New research indicates the time window for a thrombectomy following a stroke is longer than previously thought, but how soon the surgery occurs still matters.
In some cases, the American Stroke Association is now recommending thrombectomies for as long as 24 hours after onset of stroke. The previous recommendation was no longer than 6 hours.
Vanderbilt University Medical Center was a participating hospital in one of the studies that led to the new recommendations. Results of that study, the DEFUSE 3 trial, were published in The New England Journal of Medicine on Jan. 24. It followed another trial with similar conclusions, the DAWN study, published in The New England Journal of Medicine in November 2017.
The studies identified which patients might benefit beyond six hours by screening them with perfusion imaging — computed tomography-based technology that details what areas of the brain might still be salvageable. A thrombectomy entails threading a catheter with a stent retriever through a main artery and directing it to the brain to remove a clot so blood flow can be restored. The surgical intervention is limited to patients with large vessel occlusions.
“Time-to-treatment still does matter regardless of what perfusion imaging does to select certain patients,” said Michael Froehler, MD, PhD, a neuro-interventionalist and director of VUMC’s Cerebrovascular Service, who served as the site principal investigator for the DEFUSE 3 study.
Systems of care — networks between ambulance services, community hospitals and comprehensive stroke centers — need to be reoptimized and reorganized because of the new thrombectomy recommendations, he said. Froehler is the lead author of another study published in December 2017 in Circulation that indicated inter-hospital transfer before a thrombectomy is associated with delayed treatment and worse outcomes.
“There is nearly a 50 percent reduction in the rate of good outcome for patients who are transferred compared to those who are brought directly to a thrombectomy-capable center,” Froehler said. “So certainly that argues we ought to be doing something better in terms of getting patients to the right center as quickly as possible.”
Thrombectomies and the imaging technology required to determine which patients would benefit beyond six hours are currently provided only at highly advanced stroke centers. And only a subset of patients would qualify.
Both studies (DEFUSE 3, DAWN) showed positive results in terms of a benefit for thrombectomy compared to medical therapy, Froehler said.
“However, they both selected patients based specifically on perfusion imaging. That means selecting only the patients that had a relatively smaller area of completed stroke and a relatively larger area of still salvageable brain.”
The DEFUSE 3 study concluded patients who underwent thrombectomies had less disability and a higher rate of functional independence at three months than standard medical therapy alone. However, the study noted that outcomes for those patients in the extended time window were better than outcomes in prior studies for patients treated within six hours.
“This finding may have been due to the selection of patients in the DEFUSE 3 trial with favorable collateral circulation and slower infarct growth,” the study’s authors wrote.
