Extended thrombolysis window has potential pitfall

By Eleanor McDermid, Senior medwireNews Reporter

The benefits gained from extending the window for thrombolysis in patients with stroke could be lost if the more generous deadline causes physicians to relax, a study suggests.

Researchers looked at data for UK patients included in the Safe Implementation of Treatments in Stroke-International Stroke Thrombolysis Registry and found that if this "deadline effect" approached 45%, equating to about a 20-minute treatment delay, it would cancel out the overall gains derived from extending the thrombolysis window from 3.0 to 4.5 hours.

But Martin Pitt (University of Exeter Medical School, UK) and team stress the benefits of the extended window. "Our study highlights the pitfalls of real-life implementation of research evidence, which cannot be successfully implemented without considering all the factors that may diminish the anticipated benefit," they write in Stroke.

"In so doing, our findings send out a significant warning to those involved with the emergency response for stroke. Patients arriving early in the time window should be treated with the same urgency as if time were imminently running out, and every patient should be treated as quickly as is compatible with safe practice."

The researchers studied 2878 stroke patients who underwent thrombolysis between January 2005 and February 2010 - the period encompassing the publication of the third European Cooperative Acute Stroke Study (ECASS III), which demonstrated benefits for patients treated between 3.0 and 4.5 hours after stroke onset.

Among patients presenting within 90 minutes of symptom onset there was an overall 8-minute, or 20%, reduction in arrival-to-treatment time in the period after versus before ECASS III publication (September 2008). But this did not occur for patients arriving between 90 and 180 minutes after onset, which suggests "a relaxation of treatment urgency associated with the deadline extension," according to Pitt et al.

In a theoretic sample of 1000 stroke patients, the deadline extension would result in an extra 244 patients being treated, but the deadline effect would lead to treatment delays averaging 7.8 minutes in 212 patients.

Even in this scenario, an extra five patients per 1000 would achieve a favorable functional outcome, relative to no deadline extension, but this benefit would be completely lost if the deadline effect caused a 45% delay in treatment. Conversely, the team calculates that a 20% reduction in treatment times across all patients would result in population benefits equivalent to that of the extended thrombolysis window.

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