QT interval measurement: What can we really expect?

This study is an effort of measuring QT interval with an automatic computerized algorithm. The aims of the algorithm are consistency as well as accuracy. The general methodology adopted in this algorithm is to seek more consistent QT interval measurement by using multi- lead and multi-beat information from a given segment of ECG. A representative beat is generated from selected segment of each lead, and then a composite beat is formed by the representative beats of all independent leads. The end result of the QT measure is so-called global QT measurement, which usually catches the longest QT interval in multiple leads. Individual lead QT interval was estimated by using the global measurement as a starting point, and then adapted to the signal of the particular lead and beat. In general, beat-by-beat QT measurement is more prone to noise, therefore less reliable than the global estimation. It is usually difficult to know if difference of beat-by-beat QT interval is due to true physiological change or noise fluctuation. In the study, we tested the algorithm by using clinical databases and also a modeling based simulation signals. The modeling approach provided a more objective test for the estimation. The modeling approach allowed us to evaluated the QT measurement vs. Action potential duration (APD). The results show that the mean error between the algorithm and cardiologist QT intervals is 3.95+ 5.5 msec based on a large clinical trial database consisting of 15910 ECGs. The results also show that the correlation coefficient between QT intervals and maximum APD is 0.99.