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7.11

Minnesota Code 7-1-1: complete left bundle branch block — criteria, why other codes are suppressed, causes and evaluation.

Code 7.11 — Minnesota Code 7-1-1: complete left bundle branch block. The Minnesota Code assigns 7-1-1 when the QRS duration is 0.12 s (120 ms) or more in a majority of beats in the limb leads, and the R-peak time in I, aVL, V5 or V6 is prolonged (≥ 0.06 s) with the typical broad, notched R wave. The left bundle branch is blocked, so the left ventricle is activated late and slowly through the muscle. When this code is present, Q-wave, ST and T codes are not assigned, because LBBB itself changes these components.

Minnesota Code 7Left bundle branch blockWide QRS

QRS duration≥ 120 ms

R-peak time≥ 60 ms in I, aVL, V5, V6

Suppressescodes 1, 4, 5

NovacodeNC-3.1 (code 3.1)

Figure 1. Left: normal QRS in V6. Right: complete LBBB — QRS ≥ 120 ms, broad notched R wave, prolonged R-peak time and discordant ST-T (Minnesota 7-1-1).

Why other codes are suppressed

In LBBB the whole sequence of ventricular activation is changed. Q waves may disappear or appear, and ST and T are shifted in the direction opposite to the QRS. Standard criteria for infarction and ischaemia therefore do not apply; special criteria (Sgarbossa) are used instead, as described for code 3.11.

Causes

Hypertension and left ventricular hypertrophy
Coronary artery disease, myocardial infarction
Dilated cardiomyopathy, myocarditis, aortic valve disease
Degenerative disease of the conduction system; after aortic valve procedures (TAVI)

Clinical significance

LBBB is rare in healthy people. When it is found, an echocardiogram is recommended to look for structural heart disease and left ventricular dysfunction. Dyssynchronous contraction caused by LBBB can worsen heart failure. In selected patients with reduced ejection fraction and wide LBBB, cardiac resynchronisation therapy improves symptoms and survival.

Seek emergency care

if LBBB is new or accompanied by chest pain, breathlessness, fainting or a very slow pulse.

References

Prineas RJ, Crow RS, Zhang ZM. The Minnesota Code Manual of Electrocardiographic Findings. 2nd ed. London: Springer; 2010. doi:10.1007/978-1-84882-778-3
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
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. ECG findings must be interpreted by a physician together with symptoms and other tests.

Published on 14 May 2019

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