SWIFT PRIME: Who Benefits Most From Thrombectomy in Stroke?

April 19, 2015

GLASGOW, Scotland — New results from the SWIFT PRIME trial show certain groups of patients with acute stroke in whom thrombectomy with a stent retrieval device (Solitaire, Covidien) was particularly effective.

The trial enrolled 196 patients with acute ischemic stroke with confirmed large-vessel anterior circulation occlusions treated with thrombolysis.

The main results of SWIFT PRIME, showing that rapid treatment with the Solitaire device reduced poststroke disability and increased the proportion of patients alive and independent at 3 months, were first presented at the International Stroke Conference in Nashville earlier this year and reported by Medscape Medical News at that time.

The latest subgroup analyses were presented here at the inaugural European Stroke Organisation (ESO) Conference 2015 on April 17 to coincide with the trial's publication online in the New England Journal of Medicine.

Presenting the new subgroup data, Professor Hans-Christoph Diener, MD, from the University Hospital Essen, Germany, reported that the benefit of the intervention was seen across the whole population included, but that certain groups had a particularly large effect.

Among these were patients with the clot in the proximal M1 artery, those with target mismatch (higher ratio of ischemic tissue at risk to irreversibly infarcted brain), patients with longer clots, and those with excellent collateral circulation.

Three other new studies showing benefits of endovascular therapy in patients with stroke were presented at the ESOC 2015 meeting. These were REVASCAT, THERAPY, and THRACE.

Together with SWIFT PRIME and three other previously reported studies (MR CLEAN, ESCAPE, and EXTEND-IA), there are now seven trials showing success with endovascular therapy for acute stroke.

In the SWIFT PRIME publication, the authors, led by Jeffrey Saver, MD, from the University of California, Los Angeles, Stroke Center, point out that the rate of functional independence, defined as a modified Rankin Scale (mRS) score of 0 to 2, in the intervention group in SWIFT PRIME (60%) was higher than that in MR CLEAN (33%) and similar to that observed in the ESCAPE trial (53%) and the EXTEND-IA trial (71%).

They say the better outcome results probably reflect "the earlier start of the intervention, the exclusion of patients with large core infarcts on the basis of imaging, and the greater reperfusion rate in our trial, as compared with the other trials."

In an accompanying editorial, Anthony J. Furlan, MD, from the University Hospitals Case Medical Center, Cleveland, Ohio, suggests that candidates for endovascular therapy should now be directly transported to a comprehensive stroke center as rapidly as possible.

He says transport decisions will be facilitated by the development of algorithms for endovascular therapy. For example, patients with large-vessel occlusions will usually have a baseline National Institute of Health Stroke Scale score of 10 or more, which might become a trigger for transfer to an endovascular center.

Mobile stroke transport units that allow thrombolysis to be started in the field and may also allow computed tomography angiography to screen for large-vessel occlusion are also being evaluated, he notes. Stressing that time is of the essence for endovascular therapy, he says healthcare systems also need to streamline emergency departments and neuroimaging throughput.

Subgroup Analyses

Dr Diener reported that a definite benefit was shown in patients with target mismatch, but there were too few patients with no target mismatch to draw a conclusion.

Table 1. Functional Independence (mRS 0 - 2) at Day 90: Effect of Target Mismatch

Endpoint Intervention + Tissue Plasminogen Activator (tPA) (%) tPA Alone (%) Rate Ratio 95% Confidence Interval (CI)
Target mismatch 62 39 1.61 1.12 to 2.31
No target mismatch 50 33 1.00 0.52 to 4.34

In terms of clot length, there was more benefit in patients with clots longer than 8 mm.

Table 2. Functional Independence (mRS 0 - 2) at Day 90: Effect of Clot Length

Clot Length Intervention + tPA (%) tPA Alone (%) Rate Ratio 95% CI
<8 mm 50 50 1.0 0.32 to 3.10
≥8 mm 71 43 1.67 1.16 to 2.40

There was also a graded effect of the functionality of the collateral circulation, with the best results of thrombectomy seen in patients with excellent collateral flow.

Table 3. Functional independence (mRS 0 - 2) at Day 90: Effect of Collateral Flow

Collateral Circulation Intervention + tPA (%) tPA Alone (%) Rate Ratio 95% CI
None 33 0 NA NA
Good 58 44 1.31 0.78 to 2.19
Excellent 82 28 2.95 1.33 to 6.52

In terms of clot location, Dr Diener said there was benefit across all locations included, but the greatest effect was seen in patients with a clot in the proximal M1 artery. In this group, 88% of patients who underwent thrombectomy achieved functional independence compared with 14% of those given tPA alone.

Dr Diener also reported that higher Alberta Stroke Program Early CT Scores (ASPECTS) were associated with better outcomes in both groups and that thrombectomy was beneficial across the spectrum of ASPECTS included.

Table 4. Functional Independence (mRS 0 - 2) at Day 90: Effect of ASPECTS

ASPECTS Intervention + tPA (%) tPA Alone (%) Rate Ratio 95% CI
6 to 7 42 21 1.98 0.73 to 5.33
8 to 10 66 41 1.62 1.17 to 2.24

In the New England Journal of Medicine article, the authors also report a prespecified analysis comparing the one third of patients who received tPA at an outside hospital and who were transferred for thrombectomy with the two thirds who received both tPA and the endovascular intervention at the study center.

This showed that patients treated with tPA at an outside hospital had less favorable outcomes overall; however, their relative benefit from endovascular therapy did not differ significantly from that observed in patients who received tPA at the study site.

SWIFT PRIME was supported by Covidien. Dr Saver and Dr Diener report receiving personal fees from Covidien during the conduct of the study. Dr Saver is also an employee of the University of California, which holds a patent on retriever devices for stroke.

European Stroke Organisation (ESO) Conference 2015. Abstract 74. Presented April 17, 2015.

N Engl J Med. Published online April 17, 2015. Article full text, Editorial full text


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