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    7.7
    Home > ECG findings

    7.7

    Minnesota Code 7-7: left posterior fascicular block — right axis deviation after excluding other causes; significance.

    Code 7.7 — Minnesota Code 7-7: left posterior fascicular block (LPFB, left posterior hemiblock). When the posterior fascicle of the left bundle branch is blocked, the left ventricle is activated first from the anterior fascicle, upward and to the left, and then downward and to the right. The ECG shows right axis deviation (+90° to +180°) with rS in I and aVL and qR in III and aVF. The QRS remains under 120 ms. LPFB is much rarer than LAFB, because the posterior fascicle is thick and has a dual blood supply.

    Minnesota Code 7Fascicular blockRight axis deviation
    QRS axis+90° to +180°
    I, aVLrS
    III, aVFqR
    QRS duration< 120 ms

    ECG criteria (AHA/ACCF/HRS)

    • Frontal-plane axis between +90° and +180° in adults
    • rS pattern in I and aVL; qR pattern in III and aVF
    • QRS duration < 120 ms
    • Other causes of right axis deviation must be excluded: right ventricular hypertrophy, lung disease, lateral infarction, vertical heart position in thin young people
    Lead I with rS pattern and lead III with qR pattern typical of left posterior fascicular block I rS III qR
    Figure 1. Typical LPFB: rS in lead I (left) and qR in lead III (right), corresponding to a QRS axis of about +120°.

    Clinical significance

    Because the posterior fascicle is robust, isolated LPFB usually indicates significant heart disease: coronary artery disease, hypertension, cardiomyopathy or degenerative conduction disease. LPFB combined with RBBB is a form of bifascicular block that carries a risk of progression to complete AV block. The diagnosis is made only after excluding other causes of right axis deviation, which often requires echocardiography.

    Seek urgent care

    if you have fainting, near-fainting, a very slow pulse, chest pain or breathlessness.

    Planned evaluation

    A cardiology assessment and echocardiography are recommended, especially if LPFB is new or combined with RBBB or a prolonged PR interval.

    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