Real-time PC-based system for dynamic beat-to-beat QT-RR analysis

A real-time analysis (RTA) system, based on a personal computer with a digi tal signal processor card (DSP) was developed. The system extracts and save s the QT and RR intervals from an incoming ECG signal sampled at 1 kHz. The method of defining the QT and RR intervals is based on performing multiple cross-correlations that enables rejection of artifacts from the analysis. The relationship between the RR and the Qr intervals is found using the fol lowing general formula QT(i) = cRR(i-1)(b). Linear regression is performed on the logarithms of QT and RR measurements obtained to estimate a constant (a = logc) and a slope (b), reflecting the dynamic change of the QT interv als. Having these two values, the dynamic QT extrapolated to a heart period of 1 s (QTcd) was calculated. The system also performs spectral analysis o f the intervals and dynamic QT-RR relation-analysis. The system was evaluat ed oil recordings from 10 infants aged 4 to 24 weeks. The QT/RR computerize d measuring device used in the present study answers to the requirements fo r precise dynamic beat-to-beat QT measurement. its sampling rate is high an d can achieve a real millisecond-precision without the need of interpolatio n methods. The measurements are performed on-line, at the time of the actua l recording. Results appear immediately and a measure of dynamic QT behavio r can be easily obtained within minutes. The computerized system with the d ynamic QT-RR measurements may provide a simple and accurate tool for testin g drug treatment and effects of other interventions for cardiac disorders a nd arrhythmia risk. (C) 1999 Academic Press.