A pulsed wave (PW) Doppler study is an integral part of venous ultrasound. This video explains how to interpret the waveform graph to find out whether a vein contains a clot, where the clot is located and if the patient suffers from venous insufficiency.
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Recall that normal venous waveforms are phasic with respiration, meaning that they approach the baseline with inhalation and go lower below the baseline with exhalation. We saw earlier that distal augments are applied frequently in lower extremity venous studies. Distal augments test patency of the veins proximal to the area you squeeze. A normal distal augment should have an obvious inverted peak below the baseline, meaning there is good blood movement toward the heart with augmentation.
Waveforms proximal to an occlusive deep vein thrombosis, or DVT, are sometimes pulsatile, depending on the amount of phasic superficial venous flow that counteracts the pulsatile area, as well as the patient's cardiac history. Please note that pulsatile waveforms can be seen in patients with right heart failure, but in that case they will occur bilaterally. This is one reason why we always perform a contralateral common femoral vein or CFV Doppler comparison. In patients with right heart failure, a distal augmentation will produce a normal inverted peak below the baseline, indicating no proximal obstruction. If there was a proximal obstruction, an augment would be absent or diminished.
Waveforms within an occlusive DVT will be absent because there is no blood flow and an augment will not produce an augment waveform. We will not perform a distal augment on any leg that has acute DVT due to the risk of the clot embolizing and causing a pulmonary embolus. However, it is important to obtain a PW Doppler waveform distal to the clot to assess for decreased phasicity and confirm the presence of a proximal clot. Distal to a DVT that is either totally or almost totally occlusive, venous waveforms will be continuous.
This means the waveforms will not return to the baseline with inspiration or dip below the baseline with exhalation, but will continue in an unwavering straight line below the baseline. An augment distal to an occlusive DVT will be resistive and show as an absence of any inverted peak or just a small spike below the baseline. Here, you can see continuous venous flow with a resistive augment distal to a significant DVT. The spike above the baseline is normal closure of the valve. Flow proximal to, within and distal to a partially obstructive or recanalized clot can be phasic. This is because there is enough room in the vein lumen around the clot for normal respiratory variation in the waveform.
Distal augmentation can be performed on a chronic clot because of its increased adherence to the vein wall and should also show a normal upside-down peak demonstrating an augment of flow below the baseline. In this image, you can only see a small patch of blue in the vein at the top as there is chronic clot present. The clot is only partially occlusive, though, and so the waveform still shows phasic flow and a normal distal augment. In summary, mormal venous waveforms are phasic, approaching and slowly dipping below the baseline with respiration; proximal to an occlusive DVT, waveforms are sometimes pulsatile; within an occlusive DVT, there will be no waveform obtained because there is no blood flow; and finally, distal to an occlusive DVT, waveforms will be continuous and not change with respiration.