ICA PSV for 50–69% and ≥70% Stenosis: SRU/IAC 2024 Criteria

What Changed in 2024

The update to the IAC Standards and Guidelines for Vascular Testing Accreditation states that from 08/15/2024, IAC-accredited vascular laboratories must apply the IAC-modified SRU consensus criteria for interpreting internal carotid artery stenosis. The main practical change concerns the lower velocity threshold for the 50–69% category: instead of 125 cm/s, 180 cm/s is used. The PSV threshold for the ≥70% category, but without near occlusion, remains >230 cm/s.

This is important for daily conclusions: the previous formulation of 50–69% stenosis based solely on a PSV of 125–179 cm/s no longer corresponds to the IAC-modified scheme. In such cases, it is necessary to rely on the visual degree of plaque, the ICA/CCA PSV ratio, EDV, and the clinical context of the laboratory protocol.

Answer to the Main Question: PSV for 50–69% and ≥70%

Complete Table of IAC-Modified Criteria

In the IAC approach, ICA PSV remains the main parameter, but the stenosis class should not be derived from a single number. Visual assessment of the plaque and lumen is mandatory, and the ICA/CCA PSV ratio and EDV are used as additional criteria, especially at borderline velocities or technical limitations.

How to Interpret the 125–179 cm/s Range

The most common practical issue after transitioning to IAC 2024 is a patient with plaque in the bifurcation area and an ICA PSV of 125–179 cm/s. According to the original SRU logic, such a velocity fell into the 50–69% category. According to the IAC-modified scheme, this is insufficient: the velocity criterion for 50–69% starts at 180 cm/s.

If visually the plaque does not cause ≥50% narrowing, the ICA/CCA PSV ratio is <2.0, and the EDV is <40 cm/s, the conclusion should correspond to the <50% category. If morphology and additional parameters contradict the PSV, the protocol should reflect this discrepancy rather than mechanically transferring the old SRU threshold.

Why PSV Is Not the Only Criterion

PSV depends not only on the diameter of the residual lumen. It is influenced by the insonation angle, choice of sample volume, cardiac output, tandem lesions, contralateral occlusion, ICA tortuosity, and post-stenotic hemodynamics. Therefore, the IAC-modified criteria maintain a multimodal interpretation: B-mode and color mapping confirm plaque presence, spectral Doppler quantitatively describes flow acceleration, and the ICA/CCA ratio helps reduce the impact of systemic hemodynamics.

Particular caution should be taken when evaluating tortuous segments: local velocity increase at a bend is not equivalent to atherosclerotic stenosis. In such situations, it is better to describe the technical cause of acceleration in the conclusion and not assign a stenosis percentage without convincing plaque.

Criterion ≥70%: What >230 cm/s Means

For stenosis ≥70%, but without signs of near occlusion, the key ICA PSV threshold in both schemes is >230 cm/s. In the IAC-modified table, this should generally correspond to significant plaque, an ICA/CCA PSV ratio >4.0, and an ICA EDV >100 cm/s. If PSV >230 cm/s, but additional signs do not support significant stenosis, verification of the angle, measurement location, tortuosity presence, and spectrum quality is required.

It is important not to confuse the ≥70% category with near occlusion. In near occlusion, velocities can be high, low, or difficult to register, so one PSV does not classify the lesion. The morphological sign of an almost collapsed distal bed and extremely small residual lumen is more important than a numerical threshold.

What to Write in the Conclusion

The conclusion should be compatible with the laboratory's criteria. After implementing IAC 2024 for accreditation, the category according to IAC-modified SRU criteria should be explicitly stated. Optimal structure: side, plaque location, stenosis category, ICA PSV, ICA/CCA PSV ratio, ICA EDV if necessary, and study limitations.

• Example: Right ICA: atherosclerotic plaque at the origin, stenosis 50–69% according to IAC-modified SRU criteria; PSV 195 cm/s, ICA/CCA ratio 2.3, EDV 48 cm/s.
• Example: Left ICA: plaque without hemodynamically significant stenosis, category <50%; PSV 150 cm/s, ICA/CCA ratio 1.7, EDV 35 cm/s.
• Example: Right ICA: stenosis ≥70%, but without signs of near occlusion; PSV 260 cm/s, ICA/CCA ratio 4.4, EDV 110 cm/s.

Minimum Checklist for the Laboratory

1. Update report templates: the lower threshold for 50–69% according to IAC is 180 cm/s, not 125 cm/s.
2. Separate historical SRU criteria and current IAC-modified criteria in local documents.
3. Do not classify 50–69% based solely on a PSV of 125–179 cm/s without confirming morphology and additional parameters.
4. For ≥70%, use PSV >230 cm/s along with a ratio >4.0 and EDV >100 cm/s as supporting signs.
5. Describe near occlusion separately, as velocities are variable in this condition.

Short Summary

For a physician reading a DUS protocol, the key difference is simple: in the original SRU, 50–69% started at 125 cm/s, in IAC 2024 — at 180 cm/s. The threshold for ≥70% in both schemes is >230 cm/s. After 08/15/2024, laboratories aiming for IAC accreditation should use IAC-modified SRU criteria and avoid automatically elevating the stenosis category at a PSV of 125–179 cm/s.