Isovolumic relaxation time corrected for heart rate has a constant value from infancy to adolescence.

Isovolumic relaxation time (IVRT) is a valuable adjunct to Doppler flow signals measured at mitral valve level for proper interpretation of left-ventricular diastolic performance. Few data exist on reference values in the pediatric age group. Moreover, routine evaluation of IVRT in patients with limited cooperation ability is impeded by the common technique of simultaneous phono and Doppler shift measurements. To overcome these disadvantages, the IVRT measurements presented are exclusively derived from Doppler shift signals. We set up reference values and investigated the influence of heart rate on that parameter. In 143 healthy participants aged 3 months through 19 years, a complete cardiologic examination was performed in the final evaluation of heart murmurs. We used a Hewlett Packard system 77020AC (Andover, Mass) and 5-, 3.5-, or 2.5-MHz transducers. A total of 63 data sets from a previous study on early and atrial Doppler flow parameters were introduced to this study. IVRT was measured from an apical 4-chamber view, positioning the pulsed wave Doppler sample volume in the left ventricle as much deviated from mitral inflow to left-ventricular outflow so as to visualize, sequentially, both the cessation of aortic outflow and the offspring of mitral flow from the Doppler shift 0 line (Figure 1). Low wall filtering is crucial for this technique. Continuous wave Doppler may be used for IVRT measurements alone, but for inflow measurements continuous wave Doppler is not appropriate. Paper speed was 100 mm/s and the signals were stored on videotape for offline evaluation. Reference values were derived from the mean of measurements in 6 consecutive heart cycles. In addition, we corrected the absolute values of IVRT for heart rate by dividing the absolute value by the square root of cardiac cycle length. Statistical analysis was performed using software (SPSS 9.0, Chicago, Ill). Median values and commercial percentiles for IVRT, and mean and SD for heart rate-corrected IVRT and heart rate were calculated. The influence of heart rate on IVRT was tested by univariate analysis of variance. Informed consent was obtained from the patients or their parents, and the study and local ethics committees approved the study. IVRT has its lowest absolute value during infancy to early childhood and then gradually advances with growth to a level known from investigations in adults (Figure 2). Normalizing the absolute values to cycle length disclosed a powerful inverse correlation between heart rate and IVRT (analysis of variance, R 0.64, P .001), which is in accordance with previous reports. By this correction it was possible to calculate a single reference value of 63 7 milliseconds for all patients in the pediatric age group besides newborns and infants in the second month of life (Figure 3). Measurement reproducibility tested in 20 randomly selected data sets was excellent with R 0.94 for intraobserver variability and R 0.92 for interobserver variability. Both data acquisition exclusively using Doppler shift signals and the ability of working with a single reference value is of major advantage and facilitates substantially the use of IVRT measurements as a routine parameter in echocardiographic examinations in children.