Cardiac repolarization analysis: Immediate response

The reproducibility of QT parameters was tested on data recorded in subjects undergoing graded head-up tilt. Two QT detection algorithms were tested: D1 - on a beat to beat basis and D2 - on a 10-beats average basis. Relative irreproducibility, defined as STD/mean, in the case of D1 detection was 0.7, 6.3, 10 [%] for QTc, QT/RR slope and QT restitution respectively. With D2 detection it was 0.7, 6.3, and 59 [%] respectively. Conclusion: QT immediate response, i.e. the QT restitution, is reproducible parameter with D1 detection. D2 detection eliminates any information about QT restitution and does not increase the reproducibility of QT slow properties, as QTc and QT/RR slope.