CT-Based Hypoperfusion Index Differentiate Rate of Infarct Core Progression Post Stroke

Hypoperfusion index was able to estimate the rate of core progression in patients with stroke who had otherwise unclassified progression by reperfusion trial core time criteria.

By using CT-based hypoperfusion index (HI), investigators were able to differentiate rate of infarct core progression among patients with medium vessel occlusion (MVO) and large vessel occlusion (LVO) within 24 hours after their stroke onset. The ability of HI to estimate these rates may have implications for the selection of patients for reperfusion therapy, according to the study authors.

Led by Ali Nomani, MD, neurologist and stroke specialist, University of Alberta, the study pooled data on 106 patients (MVO: n = 26; LVO: n = 80) with acute stroke and CT perfusion, with an additional validation cohort of 110 patients (MVO: n = 42; LVO: n = 68). Based on prior reports and reperfusion trial core time criteria, fast progressors (6.6%, n = 7) were defined as having core greater than 70 mL within 6 hours of onset. Those with less than or equal to 70 mL, mismatched greater than or equal to 15 mL, and with a mismatched-to-core ratio greater than 1.8 within 6-24 hours were defined as slow progressors (27.4%, n = 29). The remaining 66% (n =70) were not classified and did not meet the fast or slow definitions.

Overall, investigators found an HI of 0.5 was able to successfully distinguish patients with fast from slow core progression with 100% sensitivity, 89% specificity, and an area under the curve (AUC) of 0.94 (95% CI, 0.80-0.99). For those with HI less than 0.5, the median core progression was 0.02 mL/min (interquartile range [IQR], 0-0.06) compared with 0.28 mL/min (IQR, 0.11-0.76) for those with HI greater than 0.5 (P <.001).

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Nomani et al concluded that additional research is necessary, and that “given the ability of HI to assess core progression, patients with LVO or MVO and low NIHSS (National Institutes of Health Stroke Scale) may be of interest to assess.” Of note, baseline median NIHSS was higher in patients with fast progression at 21 (IQR, 20-23) compared with those with slow progression at 14 (IQR, 10-18; P = .03).

Between MeVO and LVO stroke groups, baseline patient characteristics were not significantly different between those with HI less than 0.5 compared with those with HI greater than 0.5. In the MeVO group, median core progression for those with HI less than or equal to 0.5 was 0.03 mL min (IQR, 0-0.07) compared with 0.30 mL/min (IQR, 0.06-0.31) for those with HI greater than 0.5 (P <.001).

In comparison, those with LVO with HI greater than 0.5, the median core progression was 0.02 mL/min (IQR, 0-0.06) compared with 0.26 mL/min (IQR, 0.17-0.80) for patients with HI greater than 0.5 (P <.001). For patients with MVO and LVO, that threshold differentiated fast from slow rate of core progression with AUCs of 0.87 (95% CI, 0.82-0.96) and 0.90 (95% CI, 0.66-0.97), respectively.

Among those in the unclassified stroke group, HIs of greater than 0.5 had faster median progression rates of 0.21 mL/min (IQR, 0.06-0.38) compared with 0.03 mL/min (IQR, 0-0.07) in those with HI less than or equal to 0.5 (P <.001). In the MVO (n = 24) and LVO (n = 46) subgroups, those with HI less than or equal to 0.5 had median core progressions of 0.01 mL/min (IQR, 0-0.07) and 0.03 mL/min (IQR, 0-0.07), respectively. For those with HI greater than 0.5, the median core progressions were 0.30 mL/min (IQR, 0.06-0.31) and 0.20 mL/min (IQR, 0.17-0.38), respectively.

To confirm the HI threshold of 0.5, investigators used a secondary independent cohort, which included similar demographics to that of the first. Results from this analysis did not differ much from what was previously observed, with AUCs of 0.84 (95% CI, 0.72-0.97) and 0.84 (95% CI, 0.72-0.97), respectively, in the MVO and LVO stroke groups.

"HI may also have a role to guide decisions of late window thrombolysis and transport," the Nomani et al wrote. “Whether late window patients with stroke and high HI benefit from thrombolysis prior to transport for endovascular therapy evaluation will be of interest to explore. How HI assessment of core progression may contribute to decisions of reperfusion therapy and interfacility transport warrants further study."

Nomani AZ, Tatuene JK, Rempel JL, et al. Association of CT-based hypoperfusion index with ischemic core enlargement in patients with medium and large vessel stroke. Neurology. 2021;97(21): e2079-e2087. doi:10.1212/WNL.0000000000012855