Duplex Ultrasound Evaluation of Hemodialysis Access: A Detailed Protocol
Figure 1
(a) The angle of insonation, noted by the phrase “SV Angle” in the upper left hand corner, has been set at 42°. The peak systolic velocity (PSV), the highest point at the top of the waveform, is nearly 80 cm/sec. (b) The same vessel is examined now at an angle of 70°. Marking the highest and lowest points along the waveforms instructs the machine to calculate PSV and the end diastolic velocity (EDV), shown in the lower left hand corner. Using this incorrect angle, the PSV has more than doubled to 175.9 cm/sec. Great care must be taken to avoid this error as PSV is widely used as a diagnostic measure. An improper angle of insonation may thus result in a false impression of stenosis where none actually exists.
