Maximum flow velocity waveforms at atrioventricular and outflow tract level were studied cross‐sectionally in 19 human fetuses with conducted and/or blocked supraventricular extrasystoles ranging from 25 to 38 weeks of gestation. At outflow tract level, peak systolic velocity and acceleration time for extrasystolic and post‐extrasystolic beats were compared with those for the immediately preceding normal beat. Regression lines were calculated for peak systolic velocities with filling time. At atrioventricular level, peak‐E wave and peak‐A wave velocities and E/A ratio for the extrasystolic and post‐extrasystolic beats were compared with those for the normal beat. At all levels, time‐averaged velocities were compared with reference charts standardized for gestational age. Peak systolic velocity and acceleration time during the post‐extrasystolic beat were higher than during the normal beat; the Frank‐Starling mechanism, post‐extrasystolic potentiation as well as reduced ventricular afterload may all play a role in this. At all measuring levels, time‐averaged velocity during the extrasystolic beat was strikingly lower than the reference velocities. It is postulated that the increased blood volume and contraction force during the post‐extrasystolic beat cause the valve area to become larger, resulting in a relative decrease in velocities measured by Doppler ultrasound. Copyright

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Ultrasound in Obstetrics and Gynecology
Department of Gynaecology & Obstetrics

van der Mooren, K., Wladimiroff, J., & Stijnen, T. (1992). Fetal atrioventricular and outflow tract flow velocity waveforms during conducted and blocked supraventricular extrasystoles. Ultrasound in Obstetrics and Gynecology, 2(3), 182–189. doi:10.1046/j.1469-0705.1992.02030182.x