Variability in measurement of internal carotid artery stenosis by arch angiography and duplex ultrasonography - Time for a reappraisal?

Objectives: to determine the inter- and intra-observer variability of ICA stenosis measurement using duplex, ECST and NASCET methods. Design: a retrospective review of arch angiograms and carotid duplex scans in 50 patients. Materials and methods: carotid stenoses were calculated by three independent observers according to NASCET and ECST methods. Variation between observers for NASCET and ECST was determined. For each observer, the variation between NASCET and ECST was determined. The variation between duplex and both NASCET and ECST was determined. Results: inter-observer agreement on the degree of ICA stenosis was clinically and statistically good for NASCET but was poorer for ECST. For each observer, comparison between NASCET and ECST showed 95% limits of agreement of around 50 percentage points. Comparison of duplex with NASCET and ECST showed similar 95% limits of agreement. Conclusions: arch angiography allows reproducible measurement of carotid stenosis by the NASCET method between different observers. For the ECST method, reproducibility is not so good. Variations in results between NASCET and ECST and between angiography and duplex are significant. In view of the similar results of the NASCET and ECST trials, this suggests that degree of stenosis may only be a surrogate marker for outcome following carotid endarterectomy.