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Transferring stroke patients from a referring hospital to a comprehensive stroke center for mechanical thrombectomy may be less a race against time per se than a race to preserve leptomeningeal collateral circulation so that the procedure will still be useful, a new study suggested.

Of 316 consecutive patients presenting with initially favorable computed tomography (CT) profiles (Alberta Stroke Program Early CT Score [ASPECTS] 6 and over) at one of 30 primary stroke centers, to the point that they were no longer eligible for endovascular thrombectomy (under American guidelines) when they reached a thrombectomy-capable center, with the transfer deemed futile upon arrival.

For the study, on multivariable analysis performed by Lee H. Schwamm, MD, of Massachusetts General Hospital in Boston, and colleagues, infarct progression resulting in ASPECTS decay was tied to:

• No or poor leptomeningeal collateral flow on CT angiography at the comprehensive stroke center (88.7% versus 18.9%, adjusted OR 5.14, 95% CI 2.20-12.70)
• Higher NIH Stroke Score (median 19 versus 11, adjusted OR 1.13, 95% CI 1.05-1.22)
• Lower baseline ASPECTS (adjusted OR 0.33, 95% CI 0.21-0.47)

Overall, poor or absent collateral blood flow was recorded for 32.6% of patients arriving at a comprehensive stroke center, according to the study published online in JAMA Neurology.

"In patients with ischemic stroke transferred for thrombectomy, poor collateral blood flow and stroke clinical severity are the main determinants of ASPECTS decay. Our findings suggest that in certain subgroups vascular imaging, including collateral assessment, can play a crucial role in determining the benefits of transfer for thrombectomy," Schwamm's group concluded.

Notably, a longer time interval between CTs did not appear to be associated with ASPECTS decay in unadjusted analysis (3.25 versus 3.17 hours, P=0.76).

"In our analysis of the influence of time in our sample stratified by dichotomized collateral blood vessel status (e.g., no or poor versus moderate or good), we determined that transfer time was mildly associated with ASPECTS decay only in patients with better collateral circulation," the authors wrote. "The size of our sample did not allow for analysis in each subgroup of collateral status."

"Although 'time is brain' is a frequent phrase in acute stroke care, each patient has a different rate of stroke evolution as a result of factors such as adequacy of leptomeningeal collateral blood vessels."

The role of collateral blood vessels as assessed by CT angiography may be a predictor of infarct growth in the setting of transferred patients, the team continued. The findings therefore support the use of CT angiography for selected patients at the acute phase of ischemic stroke in referring hospitals and community hospitals, Schwamm and colleagues said, highlighting the "importance of in patients with no or poor collateral blood flow."

In an accompanying editorial, Bruce Campbell, MBBS, BMedSc, PhD, of Royal Melbourne Hospital in Australia, agreed: "These data contribute to the weight of evidence that, at a minimum, aortic arch to cerebral vertex CT angiography should be performed immediately after the noncontrast CT of the brain at the first hospital that assesses the patient."

Campbell noted that the single-phase CT angiography used for collateral assessment by Schwamm's group is less accurate than multiphase CT angiography or CT perfusion, "potentially leading to unwarranted exclusion of patients from endovascular thrombectomy." A multimodal CT approach including dynamic acquisitions by the primary stroke center, then, is preferable and feasible, he said, citing the experience of small, rural hospitals in Australia.

"These acquisitions are well within the hardware capability of most currently operational CT scanners," Campbell continued. "The medical imaging technologist skill required to perform CT angiography is not excessive (and CT perfusion is even more straightforward if there is automated processing software). Perceived barriers at primary stroke centers are surmountable, and the most efficient approach is to get the complete imaging information at the initial presentation: do it right the first time."

Schwamm and colleagues performed their retrospective analysis in patients with acute ischemic stroke (mean age 70.3, with 43.4% women) from 2010 to 2016.

"Our results derive from simulated situations in which we translated findings at the thrombectomy-capable stroke center to apply them to the referring hospital," the team wrote, acknowledging: "Because the evolution of collateral blood flow is not well known, modifications of collateral blood flow may have occurred during the interval time, thus introducing a systematic bias in our approach."