Stroke scale may incorrectly exclude patients from thrombolysis

November 17, 2005

Excluding stroke patients for thrombolysis based on an established rating of early ischemic changes on CT may not be obligatory, according to a study in the October issue of Stroke.

Excluding stroke patients for thrombolysis based on an established rating of early ischemic changes on CT may not be obligatory, according to a study in the October issue of Stroke.

Researchers from the National Institute of Neurological Disorders and Stroke rtPA Stroke Study Group retrospectively reviewed CT scans to determine whether a semiquantitative scale that scores the extent of early ischemic change within the middle cerebral artery territory could be a treatment modifier.

They found the Alberta Stroke Program Early CT Scale, or ASPECTS, had some benefit but overall did not have a treatment modifying effect on good outcome. They concluded that early treatment appeared to be more critical to thrombolysis and overwhelmed the significance of early CT changes.

The NINDS rtPA Stroke Study was a National Institutes of Health multicenter, prospective, double-blind, placebo-controlled randomized trial of intravenous rtPA for acute ischemic stroke performed from January 1991 through October 1994. It had already demonstrated the efficacy of tPA for acute ischemic stroke within three hours of symptom onset.

CT was used to exclude intracranial hemorrhage before thrombolysis. However, a small proportion of patients developed symptomatic intracranial hemorrhage.

Accumulating evidence suggests that early ischemic change on CT before thrombolysis in acute stroke can predict both functional outcome and the risk of intracranial hemorrhage. But the concept that the risk of intracranial hemorrhage after thrombolysis is related to the degree of early ischemic change has been challenged, according to lead author Dr. Andrew M. Demchuk, director of the Calgary Stroke Programme in Alberta, Canada.

Demchuk and colleagues evaluated 608 baseline CT scans and assessed ASPECTS values by systematically scoring each of 10 regions on the CT scan. They assigned a score of 1 for normal and 0 for a region showing signs of acute ischemia.

Nearly 60% of scans showed early ischemic change with an ASPECTS score of less than 10. There was a trend toward reduced mortality and increased benefit of rtPA at 90 days if the baseline CT scan was favorable (ASPECTS greater than 7). However, these scores did not have a treatment modifying effect on good outcome, and they do not identify patients who should or should not receive thrombolytics.

No mortality reduction was seen in the tPA-treated patients in the ASPECTS 3 to 7 subgroup. Patients with a baseline CT ASPECTS less than 3 had a nonsignificantly higher rate of mortality and symptomatic intracranial hemorrhage with rtPA.

The extent of ischemic change also predicted the likelihood of benefit with a trend to lower number needed to treat. The number needed to treat was 5 when ASPECTS value was greater than 7. When ASPECTS was between 3 and 7, the number needed to treat was 8.

Investigators concluded that their results do not support the concept that quantifying early ischemic change using ASPECTS is critical to intravenous thrombolysis decision making in the first three hours from acute stroke symptom onset.

However, the study revealed that early ischemic change detection was useful to predict the likelihood of benefit. Patients with ASPECTS 8 to 10 had 12% mortality in the rtPA arm and 18% in the placebo arm, suggesting a subgroup of patients with a trend to reduced mortality if rtPA was administered.

The above observation should be tempered, according to researchers, because of the small number of patients enrolled in the trial who had extensive early ischemic changes (3%). In that regard, the study does not provide sufficient evidence to recommend that patients be excluded from rtPA on the basis of extensive early ischemic changes (ASPECTS less than 3).

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