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    2.1
    Home > ECG findings

    2.1

    Minnesota Code 2-1: QRS axis between −30° and −90°; causes (left anterior fascicular block, LVH, inferior MI) and when it matters.

    Code 2.1 — Minnesota Code 2-1: left axis deviation. The electrical axis of the QRS complex in the frontal plane shows the average direction in which the ventricles are activated. Code 2-1 is assigned when this axis lies between −30° and −90°, i.e. it is turned markedly to the left and upward. The most common cause is left anterior fascicular block; other causes include left ventricular hypertrophy, inferior myocardial infarction and some congenital heart defects.

    Minnesota Code 2QRS axisLeft anterior fascicular block
    Normal axis−30° to +90°
    Code 2-1−30° to −90°
    Quick checkQRS + in I, − in II and aVF
    Most common causeleft anterior fascicular block

    How the axis is determined

    The six limb leads look at the heart from different directions in the frontal plane (hexaxial reference system). The QRS axis points towards the lead in which the QRS is most positive and is perpendicular to the lead in which it is equiphasic. A practical rule: if the QRS is positive in lead I but predominantly negative in leads II and aVF, the axis is more leftward than −30°.

    Hexaxial diagram of the frontal plane with normal axis sector from minus 30 to plus 90 degrees, left axis deviation from minus 30 to minus 90 degrees, right axis deviation from plus 90 to 180 degrees and extreme axis I 0°II +60°aVF +90°III +120° aVL −30°aVR −150°±180°−90° Normal axis: −30° to +90° Left axis (code 2-1): −30° to −90° Right axis (code 2-2): +90°/+120° to 180° Extreme axis: −90° to ±180° Red arrow: axis ≈ −30°/−45° I positive, II and aVF negative
    Figure 1. The frontal-plane (hexaxial) reference system. Left axis deviation means the mean QRS vector points upward and to the left, beyond −30°.

    Causes

    CauseComment
    Left anterior fascicular block (LAFB)Most common; axis usually −45° to −90°, qR in I/aVL, rS in II, III, aVF (see code 7.6)
    Left ventricular hypertrophyOften moderate leftward shift, with high R voltage
    Inferior myocardial infarctionQ waves in II, III, aVF move the axis to the left
    Left bundle branch block, ventricular pacing, WPW patternAbnormal activation sequence
    Congenital heart diseaseOstium primum atrial septal defect, tricuspid atresia
    Body habitusObesity, pregnancy, ascites (elevated diaphragm) — usually mild shift

    Clinical significance

    Isolated left axis deviation without symptoms is often a benign finding, especially in older people. However, it can be the first sign of conduction-system disease or hypertrophy. In combination with right bundle branch block (bifascicular block) or a prolonged PR interval it may indicate a risk of progression to higher-grade AV block.

    When to see a doctor

    Arrange a check-up if the axis deviation is new, or if it is accompanied by high blood pressure, shortness of breath, dizziness, fainting or other ECG changes. An echocardiogram is usually recommended to exclude hypertrophy and structural disease.

    References

    1. 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
    2. 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

    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