For years, the central focus for emergency department (ED) physicians responding to a patient with suspected stroke was the golden window—the roughly three-hour period following a stroke where tissue plasminogen activator (tPA) is effective without risking bleeding in the brain. In recent months, research has shown the potential for extending the window and fine-tuning patient selection.
Shifting time frames
On Jan. 31, the American Stroke Association (ASA) released updated guidelines for the treatment of ischemic stroke, and stated certain eligible patients could safely receive tPA to dissolve a clot up to 4.5 hours after symptom onset. The guideline was based on the results of European trials, including the European Cooperative Acute Stroke Study.
The extension doesn’t apply to all patients, however, explains Edward C. Jauch, MD, director of the division of emergency medicine at the Medical University of South Carolina in Charleston. Patients older than 80 years old, those taking oral anticoagulants and those with a National Institutes of Health Stroke Scale score of 25 or higher are not recommended to receive tPA past three hours as its effectiveness in these populations is not well established.
But the golden window—which Jauch says is “probably a misnomer”—is really about treatment selection. Research indicates that imaging, rather than strict adherence to the clock, can provide valuable information for stroke treatment.
|The top row shows a stroke on DWI/ADC which has some enhancement on post-contrast T1 imaging. The bottom row shows the perfusion deficit on a TTP map, the permeability image when not corrected for arrival time and the permeability image after arrival time correction. The green circles show corresponding areas of contrast leakage on the T1 post contrast and ATC permeability images. (DWI = diffusion weighted image, ADC = apparent diffusion coefficient, PWI = perfusion weighted image, TTP = time to peak, ATC = arrival time corrected).|
|Source: PLos One, Dec. 20, 2012.|
MRI vs. CT … or both?
The standard for imaging patients with a suspected stroke is an immediate CT scan. While CT is sensitive to hemorrhages and offers good visualization of bony anatomy, its primary advantages over MRI are purely logistical—CT is widely available, cheaper and offers rapid image acquisition.
However, newly developed advanced techniques may soon expand the benefits of CT. Preliminary results of the START trial, presented at the 2012 Society of NeuroInterventional Surgery annual meeting, showed CT angiography source images (CTA-SI) could help predict which stroke patients will benefit from endovascular therapy. Researchers, led by Don Frei, MD, of Radiology Imaging Associates at Swedish Medical Center in Denver, used the Alberta Stroke Program Early CT Score (ASPECTS), provided by CTA-SI, to inform treatment decisions rather than relying only on the golden window.
“There is robust scientific evidence supporting ASPECTS as a patient selection tool for endovascular stroke therapy,” says Frei. “MRI is a robust patient selector, but any delay in time to recanalization is detrimental to good outcomes. In our practice, [ASPECTS] is fast to acquire and easy to evaluate on the fly in selecting patients for recanalization.”
|2 for 1 stroke imaging driving cost increases|
As techniques in stroke imaging improve for MRI and CT, many providers appear to use both, which could have contributed to a more than 40 percent increase in the cost of stroke care across the U.S. since the late 1990s, according to a study published February 2012 in the Annals of Neurology.
"What we're doing is neither standardized nor efficient," says James F. Burke, MD, of the University of Michigan Medical School in Ann Arbor. Results of the study found that 95 percent of stroke patients who received MRI also had a CT scan.
Burke and colleagues studied patients diagnosed with stroke from 1999 to 2008 in 11 states, which included a total of 624,842 patients. Overall use of MRI rose dramatically, with wide geographic variation.
The costs of inpatient stroke care jumped $3,800 per case between 1997 and 2007, a 42 percent increase, with neuroimaging identified as the largest driver of costs. Burke says diagnostic imaging is on pace to become the most expensive component of stroke care, surpassing room and board.
Not enough work has been done to determine which patients need an MRI and who would be fine with CT alone, says Burke. "Ultimately, we need an intelligent