Reproducibility of the systolic time intervals: effect of the temporal range of measurements

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Abstract
The aim of this study was to evaluate the reproducibility of conventionally measured systolic time intervals. To that end, three to eight serial measurements were performed on four different groups of healthy subjects (total number, 49) within dissimilar time periods: 1) within 3 h; 2) within 24 h; 3) within 1 to 2 weeks; and 4) within 14 to 18 months. Judged as the mean coefficients of variation, the variability of the systolic time intervals tended to be smallest in the 3 h measurements and largest in the 24 h measurements. The pooled variances of the serial measurements made within 24 h were in general significantly larger than the respective variances in the measurements made within 3 h. This was due to statistically significant diurnal decreases in left ventricular ejection time and total electromechanic systole in the 24 h study. Otherwise the reproducibility of the method was high. For instance, the mean coefficients of variation for ejection time and total electromechanic systole corrected for heart rate were only 1% and 1.2%, respectively, in serial measurements made at identical diurnal time points within 14 to 18 months. The pooled variances of the measurements made within the shortest and longest temporal ranges were not statistically different. It is concluded that measurement of the systolic time intervals is very applicable to intervention and follow-up studies provided the normal circadian rhythmicity of the phases of systole is adequately taken into account in the design of the study.