Tsuyoshi KOGA¹, Shoji SATOH², Yasuyuki FUJITA¹, Hitoo NAKANO¹

¹Department of Obstetrics and Gynecology, Kyushu University Graduate School of Medical Sciences, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan, ²Maternity and Perinatal Care Unit,　Kyushu University Hospital, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan

キーワード : Doppler ultrasound, Fetal cardiac function, Human fetus, Isovolumetric contraction time, Systolic time invervals

The pre-ejection period (PEP) is the most extensively studied electromechanical systolic time interval in the fetus. PEP is the sum of two intervals: the electromechanical interval and isovolumetric contraction time (ICT). PEP is considered to be a sensitive indicator of myocardial performance because ICT, its second component, is directly influenced by myocardial function. Fetal ICT is defined as the interval between the mitral valve closing signal (Mc) and the aortic valve opening signal (Ao) in the suitably filtered cardiac Doppler signal recording. This study attempts to develop a new system for detecting both Mc and Ao using analogue band-pass filters. It also attempts to clarify the usefulness of the fetal ICT measurement. Cardiac Doppler signals obtained from 11 human fetuses between 24 and 37 weeks gestation were recorded using a continuous ultrasound transducer. The raw signal was filtered through 8 types of analogue band-pass filters: 250 to 315, 315 to 400, 400 to 500, 500 to 630, 630 to 800, 800 to 1000, 1000 to 1250 and 1250 to 1500 Hz. These fiItered signals were printed out simultaneously with the raw signal. Investigation showed the 400 to 630 and 800 to 1000 Hz analog filters to be most suitable for detecting Mc and Ao signals, respectively, of the 11 fetuses, and we used them to develop a new Doppler method for measuring fetal ICT. To assess the relationship between PEP and ICT, we simultaneously recorded the fetal scalp electrocardiogram and the fetal Doppler-cardiogram of 2 fetuses during labor, and significant positive linear correlation was noted between PEP and ICT in both cases. We conclude that fetal ICT can be measured simply with suitable band-pass filtering and is useful as a substitute parameter for the pre-ejection period in order to evaluate fetal cardiac function.