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A simple procedure for estimation of the spatial QRS/T angle from the standard 12-lead electrocardiogram
Pentti M Rautaharju1, Ronald J Prineas, Zhu-Ming Zhang
1Epicare Center, Division of Public Health Sciences, Wake Forest University School of Medicine, Winston Salem, NC, USA. penttir@bellsouth.net
Abstract:
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.
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