Medical & Biological Engineering & Computing

, Volume 37, Issue 1, pp 71–79

QT interval analysis on ambulatory electrocardiogram recordings: a selective beat averaging approach


    • Service de CardiologieHôpital Lariboisière
  • P. Maison-Blanche
    • Service de CardiologieHôpital Lariboisière
  • R. Childers
    • Section of CardiologyThe University of Chicago Medical Center
  • P. Coumel
    • Service de CardiologieHôpital Lariboisière
Physiological Signal Analysis

DOI: 10.1007/BF02513269

Cite this article as:
Badilini, F., Maison-Blanche, P., Childers, R. et al. Med. Biol. Eng. Comput. (1999) 37: 71. doi:10.1007/BF02513269


A computerised method for the analysis of QT intervals in ambulatory ECG recordings is presented. This approach is based on selective beat averaging which allows one to process P-QRS-T complexes together with the environment that characterises them. Long-term autonomic nervous system influences are accounted for by separating the analysis over different circadian periods. Effects of QT recovery time are taken into account by requiring a stable heart rate preceding each beat to be averaged. Before averaging, beats are resampled and realigned with respect to the R-wave peak estimated by parabolic interpolation. Averaged ECG templates are then analysed with an algorithm which automatically detects QRS complex and T-wave features. Repolarisation analysis is based on first and second derivatives of lowpass filtered ECG (recursive Butterworth filter). The QT/RR relationship and the circadian QT variation at identical heart rate were analysed in 14 normal individuals. When performed at stable heart rate conditions and when confined to well-defined circadian periods, the QT/RR relationship was strongly linear (r=0.95±0.06); in addition, the slope of this relation changed between day and night (respectively, 0.197±0.07 and 0.139±0.03, p<0.01). The range of circadian QT variation at identical heart rate was approximately 20 ms for both males and females.


QT intervalAmbulatory ECG recordingsSelective beat averagingQT/RR relation
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© IFMBE 1999