What is aChallenging Clot? : ADELPHI Consensus Statement from the CLOTS 7.0 Summit.

Abstract

Predicting achallenging clot when performing mechanical thrombectomy in acute stroke can be difficult. One reason for this difficulty is alack of agreement on how to precisely define these clots. We explored the opinions of stroke thrombectomy and clot research experts regarding challenging clots, defined as difficult to recanalize clots by endovascular approaches, and clot/patient features that may be indicative of such clots. Amodified DELPHI technique was used before and during the CLOTS 7.0 Summit, which included experts in thrombectomy and clot research from different specialties. The first round included open-ended questions and the second and final rounds each consisted of 30closed-ended questions, 29on various clinical and clot features, and 1on number of passes before switching techniques. Consensus was defined as agreement ≥ 50%. Features with consensus and rated ≥ 3out of 4on the certainty scale were included in the definition of achallenging clot. Three DELPHI rounds were performed. Panelists achieved consensus on 16/30 questions, of which 8were rated 3or 4on the certainty scale, namely white-colored clots (mean certainty score3.1), calcified clots under histology(3.7) and imaging(3.7), stiff clots(3.0), sticky/adherent clots(3.1), hard clots(3.1), difficult to pass clots(3.1) and clots that are resistant to pulling(3.0). Most panelists considered switching endovascular treatment (EVT) techniques after 2-3 unsuccessful attempts. This DELPHI consensus identified 8distinct features of achallenging clot. The varying degree of certainty amongst the panelists emphasizes the need for more pragmatic studies to enable accurate apriori identification of such occlusions prior to EVT.