Influence of heart rate on left ventricular isovolumic relaxation time: a Doppler study in healthy newborns

Left ventricular (LV) isovolumic relaxation time (LVIVRT) obtained by Doppler spectral analysis has emerged as a useful tool to assess diastolic function.(1,2) correction for heart rate (HR) is an important advance for clinical application of LVIVRT, initially reported in healthy adult subjects by simultaneous phonocardiogram and echocardiogram.(3) A recent investigation concerning the duration of Doppler-derived LVIVRT in infancy and adolescence has been published, and correction for HR by dividing the absolute values by the square root of cardiac cycle length has been presented.(4) The aim of our study was to use such technique in healthy new-borns to evaluate the influence of resting HR on LVIVRT and to find a regression equation for the prediction of normal values.