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    7.6
    Home > ECG findings

    7.6

    Minnesota Code 7-6: left anterior fascicular block — axis −45° to −90°, qR in aVL; causes and significance.

    Code 7.6 — Minnesota Code 7-6: left anterior fascicular block (LAFB, left anterior hemiblock). The left bundle branch divides into an anterior and a posterior fascicle. When the anterior fascicle is blocked, the impulse spreads first to the lower and back walls of the left ventricle, and only then upward and to the left. The result is a marked left axis deviation (−45° to −90°) with a QRS that is only slightly widened (< 120 ms).

    Minnesota Code 7Fascicular blockLeft axis deviation
    QRS axis−45° to −90°
    I, aVLqR
    II, III, aVFrS
    QRS duration< 120 ms

    ECG criteria (AHA/ACCF/HRS)

    • Frontal-plane axis between −45° and −90°
    • qR pattern in lead aVL
    • R-peak time in aVL ≥ 45 ms
    • QRS duration < 120 ms
    Lead aVL with qR pattern and lead III with rS pattern typical of left anterior fascicular block aVL qR III rS
    Figure 1. Typical LAFB: qR in lead aVL (left) and rS in lead III (right), which correspond to a QRS axis of about −60°.

    Causes and significance

    The anterior fascicle is thin and supplied mainly by the left anterior descending artery, so it is the most vulnerable part of the conduction system. LAFB is common in older people and may be associated with hypertension, coronary artery disease, cardiomyopathy, aortic valve disease or degenerative fibrosis. Isolated LAFB does not need treatment by itself, but in some cohort studies it has been associated with higher cardiovascular risk. The combination of LAFB and RBBB (bifascicular block, Minnesota 7-8) indicates more extensive conduction disease. Combined with a prolonged PR interval or fainting, it can signal a risk of higher-degree AV block.

    Interpretation tip

    LAFB can mask or imitate inferior or anterior Q waves and can affect LVH voltage criteria, so the doctor takes it into account when reading the rest of the ECG.

    Seek urgent care

    if LAFB is accompanied by fainting, near-fainting, a very slow pulse or chest pain.

    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. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628
    3. 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

    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