Thrombolysis in Cerebral Infarction Scoring at the Core Lab

Abstract

Core lab adjudication of angiographic reperfusion using the Thrombolysis in Cerebral Infarction (TICI) scale has been an integral component of endovascular stroke therapy trials. 1-7 Despite the specific definitions published on the TICI scoring and its fundamental role as a quality measure in certifying stroke centers, 6 its application at local stroke centers continues to vary. 8 This variability prompted multiple revisions and modifications of the scale. At the same time, the implied equivalence of success in endovascular therapy with more complete reperfusion (i.e., higher TICI scores) prompted some trials to reduce the scale to a dichotomous outcome. For instance, the use of a threshold score of 2B or more in the modified TICI (mTICI) (≥50% reperfusion of the territory downstream of the occlusion) has been widely used to define successful reperfusion after endo-vascular therapy (Table 1). 9 This enforced an inherent bias to overcall TICI scores and subsequently inflated the number of successful procedures. It is not uncommon to see a TICI score of 3 ascribed despite subtle filling defects or delay in contrast opacification on final angiography images. A final TICI score of 3 in these cases ignores the potential interaction between some of these findings with individual patient pathophysiol-ogy and biological factors such as collateral status that may alter the degree and topography of reperfusion. 10 Furthermore, the tendency for overcalling TICI scores widened the gap between the neurological outcomes of patients and the described angiographic success. A recent modification incorporating TICI 2c (also known as the expanded TICI [eTICI]; Fig. 1) have been adopted by the core lab in the Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke Trials (HERMES) collaboration analyses. 11,12 The use of the eTICI is supported by data showing its strong correlation with clinical outcome. 13 The success of endovascular thrombectomy (EVT) procedure centers on achieving fast and complete reperfusion. Angiographic assessment of reperfusion was originally reported using the Thrombolysis in Cerebral Infarction (TICI) scoring published in 2003. Since then, the TICI scoring underwent multiple modifications leading to different interpretations which negatively impacted its reliability. We discuss the implications and nuances of unifying angiographic reporting using the expanded TICI (eTICI) scoring system which was used to report the angio-graphic images of patients enrolled in the Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke Trials collaboration. We propose the use of this eTICI scoring as a reference in core labs of future EVT trials and in clinical practice. We also discuss solutions to help to bridge the gap that currently exists due to the different interpretations of the TICI score. Unified reporting of the an-giographic outcome of EVT procedures is paramount to advancing the field and improving the understanding of predictors of functional outcome especially with the current high rates of successful reperfusion.