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    T wave: ventricular repolarisation, normal direction by lead, peaked, inverted and flat T waves and alternans.

    The T wave follows the ST segment and reflects repolarisation of the ventricles, the electrical recovery that prepares them for the next beat. Repolarisation proceeds in roughly the opposite direction to depolarisation, so in most leads the T wave points the same way as the main QRS deflection. The time from the start of the QRS to the peak of the T wave corresponds to the absolute refractory period; the second half of the T wave is the vulnerable period, when an extra stimulus can trigger ventricular fibrillation.

    ECGRepolarisationElectrolytes
    UprightI, II, V3–V6
    Inverted (normal)aVR
    Variable (normal)III, aVL, aVF, V1
    Shapeasymmetric, slow upstroke
    One ECG beat with the T wave highlighted after the ST segment J point P PR seg. QRS ST seg. T PR interval ST interval QT interval
    Figure 1. The T wave (highlighted) is the rounded wave after the ST segment; its first part rises more slowly than its last part falls.

    Abnormal T waves

    • Tall, narrow, peaked T: hyperkalaemia; broad tall "hyperacute" T waves can be the earliest sign of myocardial infarction
    • Inverted T: myocardial ischaemia or evolving infarction, Wellens pattern in V2–V3 (critical narrowing of the left anterior descending artery), left ventricular hypertrophy, cardiomyopathy, pulmonary embolism (V1–V4), myocarditis, after tachycardia; secondary to bundle branch block or pacing; deep giant inversions after brain haemorrhage. Inverted T in V1–V3 is normal in children (juvenile pattern).
    • Flat T, often with a prominent U wave: hypokalaemia, hypothyroidism, medicines
    • T-wave alternans: beat-to-beat change in T amplitude or shape, a marker of electrical instability and arrhythmia risk
    • Long Tpeak–Tend interval: increased dispersion of repolarisation, associated with arrhythmia risk
    Normal T wave compared with a tall peaked T wave of hyperkalaemia and with an inverted T wave Normal T upright, asymmetric Peaked T hyperkalaemia Inverted T ischaemia and others
    Figure 2. Left: normal T wave. Middle: tall, narrow, peaked T wave, as in hyperkalaemia. Right: inverted T wave, as in ischaemia.
    Seek emergency care

    for chest pain, breathlessness, fainting or palpitations together with new T-wave changes, and for peaked T waves in a person with kidney disease or on potassium-raising medicines, because severe hyperkalaemia can stop the heart.

    References

    1. Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241–e250. doi:10.1161/CIRCULATIONAHA.108.191096
    2. Thygesen K, Alpert JS, Jaffe AS, et al. Fourth universal definition of myocardial infarction (2018). Eur Heart J. 2019;40(3):237–269. doi:10.1093/eurheartj/ehy462

    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 7 July 2019