Mohammad Anadani, MD
Mechanical thrombectomy (MT) is the standard of care for acute ischemic stroke treatment. The goal of MT is to restore perfusion to the affected area. Hence, its efficiency is evaluated by the degree of reperfusion at the end of the procedure. The Modified Treatment in Cerebral Ischemia (mTICI) score is the most widely used reperfusion score, and it was used in most of the recent intra-arterial treatment landmark trials to assess the efficacy of mechanical thrombectomy. It was also used to compare different thrombectomy techniques, especially contact aspiration and stent retriever techniques. The mTICI score ranges from 0-3, where 0 means no perfusion and 3 means complete perfusion. In the randomized trial settings, mTICI is usually assessed by core laboratories to avoid overestimation. However, this notion of overestimation by local operators has not been supported by research studies.
In this study, Zhang et al. and his colleagues conducted a study using the MR CLEAN registry to compare the operator mTICI with the core lab mTICI. Patients with intracranial internal carotid artery or middle cerebral artery (M, M2, and M3) occlusions were included. mTICI score was determined by local operators of the participating centers and by core lab (consisting of 8 experienced neuropathologists blinded to the clinical characteristics). Of 1628 patients included in the registry, 1300 patients met inclusion criteria and were included in this study.
The mTICI scores were assessed by both operator and core lab in 1182 patients. Successful reperfusion was achieved in 77% of patients according to operator assessment and in 67% according to core lab assessment (difference 10% [95% CI, 6%-14%]; p <0.001) (Figure 1). The overall agreement between the operator and core lab mTICI scores was 56% (95% CI, 54%-59%). The mTICI was overestimated by operators in 33% of patients and underestimated in 10% of patients (Figure 2). Overestimations were more common with distal occlusions (M2, M3) than proximal occlusions (ICA, M1).
Figure 1: Distribution of modified Treatment In Cerebral Ischemia (mTICI) score assessed by operator and core lab.
Figure 2: Disagreement between operator modified Treatment In Cerebral Ischemia (mTICI) and core lab mTICI score.
With respect to the functional outcome, successful reperfusion scored by core lab or local operators predicted functional independence (mRS 0-2) equally well.
In summary, this study demonstrated a significant disagreement between core lab and local operator assessments, which was mostly related to overestimation of mTICI by the local operators.
This study has multiple limitations. The main limitation, which was acknowledged by the authors, is that the mTICI score was assessed by one core lab member with no interrater agreement. In addition, the authors did not use mTICI 2c category in this study; therefore, the authors, in fact, evaluated TICI (Tomsick et al. 2008) and not mTICI score (Almekhlafi et al. 2014). Finally, TICI and mTICI scores were developed for M1 occlusion, and not well validated for more distal occlusions, especially M3 occlusions (Spiotta et al. 2018), which may explain the more noticeable disagreement in mTICI score in distal occlusions.
References:
Tomsick, T., J. Broderick, J. Carrozella, P. Khatri, M. Hill, Y. Palesch, J. Khoury, and I. I. Investigators Interventional Management of Stroke. 2008. ‘Revascularization results in the Interventional Management of Stroke II trial’, AJNR Am J Neuroradiol, 29: 582-7.
Almekhlafi, M. A., S. Mishra, J. A. Desai, V. Nambiar, O. Volny, A. Goel, M. Eesa, A. M. Demchuk, B. K. Menon, and M. Goyal. 2014. ‘Not all “successful” angiographic reperfusion patients are an equal validation of a modified TICI scoring system’, Interv Neuroradiol, 20: 21-7.
Spiotta, Alejandro M, David Fiorella, Adam S Arthur, Donald Frei, Aquilla S Turk, and Joshua A Hirsch. 2018. ‘The semiotics of distal thrombectomy: towards a TICI score for the target vessel’, J Neurointerv Surg: neurintsurg-2018-014353.
