Imaging Shows Mixed Results in Patient Selection for Endovascular Stroke Therapy
A scale for measuring imaging-defined ischemic brain injury shows promise as a predictor of endovascular therapy outcomes in patients with acute ischemic stroke. However, the method does not appear to be useful for selecting which patients will benefit most from an endovascular therapy strategy, according to a study published online December 12, 2013, ahead of print in Stroke.
For a predefined substudy of the Interventional Management of Stroke (IMS)-III trial, Michael D. Hill, MD, of the University of Calgary (Calgary, Canada), and colleagues looked at changes on computed tomographic (CT) angiography in 656 patients with acute moderate-to-severe ischemic stroke using the Alberta Stroke Program Early CT Score (ASPECTS). As part of IMS-III, patients were randomized to IV tPA with or without endovascular therapy within 3 hours from symptom onset. Endovascular therapy consisted of a thrombectomy device or catheter-based delivery of tPA.
In the main IMS-III trial, the primary outcome of functional independence, defined as a modified Rankin Scale score ≤ 2, was similar in the endovascular and tPA groups, with no differences in the primary endpoint among those with moderately severe stroke (P = 0.83) or severe stroke (P = 0.06).
ASPECTS is a 10-point quantitative topographic CT scan score. Segmental assessment of the middle cerebral artery (MCA) territory is made and 1 point is removed from the initial score of 10 if there is evidence of infarction in that region.
Patients’ ASPECTS scores were categorized as follows:
- Favorable: 8-10 (n = 378)
- Unfavorable: 0-7 (n = 278)
- Highly Unfavorable: 0-4 (n = 92)
Higher Scores, Better Outcomes
Baseline demographic and clinical characteristics were similar between subjects with favorable vs. unfavorable baseline ASPECTS scores. However, those with the highest scores were almost twice as likely to achieve a favorable outcome at 90 days as those with lower scores (RR 1.8; 99% CI 1.4-2.4).
There was no clear evidence of a treatment-by-ASPECTS interaction. However, the direction of effect for endovascular therapy was toward fewer good outcomes in patients with highly unfavorable ASPECTS scores. In patients with favorable scores, there was a trend toward a greater treatment effect among those treated earlier and those with proven arterial occlusions.
Irrespective of treatment modality, ASPECTS was a strong prognostic variable. A favorable scan conferred a twofold or greater chance of an independent functional outcome, an effect unchanged after multivariable adjustment. There was a larger effect size among both patients treated earlier (onset-to-tPA time ≤ 120 min) and those with proven internal carotid artery or middle cerebral artery occlusions on CT angiography. The probability of achieving recanalization (arterial occlusion lesion, 2-3) of the primary arterial occlusive lesion (RR 1.3; 99% CI 1.0-1.8) or achieving thrombolysis in cerebral ischemia score 2b/3 reperfusion (RR 2.0; 99% CI 1.2-3.2) also was higher in patients with higher ASPECTS scores.
Who Benefits Most?
Dr. Hill and colleagues say their data support ASPECTS as a strong prognostic factor, equivalent in magnitude of effect to the National Institutes of Health Stroke Scale (NIHSS) score. They add that their data complement existing evidence indicating that only patients with favorable ASPECTS scores are likely to benefit from endovascular revascularization therapy.
One possible explanation for the correlation between the score and outcomes is that stroke may influence defensive vascular mechanisms designed to restore blood flow in the brain. “Favorable ASPECTS is associated with good collateral blood flow allowing ischemic brain tissue to survive for longer time periods and enabling intravenous thrombolytics to attack the thrombus from both sides,” the study authors write. “Moreover, higher ASPECTS may be associated with more distal arterial occlusions with smaller sized thrombi when compared with the proximal occlusion of major cerebral arteries.”
Despite this, about one-fifth of patients with highly unfavorable scans achieved a good functional clinical outcome, they note. Dr. Hill and colleagues “attribute this finding to a linear combination of lower age, faster treatment, lower baseline stroke severity, lower baseline serum glucose, higher number of no baseline occlusion cases, and fewer symptomatic intracranial hemorrhage occurrences as principal reasons for good outcome in this group.”
For now, they say, it remains unclear how, and in whom, ASPECTS is best used.
“Until we can treat all patients quickly with 80% to 90% thrombolysis in cerebral ischemia-3 flow, we will not be able to understand the degree to which baseline imaging—using ASPECTS—is a useful method to select patients for combined intravenous thrombolysis immediately followed by endovascular therapy,” they conclude.
Hill MD, Demchuk AM, Goyal M, et al. Alberta stroke program early computed tomography score to select patients for endovascular treatment: Interventional management of stroke (IMS)-III trial. Stroke. 2013;Epub ahead of print.
- Dr. Hill reports serving as a consultant to Covidien EV3.