I44.7

Left bundle branch block (I44.7): ECG criteria, causes, heart failure and CRT, and LBBB in myocardial infarction.

Left bundle branch block (LBBB, ICD-10 I44.7) is a block of conduction in the left bundle branch. The left ventricle is then activated slowly and late from the right side, through the muscle rather than the fast conduction system, so the left ventricle contracts after the right one and the two ventricles are poorly synchronised (dyssynchrony). On the ECG the QRS is wide, at least 120 ms, with a broad notched R wave in the left-sided leads. LBBB is usually a sign of underlying heart disease and can itself worsen heart function.

ICD-10 I44.7Bundle branch blockHeart failure

QRS duration≥ 120 ms

Leads I, aVL, V5–V6broad notched R, no septal q

ST–Topposite to the QRS (discordant)

Next testechocardiography

Figure 1. Left: normal QRS in V6. Right: complete LBBB — QRS of 120 ms or more, broad notched R wave without q, and secondary ST–T changes opposite to the QRS.

Causes

Hypertension, coronary artery disease, dilated and other cardiomyopathies, aortic stenosis and aortic valve procedures, myocarditis, age-related fibrosis of the conduction system. LBBB can also be rate-dependent (appearing only at faster heart rates).

Clinical significance

Heart failure: LBBB is common in heart failure and worsens pumping through dyssynchrony. In patients with heart failure, reduced ejection fraction (35% or less) and LBBB with QRS of 150 ms or more despite optimal medicines, cardiac resynchronisation therapy (CRT) improves symptoms and survival.
Myocardial infarction: LBBB hides the usual ECG signs of infarction. A patient with LBBB and symptoms of acute ischaemia is managed as a possible STEMI; specific criteria (for example Sgarbossa) help recognise infarction.
Conduction: LBBB may progress to complete AV block, especially with syncope or alternating bundle branch block.

Call emergency services

for chest pain, severe breathlessness or fainting, especially if LBBB is new.

References

Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances. Circulation. 2009;119(10):e235–e240. doi:10.1161/CIRCULATIONAHA.108.191095
Glikson M, Nielsen JC, Kronborg MB, et al. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. Eur Heart J. 2021;42(35):3427–3520. doi:10.1093/eurheartj/ehab364
Sgarbossa EB, Pinski SL, Barbagelata A, et al. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. N Engl J Med. 1996;334(8):481–487. doi:10.1056/NEJM199602223340801

This article is for general information and does not replace a consultation with a doctor. Diagnosis and treatment must be decided by a physician on the basis of symptoms, examination and tests.

Published on 24 March 2019