A simple procedure for estimation of the spatial QRS/T angle from the standard 12-lead electrocardiogram.

The spatial QRS/T angle has been identified as a strong predictor of adverse cardiac events. Mean QRS and T amplitudes from X, Y, and Z leads generated by a matrix transformation method are often used to calculate the QRS/T angle (QRS/T(matrix)). Many investigators find this procedure cumbersome. We used electrocardiographic data files of 14881 men and women aged 45 to 65 years from the Atherosclerosis in Communities study to derive a simple formula for estimated spatial QRS/T angle (QRS/T(simple)). QRS/T(simple) is calculated as the inverse cosine between the mean QRS and T vectors, which are approximated by 3 QRS(net) and T(net) amplitudes for each vector. QRS/T(simple) explained 79% of the variance of QRS/T(matrix) (r = 0.89). Using sex-specific thresholds, QRS/T(simple) detected abnormally wide QRS/T(matrix) values with a sensitivity of 91% and specificity of 88%. It is concluded that this simple method may provide a satisfactory substitute for QRS/T from the matrix transformation method.