Adding MRI to CT-based Imaging Reduces Endovascular Stroke Interventions by Half

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The addition of magnetic resonance imaging (MRI) to standard computed tomography (CT) or CT angiography (CTA) screening protocols may allow for better selection of patients with acute large-vessel stroke likely to benefit from endovascular therapy, according to results of a study published online January 9, 2014, ahead of print in Stroke 

Muhammad Shazam Hussain, MD, of the Cleveland Clinic (Cleveland, OH), and colleagues looked at 267 patients presenting with large-vessel occlusion from January 2008 to August 2012. Prior to April 30, 2010, patients were selected for endovascular therapy based on CT/CTA (prehyperacute protocol; n = 88), whereas on or after April 30, 2010, patients were selected based on combined CT/CTA/MRI (hyperacute MRI protocol; n = 179). In the latter protocol, those with a clinically large stroke were taken directly for hyperacute MRI after CTA revealed the presence of a large-vessel occlusion. To minimize time to endovascular therapy, as soon as a clinical examination with baseline (NIHSS ≥ 8) and concomitantly large-vessel occlusion was found on CTA, the endovascular team was activated. Methods and devices used in endovascular interventions were at the discretion of the operator.

Better Outcomes, No Significant Delay

In the hyperacute MRI period, there was a dramatic decline in the percentage of patients who underwent endovascular therapy compared with the pre-MRI period. Much of this difference was attributed to disqualifying patients with large core infarction detected by density-weighted imaging (DWI) that was not seen on noncontrast CT or matched clinical deficits and DWI lesion. Despite the decline in the rate of endovascular therapy, a greater proportion of patients in the hyperacute period had a favorable outcome (based on a modified Rankin scale score of ≤ 2) and decreased mortality at 30 days (table 1).

Table 1. Outcomes at 30 Days

After adjustment for common risk factors, more patients in the MRI period achieved a favorable outcome (adjusted OR 3.6; 95% CI 1.3-10.2; P = 0.014). In addition, MRI-era patients also had a decrease in 30-day mortality (adjusted OR 0.28; 95% CI 0.14-0.5; P < 0.001) compared with pre-MRI patients.

On multiple logistic regression analysis, age, baseline NIHSS score and pretreatment MRI all were significantly associated with favorable clinical outcome at 30 days.

Despite differences in the types of procedures used, recanalization rates were similar between the 2 periods when endovascular therapy was initiated (P = 0.4). However, higher rate of favorable clinical outcome was achieved in the hyperacute MRI period (9.5% vs. 23.9%; P = 0.03) as well as reduced mortality rate (adjusted OR 0.16; 95% CI 0.06-0.37; P < 0.001).

Time, Screening Critical

Importantly, adding pretreatment MRI did not delay time to intervention (468 ± 264 min vs. 483 ± 694 min for pre-MRI period; P = 0.85).

The majority of patients were transferred from other centers with a mean time of arrival of 207 minutes in the pre-MRI period vs. 262 minutes in the MRI period (P=0.04). In longer time windows, the chance of good outcome from unselected populations has been shown to be low, the study authors say, which may make patient selection with imaging that much more important.  

“This presents an opportunity for process improvement to decrease time delays by developing an acute stroke screening and transfer protocols for patients who may be a candidate for [endovascular therapy],” they write.

However, they note that the study did not address the efficacy of endovascular therapy compared with standard medical therapy.

Dr. Hussain and colleagues add that while use of the Alberta Stroke Program Early CT Score (ASPECTS) as a screening tool has been found to be predictive of outcome in a some studies, its low sensitivity in acute stroke makes it unable to “reliably identify those who have substantial volume of irreversibly damaged tissue, and thus patients without a salvageable target will be exposed to therapy.” Although there are few studies of volume in relation to outcome, at least 1 has suggested that patients with DWI core lesions >70 mL are unlikely to achieve good clinical outcome from recanalization.

Importance of Avoiding Harm

In a telephone interview with TCTMD, Philip M. Meyers, MD, of Columbia University Medical Center (New York, NY), said the study sends a critical message by demonstrating the importance of patient selection for endovascular stroke therapy. They clearly show that CT alone may not be adequate to determine which stroke patients should undergo endovascular interventions. The fact that even those who were disqualified by MRI from endovascular procedures had better outcomes is of particular importance, he said.

“If you subject a stroke victim to endovascular therapy when the stroke is already completed, then revascularization may cause more harm than good.  This study suggests that interventions can actually do harm when applied inappropriately or indiscriminately,” he added.

Showing that diagnostic MRI can be performed without creating delays is important too, Dr. Myers noted, because it serves to quell naysayers who argue that such a protocol bogs down a time-sensitive diagnosis and treatment process.

“We need to really start to look at MRI more carefully and to make the operational changes necessary to facilitate access to MRI for patients with acute stroke.  MRI is not commonly seen as an acute care tool, but this study means we need to reconsider that perspective,” Dr. Meyers said.

Finally, he said these data hold an important message for ongoing stroke research. Trials of endovascular stroke therapy must enroll carefully-selected patients who stand a chance to benefit from endovascular revascularization procedures. “We are still learning how to identify appropriate patients,” Dr. Meyers added.

Study Details

Baseline clinical characteristics and stroke severity as measured by median NIHSS score and the retrospectively obtained median ASPECTS score were similar between the groups. There was a higher incidence of A-fib in the pre-MRI than the MRI period (P = 0.02) and fewer extracranial internal carotid artery occlusions (P = 0.03). Additionally, there was a trend toward a lower rate of administration of IV tPA in the pre-MRI vs. MRI period (P = 0.12).

 

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Source:
Wisco D, Uchino K, Saqqur M, et al. Addition of hyperacute MRI aids in patient selection, decreasing the use of endovascular stroke therapy. Stroke. 2014;Epub ahead of print.

 

 

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