Postmarketing Surveillance of Thrombectomy Using a Tron FX Stent Retriever for Large and Medium Vessel Occlusion

Background/Objectives: The Tron FX is a stent retriever thrombectomy device that underwent a clinical trial in Japan in 2016. Its key feature is the availability of a 2/15 mm model designed for medium-vessel occlusion (MeVO). This study reports the results of postmarketing surveillance (PMS) conducted from 2019 to 2020. Methods: The PMS included data from 240 patients in whom a Tron FX was used during the first pass at 24 Japanese institutions. Occluded vessels involving the M2 and M3 segments of the middle cerebral artery, anterior cerebral artery, and posterior cerebral artery were classified as MeVO. The recanalization rate, first pass effect (FPE) rate, symptomatic intracranial hemorrhage (sICH) rate, and favorable prognosis rate at 90 days were evaluated. Treatment outcomes were also analyzed for cases in which the device was used after the second pass, excluding those with tandem occlusion, atherothrombotic brain infarction (ATBI), or percutaneous transluminal angioplasty (evaluation-appropriate cases), stratified by MeVO and large vessel occlusion (LVO) and according to Tron FX device size. Results: A total of 244 cases were enrolled, of which 218 were evaluation-appropriate. Across all cases, the recanalization rate (modified Thrombolysis in Cerebral Infarction score ≥ 2b) was 70.9%, the FPE rate was 23.4%, the sICH rate was 3.8%, and the proportion of patients with a good prognosis (modified Rankin Scale score 0-2 at 90 days) was 53.1%. Among evaluation-appropriate cases, excluding those with tandem lesions or ATBI, the corresponding rates were 72.9%, 24.8%, 6.9%, and 45.5%, respectively. When analyzed by occluded vessel type, the rates for MeVO were 71.9%, 23.7%, 6.1%, and 45.7%, respectively, while those for LVO were 74.0%, 26.0%, 7.7%, and 45.1%. According to device size, the outcomes for the 2/15 mm Tron FX were 72.9%, 23.5%, 4.7%, and 50.0%, respectively, and those for the 4/20 mm device were 72.9%, 25.6%, 8.3%, and 42.5%. Conclusions: The PMS results for the Tron FX thrombectomy device were excellent, particularly for MeVO and the 2/15 mm model. These findings suggest that the Tron FX may help improve thrombectomy outcomes in MeVO.