An alternative decision rule for threshold based T-wave measurement algorithms based on second derivative extrema

QT interval is a surface ECG measure which has been the subject of great research interest. Usually, a prolongation of the QT interval beyond the normal value is associated with bad cardiac prognosis. In this paper we revisit the wavelet transform based method. Rather than using a threshold related or the highest inflection point of the derivative, we use the extreme on the second derivative which appears ahead of the inflexion point. This rule differs from the thresholds one in its simplicity of application and its potential for real time analysis. The algorithm detects the end of the T-wave by using the first and second derivative on the fifth scale. Results for the T wave obtained in simulations give a mean error of -6.73 +/- 14.5 ms (-7.80 +/- 21.04 ms when adding white noise in a SNR of approximately 4 dB) whereas results in Physionetpsilas QTDB give (-1.22 +/- 38.85 ms) in the case of T end locations. The results for the threshold method were (-1.6 +/- 18.1 ms).