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. 2004 Jan;9(1):3-11.
doi: 10.1111/j.1542-474x.2004.91510.x.

Beat-to-beat QT dynamics in healthy subjects

Berit T Jensen  1 , Charlotte E Larroude, Lars P Rasmussen, Niels-Henrik Holstein-Rathlou, Michael V Hojgaard, Erik Agner, Jørgen K Kanters
Affiliations

Beat-to-beat QT dynamics in healthy subjects

Berit T Jensen et al. Ann Noninvasive Electrocardiol. 2004 Jan.

Abstract

Background: Measures of QT dynamics express repolarization abnormalities that carry prognostic information, but the reproducibility of beat-to-beat QT dynamics has never been established. The QT interval is prolonged at night, but how the circadian rhythm and heart rate influence the dynamic QT measurements is still unsettled. The aims of the present study were: (1) to describe the reproducibility of beat-to-beat QT dynamics with respect to intrasubject, between-subject, and between-observer variability and (2) to describe the normal range, circadian variation, and heart rate dependence of QT dynamics.

Methods: Ambulatory Holter recordings were performed three times on 20 healthy volunteers and were analyzed by two experienced cardiologists. Slope and intercept of the QT/RR regression, the variability of QT and R-R intervals expressed as the standard deviation, and the relation between QT and RR variability expressed as a variability ratio were measured among other QT dynamics.

Results: The reproducibility of all QT dynamics was good. All QT dynamics showed circadian variation when calculated on an hourly basis. The day/night variation in slope could be explained by the differences in heart rate, whereas the day/night variation in intercept was heart rate independent.

Conclusion: The present study shows that reliable automatic QT measurements could be performed, encouraging further evaluation of the clinical value of QT dynamics in risk stratification of cardiac patients.

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Figures

Figure 1
Figure 1
QT/RR relation: An example of the QT/RR relation for the 24‐hour period. The dark gray and light gray area represents RR QT pairs during the awake period, and the medium gray and light gray RR QT pairs during sleep. The light gray area represents RR QT pairs in the overlap between the awake and sleep period (upper panel). The QT/RR relation for the defined day‐period from 9 AM to noon in the same subject (lower left panel). The QT/RR relation for the defined night‐period from 2 AM to 5 AM in the same subject (lower right panel).
Figure 2
Figure 2
Circadian variation: The hourly mean and standard error of mean. RR, mean R‐R interval; QT, mean QT interval; QTc, mean corrected QT interval by Bazett; SDNN, standard variation of all R‐R intervals; SDQT and SDQTc, standard deviation of all QT and QTc intervals, respectively; VR, variability ratio.
Figure 3
Figure 3
Linear regression for the R‐R interval overlap in the same subject. Linear regression performed on beats with R‐R intervals from 700 to 1000 ms at nighttime (dashed line) and daytime (full line). The lines have similar slopes but higher intercept at night.
See this image and copyright information in PMC

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