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    3.1
    Home > ECG findings

    3.1

    Novacode 3.1: complete left bundle branch block — QRS ≥ 120 ms, broad notched R in I, aVL, V5–V6; causes, risks and why it needs evaluation.

    Code 3.1 (Novacode NC-3.1) — complete left bundle branch block (LBBB). In LBBB the electrical impulse cannot travel down the left bundle branch. The right ventricle is activated normally, and the impulse then spreads slowly through the muscle to the left ventricle. The QRS complex becomes wide (≥ 120 ms), with broad, notched R waves in the left leads and ST-T changes opposite to the QRS. In the Minnesota Code the same finding is coded 7-1-1.

    Novacode 3Ventricular conductionLeft bundle branch block
    QRS duration≥ 120 ms
    Leads I, aVL, V5–V6broad notched R, no q
    V1QS or rS
    Minnesota Code7-1-1

    ECG criteria (AHA/ACCF/HRS)

    • QRS duration ≥ 120 ms in adults
    • Broad, notched or slurred R waves in I, aVL, V5, V6; occasional RS pattern in V5–V6
    • Absent q waves in I, V5 and V6
    • R-peak time > 60 ms in V5 and V6
    • ST and T waves usually opposite in direction to the QRS (appropriate discordance)
    Normal narrow QRS in lead V6 compared with complete left bundle branch block: wide notched R wave and discordant ST depression with inverted T wave Normal V6 QRS ≈ 90 ms QRS 90 ms LBBB QRS ≥ 120 ms, notched R QRS 150 ms
    Figure 1. Left: normal QRS in V6. Right: complete LBBB — QRS ≥ 120 ms, broad notched ('M-shaped') R wave without q, and secondary ST-T changes opposite to the QRS.

    Causes and significance

    LBBB is uncommon in healthy young people and usually indicates underlying heart disease: hypertension with left ventricular hypertrophy, coronary artery disease, cardiomyopathy, aortic valve disease, or degenerative fibrosis of the conduction system in older age. LBBB makes the left ventricle contract in an uncoordinated way (dyssynchrony), which can worsen heart function. In people with heart failure and wide LBBB, cardiac resynchronisation therapy (a special pacemaker) can improve symptoms and survival.

    LBBB and myocardial infarction

    LBBB distorts the ST segment and can mask an acute heart attack. Special criteria (Sgarbossa) are used to recognise infarction in the presence of LBBB — see code 3.11. A new LBBB together with chest pain is treated as a possible acute coronary syndrome.

    Seek urgent care

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

    Planned evaluation

    Known LBBB requires an echocardiogram and cardiology assessment to look for structural heart disease, even without symptoms.

    References

    1. 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
    2. Rautaharju PM, Park LP, Chaitman BR, Rautaharju F, Zhang ZM. The Novacode criteria for classification of ECG abnormalities and their clinically significant progression and regression. J Electrocardiol. 1998;31(3):157–187.
    3. 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