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    T-wave morphology analysis: TCRT, morphology dispersion and PCA ratio for repolarisation and risk assessment.

    T-wave morphology analysis describes the shape of the T wave with numbers, rather than by eye. Mathematical methods (singular value decomposition, principal component analysis) are applied to all 12 ECG leads together. They reconstruct the spatial direction of the depolarisation and repolarisation wavefronts and measure how uniform repolarisation is. Increased heterogeneity of repolarisation creates a substrate for ventricular arrhythmias. These parameters help to stratify risk after myocardial infarction, in heart failure and in cardiomyopathies.

    ECGRepolarisationRisk stratification
    TCRTangle between QRS and T wavefronts
    TMDT-wave morphology dispersion
    PCA ratiocomplexity of the T wave
    Method12-lead, computer analysis

    Main parameters

    • Total cosine R-to-T (TCRT): the cosine of the spatial angle between the main depolarisation (QRS) and repolarisation (T) vectors. Normally the two point in similar directions, so TCRT is positive (close to +1). Values near zero or negative mean that repolarisation runs in an abnormal direction.
    • T-wave morphology dispersion (TMD): how different the T-wave shape is between leads. A higher value means more uneven repolarisation.
    • Principal component analysis (PCA) ratio: the share of the T-wave signal that cannot be explained by a single main component. A higher ratio means a more complex, less uniform T wave.
    • T-wave loop parameters: the shape and width of the T-wave loop in three dimensions (vectorcardiography)
    Normal T wave compared with a flattened T wave and a biphasic T wave, examples of abnormal repolarisation morphology Normal T smooth, uniform Flattened T low amplitude Biphasic T two phases
    Figure 1. Visual examples of T-wave shapes: normal (left), flattened (middle) and biphasic (right). Morphology analysis quantifies such changes across all 12 leads at once.

    Clinical significance

    In patients after myocardial infarction, abnormal TCRT predicted adverse cardiac events independently of other risk factors such as left ventricular ejection fraction. Abnormal values are also found in hypertrophic and dilated cardiomyopathy, heart failure and long QT syndrome. The values depend on the recording and analysis software, so there are no universal normal limits; results should be compared with the reference values of the method used, and interpreted together with ejection fraction, QT, heart rate variability and clinical data.

    Why it matters

    Visual reading of the T wave is subjective. Quantitative analysis can detect subtle repolarisation abnormalities before they become obvious, but it is a research and risk-assessment tool and does not diagnose a specific disease by itself.

    References

    1. Zabel M, Acar B, Klingenheben T, Franz MR, Hohnloser SH, Malik M. Analysis of 12-lead T-wave morphology for risk stratification after myocardial infarction. Circulation. 2000;102(11):1252–1257.
    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 6 July 2019