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