Fetal atrioventricular and outflow tract flow velocity waveforms during conducted and blocked supraventricular extrasystoles.
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.
van der Mooren
K
K
Department of Obstetrics and Gynecology, Academic Hospital Rotterdam-Dijkzigt, Erasmus University Rotterdam, Rotterdam, The Netherlands.
Wladimiroff
J W
JW
Stijnen
T
T