Increased experience associated with shorter procedure times and better reperfusion rates in mechanical thrombectomy

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operator experience thrombectomy
François Zhu (L) and Grégoire Boulouis (R)

Increasing levels of experience in performing mechanical thrombectomies have been associated with shorter procedural duration and better reperfusion rates in a multicentre study—with the study’s researchers noting that a “theoretical ceiling effect” was observed after about 100 procedures.

Writing in the journal Stroke, lead author François Zhu (Department of Diagnostic and Therapeutic Neuroradiology, Nancy Regional University Hospital Center, University of Lorraine, Nancy, France) and colleagues—under the supervision of Grégoire Boulouis (Diagnostic and Interventional Neuroradiology Department of Tours Hospital, Tours, France)—detail the intentions behind their study, which was to evaluate, among trained interventional neuroradiologists, the impact individual experience has on procedural performance metrics in thrombectomies.

In an introductory statement, the authors note that recent international guidelines issued by the American Heart Association (AHA)/American Stroke Association (ASA), and the European Stroke Organisation (ESO)/European Society of Minimally Invasive Neurological Therapy (ESMINT), have recommended a minimum level of personal experience in neurointerventions at high-volume stroke centres before performing endovascular therapy (EVT) in autonomy—but that this minimum level is “unclearly defined”, and that it is currently unknown whether technical efficiency increases after training, along with increasing EVT experience.

As such, they pooled individual EVT procedural data from five centres in the Endovascular Treatment in Ischemic Stroke (ETIS) registry, and two additional high-volume stroke centres, and conducted a retrospective analysis including all patients treated with mechanical thrombectomy for which operator and procedural metrics were recorded. Operator experience was defined for each operator as a continuous variable, cumulating the number of thrombectomy procedures performed since January 2015, and the study’s endpoints included duration of procedure, final angiographic recanalisation, the overall rate of first-pass complete recanalisation, and the rate of severe procedural complication.

Among 4,516 patients treated with EVT between January 2015 and January 2020, a total of 4,012 procedures—performed by 36 operators at seven distinct centres—were included in the analysis. The mean age of these patients was 70 years, and a total of 2,225 (55.5%) received intravenous tissue-type plasminogen activator (IV-tPA) prior to EVT.

Factors associated with shorter EVT duration in univariable analyses, Zhu and colleagues report, were higher operator experience, intravenous thrombolysis before EVT, local (versus general) anaesthesia, and middle cerebral artery (MCA) occlusion location. They note that similar results were found when considering experience as an ordinal variable, with EVT duration decreasing as the operator’s experience category increased, while multivariable analysis showed that higher operator experience as a continuous variable was associated with a “significantly shorter” procedural duration.

“To assess for a potential ceiling effect in the influence of operator experience on mechanical thrombectomy duration, we sequentially excluded previous procedures by steps of 20 units,” Zhu et al add. “Using this method, we observed that prior experience lost its significant association with mechanical thrombectomy duration between 100 procedures (p=0.02) and 120 procedures (p=0.06).”

In the study, increasing operator experience was “significantly associated” with recanalisation success rates as a dichotomous variable, both in univariable analysis and in the multivariable model. The researchers also assessed for a ceiling effect in the association between experience and successful recanalisation by sequentially excluding prior procedures, and found the loss of significance of the association happened between 80 (p=0.03) and 100 procedures (p=0.08).

Notably, they report that there was no effect of operator experience on the overall first-pass complete recanalisation rate after adjusting for general anaesthesia, occlusion location, age and tPA use. Regarding complications, there was no association between operator experience and perforation in either direction—and, similarly, there was no association between operator experience and the rate of reported arterial dissections either.

“Our study […] highlights that, even in trained neurointerventionists operating in autonomy, increasing experience in EVT is associated with better procedural metrics,” Zhu et al write. “The optimal balance between procedural efficiency and safety, and the growing need for thrombectomy-trained interventionists, is still to be found.” The authors conclude that these results may inform future training and practice guidelines to set minimal experience standards before autonomisation, and to set up operators’ recertification processes tailored to individual case volume and prior experience.


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