Greater clinical impact of thrombectomy compared to thrombolysis in first year of Melbourne Mobile Stroke Unit operation

Abstract

Introduction: The role of mobile stroke units (MSU) in earlier provision of thrombolysis (tPA) is well described, but the effect on endovascular thrombectomy (EVT) is less clear. Despite the theoretical advantages of improved triage and prehospital activation of EVT services, only a small effect on hospital arrival to EVT start has so far been described. We aimed to analyze the clinical benefit of EVT and tPA from operation of the Melbourne MSU in the first year. Methods: First ambulance dispatch to reperfusion treatment commencement (DTT) times between MSU patients receiving reperfusion therapy from November 2017-18 were compared to consecutive control cases during MSU operating hours presenting across metropolitan Melbourne for tPA, and direct and metropolitan transfer patients presenting to the Royal Melbourne Hospital for EVT. Median time difference between MSU and controls was regarded as the 50th quantile using quantile regression analysis. Comparative disability avoidance was estimated for EVT and tPA using calculated time savings. Results: In the first calendar year, the MSU operated for 30.5 service (7-day) weeks. Prehospital tPA was administered to 52 patients, with median time differences for dispatch-to-hospital/scene-arrival of -30 minutes (p<0.0001) and arrival-to-tPA of -17 minutes (p=0.001), resulting in overall DTT time saving of 47 minutes compared to controls. In the same timeframe, 26 patients received EVT with median time difference of -51 minutes (p<0.0001) compared to controls. Prehospital notification resulted in median time difference of -17 minutes (p=0.001) for EVT center-arrival to groin puncture. Using published estimates of disability avoidance per minute of time saved for each reperfusion therapy, the clinical impact of the EVT time saving for the 26 MSU patients is equivalent to the clinical impact of 67 tPA patients treated on the MSU. Conclusion: The clinical impact of Melbourne MSU operation on earlier provision of EVT was greater than that of tPA in the first year of operation, reflecting facilitated triage to EVT centers and early prehospital notification. In locales where EVT capability is limited or unevenly distributed such as Melbourne, facilitation of EVT is likely to be a central driver of MSU operation.