What is the clinical evidence from this study?

Study design: Observational. Population: Healthy subjects (n=10). Intervention: 24-hour ambulatory ECG recordings. Primary outcome: Reproducibility of QT parameters (coefficient of repeatability, relative error, and ratio between within-subject and between-subject variability).

January 1, 2001Open Access

Reproducibility of QT Parameters Derived from 24‐hour Ambulatory ECG Recordings in Healthy Subjects

Key Result

QT(60)day derived from 24-hour ambulatory ECG recordings demonstrated high reproducibility with a coefficient of repeatability of 19 ms and a relative error of 1.8%.

Study Design

Type

Observational (n=10)

Structured PICO

Population

10 healthy volunteers aged 25 to 41 years

Intervention

Measurement of QT parameters from two 24-hour ambulatory ECG recordings obtained 1 day apart

Outcome

Reproducibility of QT parameters (coefficient of repeatability, relative error, and ratio between within-subject and between-subject variability)surrogate

QT(60)day derived from 24-hour ambulatory ECG has high reproducibility and may be a suitable alternative to resting ECG QT measurements in clinical trials.

Limitations

Inaccuracy of QT measurement accounted for approximately 40% of the day-to-day variation.
High variation for slope(night) and DeltaQT(60) parameters, which should be used with caution.

Abstract

AIM: To estimate the reproducibility of QT parameters derived from 24-hour ambulatory ECG recordings. METHOD: Ten healthy volunteers aged 25 to 41 years participated. In two 24-hour ambulatory ECG recordings obtained 1 day apart, the QT interval was measured manually at stable heart rates in approximately 16 periods during daytime and 6 periods during nighttime. The association between the QT and RR interval was described by linear regression for day and nighttime separately and the following QT parameters were calculated: the QT interval at heart rate 60 beats/min during daytime (QT(60)day), slope(day), slope(night), and the difference in QT(60) between day and nighttime (DeltaQT(60)). The QT parameters were assessed four times for each participant to discriminate method inaccuracy from day to day variation. The reproducibility was estimated as the coefficient of repeatability, the relative error, and the ratio between within-subject variability and between-subject variability. RESULTS: The coefficient of repeatability, the relative error and the ratio, respectively, were 19 ms, 1.8% and 0.5 for QT(60)day, 0.076, 21% and 0.68 for slope(day), 0.116, 43% and 1.37 for slope(night), and 37 ms, 325% and 1.19 for DeltaQT(60) when estimating the overall day to day reproducibility. Inaccuracy of QT measurement accounted for approximately 40% of this variation, whereas the error caused by selecting segments was small. CONCLUSION: QT(60)day has a high reproducibility and may with advantage replace the conventional QT interval measured on a resting ECG. To assess QT dynamics, the slope of the regression line during daytime is suitable and the short term reproducibility acceptable for clinical trials. Regarding slope(night) and DeltaQT(60), the variation is high and the parameters should be used with caution.