3.2 Core Workflows and Decision Points

3.2 Core Workflows and Decision Points

Each vascular study is a defined sequence of measurements and decisions. The RVT exam tests whether you know the right order, the right control, and the right number at each step.

Carotid duplex workflow

1. Grayscale survey of common (CCA), internal (ICA), external (ECA), and vertebral arteries; characterize plaque (smooth vs irregular, calcified vs soft/heterogeneous).
2. Spectral Doppler with the Doppler angle corrected to <=60 degrees and the cursor parallel to the vessel wall — a sloppy angle inflates velocity and over-grades stenosis.
3. Record PSV, EDV, and the ICA/CCA ratio at the point of maximum velocity.
4. Map the velocities to a stenosis category (SRU consensus criteria below).

Venous duplex (DVT) workflow

The primary test is transverse compression: apply transducer pressure every 1-2 cm down the femoral and popliteal veins. A normal vein walls collapse completely; non-compressibility is the diagnostic finding for acute DVT. Supplement with color fill, distal augmentation (squeeze the calf to provoke flow), and respiratory phasicity. Absent phasicity or augmentation suggests proximal obstruction.

Arterial physiologic workflow

• ABI = highest ankle systolic pressure / highest brachial systolic pressure. Normal 0.91-1.40; claudication 0.41-0.90; rest pain/critical limb ischemia <0.40; >1.40 means calcified noncompressible vessels — switch to toe-brachial index (TBI) (digital arteries resist calcification).
• Segmental pressures: a gradient >20-30 mmHg between adjacent cuffs localizes the diseased level.
• Waveforms: normal arteries are triphasic; disease progresses to biphasic, then monophasic distal to a significant stenosis.

Decision points that trip candidates

When velocities and ratios disagree, weigh PSV most heavily — it has the strongest predictive value for >=70% stenosis. With a contralateral occlusion, ipsilateral velocities are falsely elevated by compensatory flow, so the exam may ask you to down-grade or flag the study rather than report raw numbers.

Vertebral and subclavian workflow

After the carotid, interrogate the vertebral arteries for direction of flow. Antegrade (cephalad) flow is normal. Reversed or alternating (bunny-rabbit) flow points toward subclavian steal from a proximal subclavian or innominate stenosis. Confirm with bilateral brachial blood pressures: a difference greater than 20 mmHg supports a hemodynamically significant subclavian lesion. Provocative arm hyperemia (cuff inflation then release) that deepens the retrograde vertebral flow is the classic confirmatory maneuver tested on the registry.

Spectral analysis details that change the answer

The sample volume should be small (1.5-2 mm) and placed at the center of the stream where velocity is highest; an oversized gate samples slow boundary-layer flow and underestimates the peak. Spectral broadening (filling-in of the spectral window) indicates flow disturbance and post-stenotic turbulence even before the velocity criteria for high-grade stenosis are met. On color Doppler, a focal mosaic or aliasing pattern flags the site of maximum stenosis and tells you where to drop the spectral gate.

Wall filters set too high can erase low diastolic flow and make a patent near-occlusion look occluded, so always lower the filter and the PRF when hunting for the trickle of a string sign.

Tying the workflows together

Each study answers a different clinical question and uses a different primary measurement: carotid duplex uses velocity, venous duplex uses compressibility, and arterial physiologic testing uses pressure and waveform shape. On the exam, the first task in any stem is to identify which study and therefore which primary measurement governs the answer; mixing a venous compressibility concept into an arterial velocity question is one of the most common avoidable errors.

Plethysmography and indirect arterial testing

Beyond duplex, the registry expects familiarity with indirect physiologic arterial methods used when calcification or wounds limit cuff or probe access. Pulse-volume recordings (PVR) measure the volume change in a limb segment with each pulse; a blunted, low-amplitude PVR contour distal to a stenosis localizes disease without needing a measurable pressure, which is valuable in the calcified, noncompressible vessels that defeat the ABI. Photoplethysmography (PPG) at the digit assesses skin perfusion and is the basis of the toe-pressure measurement behind the TBI.

Continuous-wave Doppler at the ankle also yields the waveform shape (triphasic, biphasic, monophasic) used to grade disease when imaging the artery directly is impractical.

Exercise testing and post-exercise ABI

When a patient describes claudication but the resting ABI is borderline or normal, treadmill exercise testing unmasks the disease. A normal artery maintains or only slightly changes the ABI after exercise; a diseased artery shows a marked post-exercise drop in ankle pressure and a delayed recovery time because the fixed stenosis cannot meet the increased demand. A stem describing a normal resting ABI but a sharp post-exercise fall is testing whether you understand that demand-induced ischemia, not the resting number, explains the patient's symptoms.

This mirrors the same continuity-and-demand physiology that governs the velocity criteria throughout the domain.