Evaluation of Differences in Automated QT/QTc Measurements between Fukuda Denshi and Nihon Koden Systems
Motoaki SanoYoshiyasu AizawaYoshinori KatsumataNobuhiro NishiyamaSeiji TakatsukiShigeo KamitsujiNaoyuki KamataniKeiichi Fukuda
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Abstract:
Automatic measurement becomes a preference, and indeed a necessity, when analyzing 1000 s of ECGs in the setting of either drug-inducing QT prolongation screening or genome-wide association studies of QT interval. The problem is that individual manufacturers apply different computerized algorithms to measure QT interval. We conducted a comparative study to assess the outcomes with different automated measurements of QT interval between ECG machine manufacturers and validated the related heart rate correction methods.Keywords:
RR interval
The authors hypothesized that the QT-interval depends not only on rate, but also on autonomic influences. To study this, the authors compared QT-intervals within 14 healthy subjects (7 male/7 female, ages 26.0/spl plusmn/3.1 years), at equal heart rates during handgrip and during head-up tilt. QT- and QTc-intervals during handgrip were significantly larger than during tilt (QT: 403/spl plusmn/24 vs. 394/spl plusmn/25 ms; QTc: 436/spl plusmn/16 vs. 426/spl plusmn/15 ms). This finding demonstrates that rate alone is not sufficient to interpret the QT-interval.
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The QT interval from the ECG cannot be measured precisely. The relationship of the QT interval to the RR interval within individuals across time and different RR values, and across individuals eludes complete understanding. Intrinsic beat-to-beat variability in QT interval corrected for heart rate (QTc interval) is not trivial. Therefore, it is difficult to determine a valid and reliable estimate of the time for ventricular repolarization based on the QTc interval. Yet, it must be demonstrated that a drug does not result in an increase in the QTc interval that exceeds 5 ms with some reasonable degree of certainty to be quite confident that the drug does not convey some risk of ventricular tachydysrhythmia due to delayed ventricular repolarization. This demonstration can be a Herculean task due to the magnitude of variability in the QTc interval. Design features and analytical methods that might be used in the thorough QT study to improve the chances of demonstrating the true relationship between a drug and QTc interval are reviewed.
Ventricular Repolarization
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Prolongation
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Background and Objectives
Prolongation of QT interval and QT dispersion (QTD) may be associated with an increased risk of arrhythmias. This study was designed to investigate the effects of right or left stellate ganglion block (SGB) on RR interval, QT interval, the rate-corrected QT (QTc) interval, QTD and the rate-corrected QTD (QTcD) using computerized measurements.Methods
Ten healthy volunteers underwent both right and left SGBs using 7 mL 1% mepivacaine with a 7-day interval between the 2 blocks. The measurement from the 12-lead electrocardiogram was performed for 60 minutes after SGB.Results
Right SGB induced a significant decrease of RR interval immediately after the block, and significant increases of QT interval, QTc interval, QTD, and QTcD from immediately through 50 minutes after the block (P < .01). Left SGB induced a significant decrease of RR interval, and significant increases of QTc interval and QTD immediately after the block (P < .01). Left SGB also produced a significant decrease of QT interval from 20 through 50 minutes after the block, and a significant decrease of QTc interval from 30 through 50 minutes after the block (P < .05).Conclusions
Right SGB induces increases of the QT interval, QTc interval, QTD, and QTcD, and left SGB induces decreases of the QT interval and QTc interval.Prolongation
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The aim of the study was to obtain a set of relevant measurements from healthy, resting horses that can be used as reference values for Holter electrocardiography. Twenty healthy horses (eight mares, two geldings and ten stallions) were selected randomly. The animals varied in age from three to nine years. Electrocardiography was performed at rest in the stable without the presence of the examiner causing additional stress. Each horse was monitored for one hour. P-wave duration, P-wave peak interval, P-R segment, P-R interval, QRS interval, S-T segment, Q-T interval and S-T interval were determined. Median values of the above-mentioned parameters in milliseconds were as follows: 110, 65, 153, 273, 131, 218, 557 and 426, respectively. These values differ significantly from previously published results based on standard electrocardiography.
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