CT perfusion mismatch for identifying thrombectomy patients

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Computerised tomography (CT) perfusion mismatch criteria substantially increases the proportion of patients deemed eligible for thrombectomy compared to clinical core mismatch criteria and, despite larger core volumes, similar functional outcomes at 90 days were observed. These results were presented by Edrich Rodrigues (The University of Melbourne, Melbourne, Australia) at the International Stroke Conference (ISC; 24–26 January 2018, Los Angeles, USA)

The study set out to see if CT perfusion (CTP) imaging mismatch (PIM) criteria would be more inclusive than clinical core mismatch (CCM) in selecting patients with acute ischaemic stroke who would benefit from endovascular thrombectomy. They also wanted to see if thrombectomy treated patients who met PIM criteria but not CCM criteria would not have worse functional outcomes than those who met CCM criteria.

They took a cohort of patients treated at the Royal Melbourne Hospital Comprehensive Stroke Centre who had undergone CTP using iSchemaView RAPID s oftware between January 2013 and June 2017. To be included they needed to have intracranial ICA or M1 occlusions, extracranial ICA occlusions for PIM criteria and a premorbid function deemed appropriate for treatment (mRS 0–3). M2 occlusions were not included in the study.

The group began with 970 patients who had anterior circulation infarcts. Of those, 744 had undergone CTP. The patients were then spilt into those presenting within six hours of symptom onset (n=472) and those presenting between six and 24 hours of symptom onset (n=257) and then those that did not meet the inclusion criteria were excluded. This left a cohort of 320 patients, 272 who had presented within six hours of symptom onset and 48 who had presented between six hours and 24 hours of symptom onset.

The patient characteristics were well matched between the two groups although there was a higher number of tandem occlusions in the under six hour group (13% vs. 5%) and a higher number of extra cranial internal carotid artery occlusions in the 6–24 hour group (27% vs. 9%). The average age of the under six hour group was 71 years compared to 69 years in the six to 24 hour group.

In the pre-six hour group 76% of the cohort met DEFUSE 3 criteria but only 47% met those for DAWN+. The McNemar test for discordance between the two groups was significant at p˂0.0001. The majority of the group (81%) would met EXTEND-IA criteria and there was a McNemar score of p˂ 0.0001 between the EXTEND-IA and DAWN+ eligibility.

Of those that underwent CT perfusion imaging more than six hours after last known well but less than 24 hours, 39% would have been eligible for DAWN compared to 66% for DEFUSE 3 (McNemar score of p=0.001). The McNemar score for DAWN vs. EXTEND-IA was p˂ 0.001, with 81% of patients meeting the EXTEND-IA criteria.

The results showed that using perfusion mismatch criteria substantially increased the proportion of patients deemed eligible for thrombectomy compared to clinical-core mismatch criteria. There was a 29% absolute increase in eligible patients when DEFUSE 3 criteria were used, meaning that for every 3.5 patient who was scanned one extra patient was eligible.

The group also looked to see if thrombectomy treated patients who met perfusion imaging mismatch criteria but not clinical core mismatch criteria would not have worse functional outcomes than those with clinical core mismatch criteria.

Fifty one patients were eligible for DEFUSE 3 but not DAWN. Their functional independence at 90 days (mRS 0–2) was 69% (n=35) and their 90-day mortality was 18% (n=9). Of patients that were eligible for DAWN and DEFUSE 3 (n=84) 44% (n=37) had functional independence at 90 days and 90 day mortality was 16% (n=13). The differences between the groups did not meet statistical significance when adjusted for age, NIHSS score and time from onset to perfusion imaging. The results were similar when DAWN was compared to the EXTEND-IA criteria.

“EXTEND-IA thrombectomy patients with DEFUSE 3 or EXTEND-IA (PIM) criteria that did not meet DAWN (CCM) criteria had similar functional outcomes at 90 days when compared to patients that met both criteria, despite the larger core volumes,” said Rodrigues. He continued, “Extrapolation of our predominantly less than six hour data to the extended time window therefore indicates that PIM rather than CCM would lead to the treatment of substantially more patients, without compromising the functional outcomes.”

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