Association between procedure volume and 30-day mortality in stroke patients treated with EVT or IV rt-PA during the introduction period of EVT in Japan

This study aimed to determine whether procedure volume is associated with 30-day mortality following endovascular thrombectomy (EVT) or intravenous recombinant tissue plasminogen activator (IV rt-PA) for stroke during the introduction period of EVT in Japan. Using nationwide claims records, we investigated data from 8,227 patients undergoing EVT and 13,406 and 6,035 patients undergoing rt-PA monotherapy in hospitals with and without EVT capability, respectively, between April 2014 and February 2016 in Japan. Procedure volume was categorized into three groups according to tertiles of the annual number of EVTs or IV rt-PA injections performed in the hospitals. Hierarchical logistic regression demonstrated that the odds ratio (95% confidence interval) of 30-day mortality following EVT was significantly lower in middle- (0.77 [0.62-0.96]) and high- (0.69 [0.53-0.89]) volume hospitals than that in low-volume hospitals even after adjusting for potential confounding factors. The generalized additive mixed models revealed no obvious threshold volume of EVT to reduce the mortality risk. By contrast, mortality risk following IV rt-PA monotherapy did not decrease in hospitals without EVT capability but did with increasing IV rt-PA volume in hospitals with EVT capability (P for heterogeneity 0.003). The risk of 30-day mortality after EVT for acute ischemic stroke decreased linearly according to EVT procedure volume in each hospital. However, the association between IV rt- PA volume and mortality risk was modified by the hospital's EVT capability. Further research is warranted to determine whether the volume-outcome relationship we observed is a temporary phenomenon following EVT or a consistent trend over time.