Perfusion Mismatch Ratio Predictive in Medium Vessel Occlusion Strokes

For medium vessel occlusion strokes, perfusion mismatch ratio predicted follow-up infarct volume, a multinational trial showed, supporting a role similar to that in large vessel occlusion.

In the 94 isolated M2-segment occlusion patients studied, higher mismatch ratio had a beta score of -0.26 (95% CI -0.37 to -0.14, P<0.001) for smaller follow-up infarct volume. The relationship remained significant on multivariate analysis (beta -0.14, 95% CI -0.27 to -0.02, P=0.026).

However, absolute mismatch volume — hypoperfused volume minus the ischemic core volume — wasn’t predictive (P=0.84), Hamza Adel Salim, MD, of the University of Texas MD Anderson Cancer Center in Houston, reported at the at the American Society of Functional Neuroradiology meeting in Newport Beach, California.

Mismatch ratio — a CT-based calculation of the volume of hypoperfused tissue that is potentially salvageable to the volume of the irrecoverable ischemic core — has largely been studied in large vessel occlusion stroke. Clinical trials have shown strong benefit of both thrombolytics and endovascular thrombectomy among patients with higher mismatch, although low mismatch hasn’t necessarily proven a good rule out for thrombectomy selection.

“The performance of mismatch ratio in this population was consistent with its performance in large vessel occlusion,” Salim told MedPage Today. “Predictive value was consistent with what we expected.”

But unlike in large vessel ischemic strokes, trials have had mixed results on benefit of mechanical thrombectomy in distal medium vessel occlusion, he noted: “So the question that needs to be answered here is which distal medium vessel occlusion patient could benefit from thrombectomy? In this study, we’ve shown that mismatch ratio does represent fall of infarct volume in these patients. So this study should pave the way for future studies that could assess whether the treatment of distal medium vessel occlusion patients who had low mismatch ratio is not that beneficial compared to patients who have high mismatch ratio.”

The study included 94 patients in an international registry with prospectively collected data who had been treated from September 2017 through July 2021 for acute ischemic stroke with isolated M2-segment occlusion. Participants had to have baseline perfusion imaging and follow-up CT or MRI for infarct volume assessment.

Other predictors of greater follow-up infarct volume were higher baseline NIH Stroke Scale score, lower Alberta Stroke Program Early CT Score (ASPECTS), and right-sided occlusion (all P<0.05).

Limitations centered on the retrospective observational design, which made selection bias and residual confounding possible. The small cohort was predominantly treated with thrombectomy, limiting treatment comparisons, and the local perfusion processing and CT/MRI-based infarct measurements varied across centers.

Also, high mismatch ratios are sensitive to small estimated core volumes, the researchers cautioned. They called for prospective external validation to confirm mismatch ratio as a biomarker to triage patients for mechanical thrombectomy.

Salim emphasized that the study did not establish that patient’s treatment should be selected based on mismatch ratios in medium vessel occlusion stroke.

It might be useful in the clinical framework as a complement to imaging-based prognostication, he said. However, pending trials demonstrating utility in treatment selection, “its use should be exclusive to the prognosis to tell patients or their families or the clinicians or the neurologists that in these patients we expect to have higher follow-up infarct volume compared to patients who had high mismatch ratio,” Salim said.