7.2 Arterial Stenosis & Occlusion Diagnostic Criteria

Combine anatomy, velocity, and waveform evidence

Native extremity arterial duplex grades disease by integrating visible lumen narrowing, focal velocity acceleration, spectral disturbance, and distal hemodynamics. A laboratory must use written validated criteria for the vessel and examination. A native superficial femoral artery, bypass graft, and stent are not interchangeable settings. Published numeric thresholds vary with the population and reference standard; avoid calling one ratio universally definitive.

The continuity relationship is volume flow = cross-sectional area × mean velocity. A narrowing often accelerates flow locally, but volume flow can also fall as disease becomes severe. Bernoulli's model explains conversion between static pressure and kinetic energy, while real vessels also lose energy through viscosity and disturbance. Therefore velocity does not rise indefinitely as a lumen approaches occlusion.

Obtain a defensible velocity ratio

The PSV ratio compares the peak systolic velocity in a lesion with an appropriate adjacent reference, typically a normal proximal segment:

$$V_r = \frac{\text{PSV in stenotic jet}}{\text{PSV in suitable proximal reference}}$$

Use representative samples with consistent angle correction at or below 60 degrees and parallel to the actual jet. Avoid placing the reference within another stenosis, a major caliber transition, or a highly disturbed segment. A ratio can reduce some systemic effects but cannot cancel every consequence of tandem disease, low cardiac output, arrhythmia, or bad acquisition.

A focal doubling of PSV is commonly used as evidence supporting at least 50% narrowing in some native-vessel schemes. Other validated protocols use different cutoffs. Higher ratios, often around four in common teaching schemes, support more severe narrowing when anatomy and other findings agree. These are interpretive frameworks, not a way to derive an exact percentage from any isolated number.

Explicit example criteria for practice

For the following exercise only, assume the laboratory's validated native femoropopliteal criteria classify ratios 2.0 to less than 4.0 as 50–74% stenosis and ratios at least 4.0 as at least 75% stenosis, provided supporting imaging is concordant. A jet PSV of 280 cm/s and reference PSV of 90 cm/s give 280/90 = 3.11. Under the stated scheme, that supports 50–74%, not at least 75%. The exact result depends on the stated scheme, so the question must provide it when a boundary matters.

If the reference PSV is depressed by upstream disease, the ratio may overstate the focal lesion. If no suitable normal reference exists, report that limitation. Document the actual velocities and appearance rather than manufacturing a ratio that looks precise but has no defensible denominator.

Recognize the spatial pattern

A tardus-parvus waveform has a delayed rounded systolic upstroke and reduced amplitude. It supports an upstream hemodynamic problem but is not specific to one lesion or one universal acceleration-time threshold. Compare levels and consider systemic cardiac disease when abnormalities are bilateral. Hyperemia can produce forward diastolic flow without the same delayed upstroke; waveform shape and clinical context matter.

Spectral broadening can be real or artifactual. Reduce excessive gain, narrow an oversized sample gate, check angle, and avoid the wall before attributing window filling to turbulence. A color mosaic can represent aliasing as well as disturbed flow. Raise scale or change acquisition appropriately and sample the region rather than equating every mosaic with severe stenosis.

Occlusion versus undetected slow flow

For suspected occlusion, assess the lumen in several planes and optimize color, power, and spectral Doppler. Lower scale and wall filter appropriately, use gain just below noise, and try an alternative window around calcification. Acute thrombus may be hypoechoic; chronic disease may be more fibrotic or calcified, but grayscale alone cannot assign an exact age.

A high-resistance “thump” proximal to an occlusion and distal collateral reconstitution are supportive. They are not required in every case because branch outflow and collateral pathways change the pattern. No signal behind heavy shadowing is an indeterminate segment until adequate evaluation or additional imaging establishes the anatomy. A PSV ratio is not a meaningful stenosis metric inside a truly occluded lumen.

Trace collateral entry and distal runoff. The deep femoral and genicular pathways may reconstitute an artery beyond a chronic femoropopliteal occlusion. Document lesion length and accessible distal vessels for the interpreting clinician. Endovascular therapy can treat selected occlusions as well as stenoses; occlusion does not automatically require open bypass.

Complete the interpretation

Correlate with ABI/TBI, PVR, symptoms, prior intervention, and the full accessible arterial course. A focal lesion may coexist with inflow and runoff disease. Do not declare the remaining segments normal solely because one local pressure gradient is small or one waveform is preserved. Report lesion location, extent, measurements, collateralization, distal findings, and limitations.

Sudden ischemic symptoms, new neurologic deficit in a limb, or suspected acute graft/native occlusion warrant urgent communication. The examination supplies objective evidence; management depends on the patient's limb viability and clinical assessment, not one threshold detached from the rest of the case.

IAC Vascular Testing criteria and protocol requirements, August 2026 — checked October 18, 2026.