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Half peak systolic velocity deceleration time: a new index for umbilical artery Doppler, but not a new Doppler parameter for waveform quantification - Reply

Ultrasound in Obstetrics and Gynecology
Wiley Blackwell (John Wiley & Sons)
Publication Date
  • Medicine


Reply Reply We appreciate Dr Carvalho’s interest in our study, which reported normal values for the ‘half peak systolic velocity deceleration time’ in the umbilical artery from 532 normal second- and third-trimester fetuses1. We further used this technique to evaluate placental resistance in seven fetuses with bradycardia, as this Doppler index is independent of the fetal heart rate (FHR). This is not the case for other umbilical artery Doppler indices currently in use, such as the systolic-to-diastolic ratio, resistance index and pulsatility index, which all consider end-diastolic velocities for the calculation and are, therefore, affected by the FHR. We apologize for overlooking Carvalho et al.’s descrip- tion of a similar Doppler technique used in the descending aorta from 17 children with aortic coarctation2. In spite of several methodological and technical differences, includ- ing population, medical condition and targeted vessel studied, we fully agree with Dr Carvalho on the similar- ities between what they called ‘time to half peak systolic velocity’2 and our technique. However, we derived our impedance index from direct measurement of the spectral Doppler waveform and so, unlike Carvalho et al.2, we were unable to correlate our measurement with simul- taneous electrocardiography. We consider that using electrocardiographic landmarks from systole and diastole and correlating them with the arterial Doppler systolic and diastolic velocities is not completely accurate, as there is a delay between the electrical component of the cardiac cycle and the corresponding blood flow velocity waveforms in a distant vessel. In the umbilical artery, this delay may be more pronounced than it is in the descending aorta due to the larger distance from the fetal heart. Although the maximum velocity in a given vessel is the direct result of the ventricular systole, the high- est velocities are actually recorded during early cardiac diastole; therefore, the correct term to use in describ- ing ar

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