

Evaluation

LBBB is often detected on ECG. Diagnostic criteria are defined by the American College of Cardiology (ACC) and American Heart Association (AHA) as follows:

  1. Rhythm must be of super-ventricular origin (EG: ventricular activation coming from atrial or AV nodal activation)
  2. QRS Duration greater than 120 ms
  3. Lead V1 should have either a QS or a small r wave with large S wave
  4. Lead V6 should have a notched R wave and no Q wave [6]

Treatment / Management

LBBB itself has no specific treatment. The condition is usually permanent and requires treatment of underlying disorders.[1] The exception to this is in HFrEF with sinus rhythm, and LBBB with QRS duration greater than 150 ms with NYHA class II-IV heart failure will benefit from cardiac resynchronization therapy as recommended by the ACC and AHA. In addition to proper medical therapy, CRT has been shown to reduce death in this population by up to 37%. Cardiac re-synchronization should also be considered in patients either without sinus rhythm (EG atrial fibrillation) and QRS duration of 120 to 149 but is a weaker recommendation. It should be noted that CRT does not remove the LBBB but is accomplished using a bi-ventricular pacemaker to pace both left and right ventricle simultaneously. This process circumvents the ventricle's conduction system entirely. [7]

Differential Diagnosis

Differentials for LBBB include intra-ventricular conduction delay - which can result in similar ECG findings but often will not have an R wave in V6. A paced rhythm can often be confused with LBBB but again often does not have an R wave in V6 and pacer spikes are usually seen. An LBBB pattern with QRS duration less than 120 ms is called an incomplete LBBB. A ventricular rhythm (run of PVCs) without super-ventricular stimulation can appear very similar to a left bundle branch block and in certain uncommon situations would be indistinguishable from LBBB. [6]

Prognosis

In otherwise healthy individuals, LBBB does not confer any specific or additional risk.  Mortality hazard ratio (HR) for LBBB is only 1.3 of normal. However, in patients with new onset, LBBB mortality HR is greater than 10-times normal.[1] Specific at-risk populations of patients with LBBB are those who are presenting with chest pain and have new-onset LBBB which should be considered equivalent to ST-segment elevation.[2] In patients with heart failure, the presence of left bundle branch block is associated with increased cardiovascular outcomes and mortality. However, in a recent study which attempted to isolate LBBB's sole contribution to outcomes found that if contributions of confounders are excluded LBBB contributes far more modestly to poor outcomes. This is likely because LBBB is more of a symptom of dilated cardiomyopathy as opposed to a causative agent in the progression of the disease.[7]

Patients with LBBB are restricted from piloting aircraft in both the United States and the United Kingdom. This is due to LBBB being a possible pre-cursor to complete atrioventricular block. Such association is supported by epidemiologic data and patients presenting with syncope or pre-syncope in the setting of LBBB should undergo testing with ECG and Holter monitor. [8]

Pearls and Other Issues

An ECG is often considered "uninterpretable" in the presence of LBBB. This is in fact false. There are many things that we can interpret on an ECG despite LBBB.

Clinicians can determine rate and rhythm. The LBBB only affects the left ventricle making any part of the QRS and ST segment uninterpretable, but the atrial rhythm is still valid.

In the setting of acute myocardial infarction, there are a set of criteria called Sgarbossa criteria which can be applied to the ECG to increase predictive value for or against myocardial infarction. These criteria are not as good as ST-segment elevation in the absence of LBBB. Their sensitivity is only 49%, but specificity is greater than 90%.

  1. Concordant ST elevation greater than 1 mm in leads with a positive QRS complex (5 points)
  2. Concordant ST depression greater than 1 mm in V1 to V3 (3 points)
  3. Discordant ST elevation greater than 5 mm in leads in a negative QRS complex (2 points)

Three or more points means acute myocardial infarction.

Modified Sgarbossa criteria were validated in 2015. The sensitivity of the modified criteria increases to 80% without affecting specificity. The third criteria regarding greater than 5 mm of discordance were chosen rather arbitrarily. The modified criteria change 5 mm to greater than 25% of the downward QRS deflection.

Criteria 3 is modified as follows: Discordant ST elevation greater than 25% of downward QRS deflection in a negative QRS complex (2 points)

Definition of Terms

Concordant: Means QRS and T wave go the same direction. 

Discordant: Means QRS is opposite direction of T wave.

Positive QRS Complex: Net voltage of QRS goes upward from baseline.

Negative QRS Complex: Net voltage of QRS goes downward from baseline. [3][4]

Enhancing Healthcare Team Outcomes

LBBB may be encountered in clinical practice by the nurse practitioner, primary care provider, emergency department physician and the internist. While LBBB by itself may be a normal occurrence, it is important to refer these patients to a cardiologist to determine that there is no underlying cardiac pathology.

In otherwise healthy individuals, LBBB does not confer any specific or additional risk.  Mortality hazard ratio (HR) for LBBB is only 1.3 of normal. However, in patients with new onset, LBBB mortality HR is greater than 10-times normal.[1] Specific at-risk populations of patients with LBBB are those who are presenting with chest pain and have new-onset LBBB which should be considered equivalent to ST-segment elevation.[2] In patients with heart failure, the presence of left bundle branch block is associated with increased cardiovascular outcomes and mortality. 

The cardiology nurse should educate the patient on the significance of LBBB. In the US, patients with LBBB are not allowed to pilot an aircraft or other heavy equipment.[9][8]


References

[1] Left bundle-branch block--pathophysiology, prognosis, and clinical management., Francia P,Balla C,Paneni F,Volpe M,, Clinical cardiology, 2007 Mar     [PubMed PMID: 17385703]
[2] 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines., O'Gara PT,Kushner FG,Ascheim DD,Casey DE Jr,Chung MK,de Lemos JA,Ettinger SM,Fang JC,Fesmire FM,Franklin BA,Granger CB,Krumholz HM,Linderbaum JA,Morrow DA,Newby LK,Ornato JP,Ou N,Radford MJ,Tamis-Holland JE,Tommaso CL,Tracy CM,Woo YJ,Zhao DX,Anderson JL,Jacobs AK,Halperin JL,Albert NM,Brindis RG,Creager MA,DeMets D,Guyton RA,Hochman JS,Kovacs RJ,Kushner FG,Ohman EM,Stevenson WG,Yancy CW,, Journal of the American College of Cardiology, 2013 Jan 29     [PubMed PMID: 23256914]
[3] 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., Sgarbossa EB,Pinski SL,Barbagelata A,Underwood DA,Gates KB,Topol EJ,Califf RM,Wagner GS,, The New England journal of medicine, 1996 Feb 22     [PubMed PMID: 8559200]
[4] Validation of the modified Sgarbossa criteria for acute coronary occlusion in the setting of left bundle branch block: A retrospective case-control study., Meyers HP,Limkakeng AT Jr,Jaffa EJ,Patel A,Theiling BJ,Rezaie SR,Stewart T,Zhuang C,Pera VK,Smith SW,, American heart journal, 2015 Dec     [PubMed PMID: 26678648]
[5] The prevalence and incidence of left bundle branch block in ambulant patients with chronic heart failure., Clark AL,Goode K,Cleland JG,, European journal of heart failure, 2008 Jul     [PubMed PMID: 18501670]
[6] LBBB: State-of-the-Art Criteria., Nikoo MH,Aslani A,Jorat MV,, International cardiovascular research journal, 2013 Jun     [PubMed PMID: 24757618]
[7] 2013 ACCF/AHA guideline for the management of heart failure: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines., Yancy CW,Jessup M,Bozkurt B,Butler J,Casey DE Jr,Drazner MH,Fonarow GC,Geraci SA,Horwich T,Januzzi JL,Johnson MR,Kasper EK,Levy WC,Masoudi FA,McBride PE,McMurray JJ,Mitchell JE,Peterson PN,Riegel B,Sam F,Stevenson LW,Tang WH,Tsai EJ,Wilkoff BL,, Journal of the American College of Cardiology, 2013 Oct 15     [PubMed PMID: 23747642]
[8] Dambrink JH,Dambrink JH, Left bundle branch block and private pilot licensing. Aviation, space, and environmental medicine. 2003 Dec;     [PubMed PMID: 14692475]
[9] Ezzeddine FM,Dandamudi G, Updates on His bundle pacing: The road more traveled lately. Trends in cardiovascular medicine. 2018 Oct 9;     [PubMed PMID: 30344079]