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    9.5
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    9.5

    Minnesota Code 9-5: tall T waves over 12 mm — hyperkalaemia, hyperacute infarction and benign variants.

    Code 9.5 — Minnesota Code 9-5: high-amplitude T waves. The T wave is more than 12 mm (1.2 mV) tall in at least one lead. The T wave is the most variable component of the ECG. Tall T waves can be a normal variant in young people and athletes, but they can also signal high blood potassium (hyperkalaemia) or the earliest "hyperacute" phase of a myocardial infarction. Both are emergencies.

    Minnesota Code 9Tall T wavesHyperkalaemia
    CriterionT > 12 mm
    Hyperkalaemianarrow, peaked "tent" T
    Hyperacute MIbroad, tall, symmetric T
    Benignearly repolarisation, athletes
    Normal T wave compared with a narrow peaked T wave of hyperkalaemia and a broad hyperacute T wave of early myocardial infarction Normal T normal Hyperkalaemia narrow peaked T Hyperacute T broad tall T
    Figure 1. Left: normal T. Middle: narrow, sharply peaked ('tented') T wave typical of hyperkalaemia. Right: broad, tall, symmetric hyperacute T wave of the earliest phase of a myocardial infarction.

    Causes

    CauseFeatures
    HyperkalaemiaNarrow-based, peaked T; with rising potassium: P flattening, PR prolongation, QRS widening, risk of cardiac arrest. Kidney failure, potassium-sparing drugs, ACE inhibitors, tissue breakdown
    Hyperacute phase of MIBroad, tall, symmetric T in a coronary territory, minutes after artery occlusion; may precede ST elevation
    de Winter patternUp-sloping ST depression with tall symmetric T in V1–V6 — proximal LAD occlusion
    Normal variantsEarly repolarisation, young men, athletes, high vagal tone
    Left ventricular hypertrophy, LBBBTall T in V1–V3 discordant with deep S waves

    Clinical significance

    The interpretation of tall T waves depends heavily on the clinical situation. In a person with kidney disease, weakness or on potassium-raising medication, blood potassium must be checked without delay. In a person with chest pain, tall T waves may be the first sign of an occluded coronary artery; serial ECGs over a few minutes are essential.

    Seek emergency care

    if tall T waves are found together with chest pain, palpitations, marked weakness, or with known kidney failure or medicines that raise potassium.

    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. de Winter RJ, Verouden NJW, Wellens HJJ, Wilde AAM. A new ECG sign of proximal LAD occlusion. N Engl J Med. 2008;359(19):2071–2073. doi:10.1056/NEJMc0804737
    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