Elena Zapata-Arriaza, MD

Kim BM, Baek J-H, Heo JH, Kim DJ, Nam HS, Kim YD. Effect of Cumulative Case Volume on Procedural and Clinical Outcomes in Endovascular Thrombectomy. Stroke. 2019;50:1178–1183.

Stroke thrombectomy is here to stay. We have enough evidence to treat anterior circulation strokes in different scenarios, and this evidence grows to go further, treating patients with worse ASPECTS score, longer evolution or older age. This implies increasingly complex patient management, and their assessment in experienced centers will be fundamental. The available literature suggests a powerful direct correlation between endovascular volume and outcomes, both for individual practitioners and for institutions.

With the aim of testing cumulative case volume (CCV) effect on clinical outcomes in stroke patients who underwent endovascular treatment(EVT), the authors included anterior circulation stroke, with intracranial internal carotid artery, M1 and proximal M2 occlusion from January 2011 to December 2015. Seventeen stroke centers participated in this study. Tandem atherosclerotic or dissecting cervical internal carotid artery occlusion accompanied by intracranial large vessel occlusion (LVO) was included. Multifocal LVO (bilateral anterior or involvement of both anterior and posterior circulations) was excluded. Eligible patients received intravenous tPA. EVT was performed under local anesthesia with or without conscious sedation. Stentriever (SR) or contact aspiration (CA) were used for EVT. Two neuroradiologists independently assessed the images for Alberta Stroke Program Early Computed Tomography Score, and 2 interventional neuroradiologists independently assessed whether recanalization was achieved on the catheter angiograms. The reviewers were blind to the clinical outcome. Recanalization success was defined as modified Thrombolysis In Cerebral Ischemia grade 2b or 3 on the final control angiogram. A good outcome was defined as modified Rankin Scale of 0 to 2 at 3 months.

Regarding EVT-CCV, patients were grouped into 5 based on the consecutive number of previous cases at each hospital. The number of cases that were enrolled from each hospital and then assigned to EVT-CCV group (n) was designed to increase by the function of 10×2(n-1). Thus, EVT-CCV group 1 consisted of the first 10 cases (case No. 1–10) at each hospital; group 2, the next 20 cases (case No. 11–30) at each hospital; group 3, the next 40 cases (case No. 31–70) at each hospital; group 4, the next 80 cases (case No. 71–150) at each hospital; and group 5, all cases that case No. was 151 or greater at each hospital. Therefore, the number of hospitals which contributed to patient enrollment was smaller in the latter than in the former group because EVT case volume of each hospital was different during the study period. Only 1 or 2 neurointerventionists performed EVT at each participating hospital. Therefore, regardless of hospitals where they were treated, the patients in the latter group would be treated by more likely experienced operators than in the former group.

Among 955 patients with fulfilled enrollment criteria, overall recanalization and good outcomes rates were 81.3% and 53.9%, respectively. The median numbers of cases per hospital increased according to the CCV-group. The main results are shown in the Figure, which demonstrates that recanalization and good outcome positively correlated with EVT-CCV group, whereas symptomatic intracranial hemorrhage and mortality are lower in more concentrated CCV-groups. Also, door-to-puncture and puncture-to-recanalization times negatively correlated with EVT-CCV group. Finally, EVT-CCV group was independently associated with recanalization (odds ratio, 1.182; 95% CI, 1.029–1.358) and good outcome (odds ratio, 1.187; 95% CI, 1.053–1.337).

Figure. Main results summary. Data derived from Kim BM, Baek J-H, Heo JH, Kim DJ, Nam HS, Kim YD. Effect of Cumulative Case Volume on Procedural and Clinical Outcomes in Endovascular Thrombectomy. Stroke. 2019;50:1178–1183.

In terms of any technique performance, the greater percentage of procedures realized, the greater possibilities of improvement. Carrying out an endovascular treatment in countless situations allows both the interventionist and the stroke team to face situations of different levels of complexity as long as they are carried out in specialized centers. The learning that involves repetition is associated with the mistakes that are made, which must be learned to obtain excellent results. Possibly, the centers in which a high volume of stroke cases are performed with positive results allow even the least experienced interventionist to learn relatively quickly, improving their performance every time. The results obtained in this study display that the repetition of a habit improves it. Experienced teams tend, therefore, increasingly to improve their times, recanalization rates, functional results and, of course, their safety results (mortality and sICH). This could suggest that endovascular treatment in this type of specialized center could overcome the limitations posed by delays due to transfers from peripheral centers. The results of this study would make us think about the necessary number of thrombectomies that should be performed in each center so that optimal performance is obtained, and if the question about the models drip and ship or mothership are subordinated to the level of specialization and the volume of cases of each center.