Clarifying differences among thrombolysis in cerebral infarction scale variants: is the artery half open or half closed?

Background and Purpose: Although thrombolysis in cerebral infarction (TICI) 2b/3 has been regarded as a successful angiographic outcome, the definition or subclassification of TICI 2 has differed between the original (o-TICI) and modified TICI (m-TICI). We sought to compare interobserver variability for both scores and analyze the subgroups of the TICI 2.
Methods: Five readers interpreted angiographies independently using a 6-point scale as follows: grade 0, no antegrade flow; grade 1, flow past the initial occlusion without tissue reperfusion; grade 2, partial reperfusion in <50% of the affected territory; grade 3, partial reperfusion in 50% to 66%; grade 4, partial reperfusion in ≥ 67%; grade 5, complete perfusion. Readings using this scale were then converted into o-TICI and m-TICI score. Statistical analysis was performed according to TICI 2 subgroups.
Results: Interobserver agreement was good for the o-TICI and m-TICI scores (intraclass correlation coefficient, 0.73 and 0.67, respectively). Our grade 3 (partial perfusion with 50% to 66%) occupied 19% of total readings, which would have been classified as grade 2a in o-TICI, but as 2b in m-TICI. The m-TICI was more likely to predict good clinical outcome than o-TICI (odds ratio, 2.01 versus 1.63, in reads with TICI 2b/3 versus 0/2a).
Conclusions: Both TICI scales showed good agreement among readers. However, the variability in partial perfusion thresholds leads to different grading in ≈ 20% of cases and may result in significantly different rates of accurate outcome prediction.