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    5.3
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    5.3

    Minnesota Code 5-3: flat, shallow negative or biphasic T wave — a minor repolarisation change and its common causes.

    Code 5.3 — Minnesota Code 5-3: flat, shallow negative or biphasic T wave. The T wave is flat (isoelectric), slightly negative, or biphasic with a negative part smaller than 1.0 mm, in a lead where it should normally be clearly upright. This is a minor repolarisation abnormality. It is often non-specific, but it may also accompany ischaemia, hypertrophy, electrolyte disorders or the effect of medicines.

    Minnesota Code 5Flat T waveMinor ST-T change
    T waveflat, or negative < 1.0 mm
    Or biphasicnegative phase < 1.0 mm
    Classminor abnormality
    Novacodepart of NC-5.8
    Normal upright T wave compared with a flat T wave and a biphasic T wave with a small negative part Normal T T upright Flat T code 5-3 Biphasic T negative phase < 1 mm
    Figure 1. Left: normal T wave. Middle: flat T wave. Right: biphasic T wave with a small negative phase under 1 mm. Both right-hand patterns correspond to Minnesota 5-3.

    Possible causes

    • Low potassium or magnesium (often with prominent U waves)
    • Medicines: digoxin, antiarrhythmics, antidepressants, antipsychotics
    • Myocardial ischaemia, left ventricular hypertrophy, cardiomyopathy
    • Hypothyroidism, pericardial effusion, obesity, emphysema (low voltage)
    • Hyperventilation, eating, posture changes, anxiety
    • Normal variant, especially in lead III or aVL

    Clinical significance

    An isolated flat T wave rarely means serious disease. Its significance increases when the change is new, occurs in several leads, accompanies ST depression or appears in a person with symptoms or heart disease. In epidemiological studies, minor ST-T abnormalities such as these have been linked to a moderately higher risk of cardiovascular events and are therefore a reason to check risk factors.

    What to do

    Discuss the ECG with your doctor at a scheduled visit. Blood potassium and magnesium tests and a review of medications are often useful. Seek urgent care if you have chest pain, breathlessness or fainting.

    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. 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

    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