Table 1.

Electrocardiographic Measures of Repolarization Heterogeneity

ECG Measure	Definition
Principal component analysis of the T wave	Ratio of the second to first eigenvalues of the spatial T‐wave vector generated from the 12‐lead digital ECG
QRS‐T angle	Adding the mean vector representing all of the electrical forces produced by depolarization and repolarization. This is accomplished by forming a parallelogram using the QRS vector and the T‐wave vector as its sides; the diagonal of the figure is the spatial ventricular gradient.
QT dispersion	Difference in ms between maximal and minimal QTc intervals from between 3 and 6 leads in a simultaneous 12‐lead ECG
Simplified QRS‐T angle	Absolute difference between the QRS and T‐wave axes on the 12‐lead ECG
T peak T end	Time in ms between the peak of the T wave to the end of the T wave, as defined by the intersection of the tangent to the down slope of the T wave and the isoelectric line. Typically measured in V5
T‐wave area (total and late)	Area between the curve and baseline from J point to T end and T peak to T end, respectively
T‐wave residuum	Absolute value of the sum of the squares of the fourth to eighth eigenvalues of the reconstructed T wave after singular value decomposition
T‐wave loop dispersion	Dissimilarities between the T‐wave shapes in individual leads, based on reconstruction vectors of individual ECG leads
Total cosine R‐to‐T	Calculating cosine values between the 3‐dimensional R‐ and T‐wave loop vectors

ECG indicates electrocardiogram.