Balloon guide catheter outcomes by occlusion site in the randomized PROTECT-MT trial

Background Balloon guide catheters (BGCs) are used during endovascular thrombectomy, but whether their effect varies by occlusion site is uncertain. We evaluated effect modification by baseline occlusion site in the PROTECT-MT trial. Methods This exploratory secondary analysis of the randomized PROTECT-MT trial included patients with core laboratory-adjudicated anterior circulation occlusion site data. Patients were classified as having intracranial internal carotid artery (ICA), M1, or M2 occlusion. The primary outcome was the 90-day modified Rankin Scale (mRS) distribution. Treatment effect modification was assessed using adjusted ordinal logistic regression with a treatment-by-occlusion site interaction term. The parent plan prespecified internal carotid artery (ICA) versus middle cerebral artery (MCA) occlusions; the three-level comparison and post hoc Holm correction of 19 secondary interactions were exploratory. Results Among 329 patients, 88 (26.7%) had ICA occlusions, 206 (62.6%) M1 occlusions, and 35 (10.6%) M2 occlusions. The interaction for the 90-day mRS distribution was not statistically significant (P=0.072). Adjusted common ORs with BGC versus control were 0.38 (95% CI 0.17 to 0.85) for ICA occlusions, 0.60 (95% CI 0.36 to 0.99) for M1 occlusions, and 4.32 (95% CI 0.53 to 35.02) for M2 occlusions. No consistent interaction was observed for first-pass or final reperfusion. Secondary interaction analyses remained exploratory after post hoc multiplicity correction. Conclusions This exploratory analysis did not provide conclusive evidence that the occlusion site modified the effect of BGC use on 90-day outcome. Imprecise estimates, particularly for M2, preclude site-specific guide catheter selection. Trial registration number NCT05592054 .