Simple Tool Predicts Target Mismatch in Ischemic Stroke

Nancy A. Melville

March 17, 2017

HOUSTON, Texas — Target mismatch on perfusion imaging in acute ischemic stroke, a key indicator of which patients may still benefit from endovascular intervention, may be predicted with a simple formula of key stroke measures, new research suggests.

The researchers report that the combination of predictors most associated with target mismatch was a computed tomography angiography (CTA)-Alberta Stroke Program Early CT score (ASPECTS) above 4 and National Institutes of Health Stroke Scale (NIHSS) score of less than 16.

"The tool we came up with could be particularly valuable in decision-making at regional stroke care settings of whether to transfer stroke patients from a community hospital that may not have perfusion imaging capability," first author Adam de Havenon, MD, an assistant professor of neurology at the University of Utah School of Medicine, Salt Lake City, told Medscape Medical News.

"The issue is especially important to regional stroke centers because the transfer of a patient can use significant resources, such as sending a helicopter, in addition to taking patients possibly hundreds of miles away from family."

Their findings were presented at the International Stroke Conference (ISC) 2017.

Target mismatch on perfusion MRI or computed tomography (CT) can be critical in indicating the amount of salvageable tissue that is present after stroke, thereby identifying patients who may be best served by interventional therapy, such as intra-arterial tissue plasminogen activator or endovascular thrombectomy.

With perfusion imaging involving advanced technology that is sometimes not available at rural or community centers, however, Dr de Havenon and his colleagues sought to identify other clinical factors and characteristics of CTA, which is more widely available, that were most predictive of target mismatch.

The authors identified 61 patients with acute ischemic stroke who had proximal middle cerebral artery occlusion and were treated at their center from 2010 to 2014 and underwent CTA and CT perfusion imaging upon admission.

Patients had a mean age of 61 years; 61% were male. Their mean NIHSS score was 14.1, and the median follow-up modified Rankin Scale (mRS) score was 3.

Of the patients, 35 (57%) had target mismatch on perfusion imaging, and mRS score was lower among those patients at follow-up (P < .001).

In looking at various factors that community partners would typically be able to provide, and after adjusting for age, medical comorbidities, time from stroke onset, and other factors, the researchers found that the most accurate combination of predictors associated with target mismatch was a CTA-ASPECTS above 4 and NIHSS score of less than 16.

Together, the measures had a sensitivity of 80% and specificity of 85% for target mismatch and a positive predictive value of 88%.

The addition of favorable collateral scores did not improve predictability of target mismatch, Dr de Havenon noted.

"We looked at various possible predictors, and ultimately it ended up being a fairly simple prediction of combining the NIH Stroke Score with an ASPECT score, and together those two were quite predictive of a target mismatch," Dr de Havenon said.

The predictors reflect a general profile of stroke severity, he added.

"I think the combination is kind of a mix between the stroke scale reflecting a moderate severity stroke, but not necessarily severe, and the ASPECT is reflecting a core that is a decent size but not a very large core," he explained.

"So most likely the patients who could be missed with this would be the ones with a very severe stroke in the beginning, but for some reason have a smaller core, and, at least in our analysis, those patients were pretty rare."

"These types of scores are never perfect, but I think this kind of approach to trying to figure out ways to predict who might benefit from a transfer is important due to the hurdles of getting perfusion imaging done at community hospitals," Dr de Havenon said.

The findings are particularly relevant in light of ongoing research in the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution Study (DEFUSE-3) trial  to determine whether patients with target mismatch benefit from endovascular treatment as far out as 6 to 16 hours after they were last seen well, Dr de Havenon noted.

"If we start moving into these longer time windows and routinely do thrombectomies as far out as 12 or 16 hours, it will be useful to have an easily administered but reliable tool to be able to say (for instance), 'Go ahead and put that patient on a helicopter and transfer them as quickly as possible.' "

The authors meanwhile called for further research to replicate the findings.

"This score warrants further study as a tool to guide transfer decisions from primary or secondary stroke centers to tertiary centers where endovascular intervention would be possible for selected patients," they write.

Dr de Havenon has disclosed no relevant financial relationships.

International Stroke Conference (ISC) 2017. Abstract WMP15. Presented February 23, 2017.

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