Current practice in ultrasound grading of carotid artery stenosis in the UK and Ireland

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Introduction: Ultrasound is usually the first-line imaging modality in the UK and Ireland for evaluating the severity of carotid artery disease. The last UK and Ireland audit on grading of internal carotid artery (ICA) stenosis with ultrasound was reported in 2006 whilst UK recommendations were published in 2009. This audit aims to summarise current practices. Methods: Seventy-two UK hospital trusts and eight within Ireland that perform carotid surgery were identified. One vascular unit from each trust (n=80) was invited to complete an online questionnaire based on their current carotid ultrasound assessments including velocity thresholds (peak systolic velocity (PSV); end diastolic velocity (EDV)) and PSV ratios (PSV in the ICA:PSV in the common carotid artery (CCA)) used to grade a stenosis, the use of St Mary’s ratio (PSV in the ICA:EDV in the CCA) and the criteria prioritised to grade a stenosis. Results: The questionnaire was answered by 58% (46/80) of vascular units. 70% of respondents reported using the 2009 UK recommendations, with 22% reported using a subset. To grade moderate disease (>50% stenosis), 81% use a PSV of >125 cm.s-1, only 36% use EDV and 71% use a velocity ratio of >2.0–4.0. To grade severe disease (>70% stenosis), 90% use a PSV of >230 cm.s-1, 43% use EDV and 86% use a velocity ratio of >4.0. Whilst the majority (78%) of units use the St Mary’s ratio to grade in deciles, there was more variation in the number of PSV and EDV thresholds used by different centres to grade severe stenosis. There was a combined total of 13 distinct (PSV, EDV and ratios) thresholds being used to grade >80% stenosis. The criteria prioritised to grade a stenosis and how near occlusion was defined on duplex imaging was variable, and there were inconsistent practices on internal audits and quality assurance. Conclusion: The 2009 recommendations have standardised key practices in grading moderate and severe disease with PSV, velocity ratios and in the use of the St Mary’s ratio to grade in deciles. However, vascular units vary in the application of these recommendations and the use of indices not included in the guidelines.

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