Author + information
- Received December 6, 1990
- Revision received January 10, 1991
- Accepted March 22, 1991
- Published online September 1, 1991.
- ↵∗Address for reprints: Lennart Bergfeldt, MD, PhD, Division of Cardiology, Department of Medicine, Karolinska Institute at Karolinska Hospital, S-104 01 Stockholm, Sweden.
The time-dependent physiologic variations of the cardiac conduction system Here evaluated at repeated invasive studies in 10 healthy individuals. Their mean age was 2S years (range 22 to 34) and they volunteered to undergo two electrophysiologic studies at intervals of 14 to 63 days (mean 25). The coefficients of variation, repeatability and reproducibility, which should be the preferred statistics when assessing the reproducibility of continuous variables, were calculated.
The mean sinus cycle length had a high reproducibility, with coefficients of variation between 2% and 6%. The mean and maximal sinus node recovery times, however, varied considerably. The reproducibility was very high for ventricular depolarization and repolarization (QRS, JT, QT), with coefficients of variation between 2% and 6%. The coefficients of variation were below the acceptable 10% value for intraatrial conduction, atrioventricular (AV) node conduction, His-Purkinje conduction as well as the Wenckebach point; for the effective refractory period of the AV node, it was 12%. Repeat invasive electrophysiologic testing is a safe and reproducible method for evaluating and comparing cardioactive drug effects in healthy subjects.
The same statistical analyses were applied to previously published studies on continuous electrophysiologic variables, which allowed comparisons among different groups of healthy and sick persons, as well as among different electrophysiologic variables and procedures. Furthermore, the minimal actual treatment differences that can be detected with a reasonable (80%) probability at a predetermined (5%) significance level using a crossover design were estimated for different electrophysiologic variables. These data will assist in the calculation of the necessary sample size for clinical trials and related purposes.
☆ This study was supported by grants from the Karolinska Institute, the Swedish Heart-Lung Foundation and the Swedish Society of Cardiology.
☆☆ It was presented in part at the 4th European Symposium on Cardiac Pacing, Stockholm, Sweden, 1989.
- Received December 6, 1990.
- Revision received January 10, 1991.
- Accepted March 22, 1991.