A new and simple Doppler method for measurement of fetal cardiac isovolumetric contraction time

Objectives The fetal cardiac isovolumetric contraction time is defined as t he interval between mitral valve closure and aortic valve opening. The obje ctive of this study was to develop a simple and reliable Doppler method for measuring fetal isovolumetric contraction time using a digital filtering a nd processing system. Methods Cardiac Doppler signals were recorded from 40 fetuses at 18-40 week s' gestation using a continuous-wave ultrasound transducer. The raw signal was digitized, filtered and divided into five different frequency ranges: 2 50-375, 375-500, 500-750, 750-1000 and 1000-1500 Hz. To determine the most suitable filter setting for detecting mitral valve closure and aortic valve opening signals, we examined whether they were detected clearly in each fi lter range. Results Both mitral valve closure and aortic valve opening signals were det ected clearly in the 500-1000 Hz range. The a trio ventricular flow and out flow noises in the 250-500 and 1000-1500 Hz ranges helped us to identify th e signals. It was found that dividing the raw signals into three ranges of 250-500, 500-1000 and 1000-1500 Hz was the most suitable digital-filter set ting for measuring isovolumetric contraction time. Conclusions We have developed a simple Doppler method for measuring fetal i sovolumetric contraction time. The advent of digital processing has simplif ied the equipment and the simultaneous multidisplay of three different filt ered signals enables easy and accurate measurement.