Elsevier

Journal of Electrocardiology

Volume 41, Issue 6, November–December 2008, Pages 491-497
Journal of Electrocardiology

Subject-specific heart rate dependency of electrocardiographic QT, PQ, and QRS intervals

https://doi.org/10.1016/j.jelectrocard.2008.06.022Get rights and content

Abstract

Although heart rate dependency of QT interval is well known, the relationship of other electrocardiogram (ECG) parameters to heart rate has been researched less intensively. This study investigated the heart rate dependencies of QT interval, PQ interval, and QRS width in 40 healthy subjects (18 women; mean age, 30.4 ± 8.1 years). In each subject, 3 long-term (approximately 13 hours) 12-lead ECGs were obtained for 3 day-time periods with gaps of 2 to 3 weeks between repeated recordings. In each recording, approximately 230 ECG measurements of QT interval, PQ interval, and QRS width were made, each preceded by stable heart rate. For each recording, linear regression slopes of QT/RR, PQ/RR, and QRS/RR relationships were obtained. Intrasubject SDs of individual values were compared with intersubject SDs of intrasubject means to test the individuality of the relationships. The intrasubject means of the slope values were also compared between sexes. The individual SDs of the QT/RR regression slopes were 0.0116 ± 0.0065, whereas the population SD of intrasubject means was 0.0245 (P = 3.6 × 10−15). For the PQ/RR slopes and QRS/RR slopes, these values were 0.0085 ± 0.0050 vs 0.0314 (P = 7.9 × 10−28) and 0.001 89 ± 0.001 57 vs 0.005 50 (P = 2.6 × 10−17), respectively. The QT/RR slopes were steeper in women than in men (0.194 ± 0.019 vs 0.168 ± 0.022, 0.0005), whereas the QRS/RR slopes were, on average, negative in women while positive in men (−0.001 38 ± 0.0045 vs 0.003 35 ± 0.0054, P = .005). There were no sex differences in the PQ/RR slopes (0.054 ± 0.032 in women vs 0.055 ± 0.031 in men, P = .95). Thus, not only the heart rate dependency of QT interval but also the rate dependencies of PQ interval and of QRS width show high intrasubject stability with substantial intersubject differences.

Introduction

Heart rate dependency of the electrocardiographic QT interval has been known for almost a century,1, 2 preceded by much older research on heart rate dependency of mechanical systole.3, 4 The topic of QT/RR relationship has been the subject of numerous studies.5, 6, 7, 8, 9, 10, 11, 12 Data sets of electrocardiograms (ECG) of variable sources, quality, and sizes have been used to investigate the relationship of the QT interval to the heart rate, mostly with the aim of finding a universally valid description of the relationship to convert it into a generally applicable and accurate heart rate correction formula. None of these attempts was truly successful. The reason for this lack of success was found only recently.13 It has been established that although the relationship between the QT interval and the underlying heart rate, or the RR interval representing the underlying heart rate, exhibits substantial intrasubject stability and reproducibility, it also shows fairly high intersubject variability.14, 15 The differences between the QT/RR relationships in different subjects are very large, and consequently, there is no physiologically normal QT/RR pattern in the same way as there is no physiologically normal distribution of the papillary lines of the fingerprint.

Although the heart rate dependency of QT interval has been heavily investigated, the rate relationship of other ECG measurements unrelated to the T wave received much less attention.16, 17 This is likely because the physiologic variability of PQ interval and of QRS complex width is rather small compared with the physiologic variability of (uncorrected) QT intervals. Also, the measurement in classic paper-printed ECG recordings was impossible to make with sufficient precision.

Recent advances in digital electrocardiography and the possibility of obtaining high-quality long-term ECG recordings allow measuring ECG intervals not only with high precision but also systematically without undue influence of the changing ECG morphologies. Using these possibilities, this study investigated the heart rate dependency of PQ intervals and QRS complex durations in a population of young healthy individuals of both sexes. For comparison, the study also researched the QT/RR patterns in the same individuals.

Section snippets

Population

The data of the study originated from the clinical investigation CARISEPY 1025 sponsored by Johnson & Johnson Pharmaceutical Research and Development, Titusville, NJ. The study included repeated long-term 12-lead ECG recordings obtained during day-time hours. For the purposes of this investigation, data were available in 40 healthy subjects, 18 women, mean age, 30.4 ± 8.1 years (range, 19-48 years; interquartile range, 24-36 years). All subjects had normal physical examination at the onset of

Results

Of the 27 600 ECG segments that were initially considered for measurement per study protocol, 27 466 (99.51%) were found preceded by stable heart rate. Of these, QT interval, PQ interval, and QRS width were found measurable in 27 462 (99.99%), 27 372 (99.66%), and 27 454 (99.96%) ECG segments, respectively.

In the total population, the intrasubject averages of the QT/RR, PQ/RR, and QRS/RR regression slopes were 0.180 ± 0.024, 0.00122 ± 0.0055, and 0.0549 ± 0.031, respectively.

The intrasubject

Discussion

The study shows clearly that similar to the high intrasubject stability and large intersubject variability of QT/RR patterns,14, 15 there are equally strong intrasubject stabilities and intersubject variabilities in the PQ/RR and QRS/RR patterns.

The magnitude of the heart rate dependencies that we have observed explains why the QT/RR relationship has been known for a long time, whereas the PQ/RR and QRS/RR relationships are relatively poorly researched. If, in the population of this study,

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    Supported by Johnson & Johnson Pharmaceutical Research and Development by data-provision from the study CARISEPY 1025.

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