An algorithm for automatic beat-to-beat measurement of the QT-interval

An algorithm for automatic measurement of the QT-interval is described. The algorithm consists of two passes. In the first pass the differentiated signal is passed through an existing QRS-detector which is modified to detect the end of T-wave. The pointers found for Q-onset and T-end are used for creation of a filter, which estimates the low frequency part of the signal. Subsequently this estimate is subtracted from the original signal where after the same algorithm is applied for the second pass. Validation was done on recordings of 20 patients; 1861 triple beats were randomly selected and eyeball measurements of the QT duration were performed by two experienced cardiologists. The difference of the QT-interval between the cardiologists and the algorithm was 3.64 msec (n.s.). It is concluded that the algorithm reliably calculates the QT-interval, even if major baseline wander is present.<>