Multiparametric Characterization of Tough Clots Following Stroke Thrombectomy

Thrombectomy (TE) is the standard of care for stroke patients with large vessel occlusion. While TE achieves high recanalization rates, a subset of clots requires three or more thrombectomy maneuvers ("challenging or tough clots") which is associated with increased complication rates and poor clinical outcome. The underlying biological properties of tough clots are poorly understood, and it remains unclear whether these have distinct structural characteristics or etiology that might contribute to their resistance to TE.

We performed a prospective, single-center study which analyzed clot composition in 33 consecutive ischemic stroke patients. This included 16 tough clots (48%) which were analyzed in a predefined subgroup analysis. Clots were assessed by preinterventional imaging, ex vivo high field MRI ("MR-microscopy", 9.4 T) and histopathology. Imaging data was correlated with clinical parameters and outcome.

MR microscopy showed mainly platelet-rich clots (white, 21 clots, 64%), whereas mixed (9 clots 27%) and red blood cell-rich (3 clots, 9%) were less frequent. Tough clots were mostly white (14/16 clots, 87.5%), had increased procedure time and required more maneuvers to achieve recanalization (mean number of maneuvers: white clots: 3.2 ± 1.4, mixed clots: 1.7 ± 0.9, RBC-rich clots 1.3 ± 0.6 passes). Cancer patients undergoing thrombectomy and cardiac patients with periprocedural emboli often exhibited tough clots (63% and 67% respectively). TE patients with concomitant cancer had inferior outcome both at discharge and at 90 days follow-up.

Tough clots are platelet-rich, show an association with underlying comorbidities and are associated with malignancies. This highlights the combined influence of clot composition and pre-existing comorbidities on thrombectomy success and supports the need for individualized stroke management.