But this small pilot study leaves many questions that must be answered before clinical utility can be determined.
The presence of an increased mean blood flow velocity in the middle cerebral artery (MCA) as detected by transcranial Duplex (TCD) sonography following reperfusion in patients with acute ischemic stroke may signal an elevated risk of intracranial hemorrhage, according to a pilot study recently published online ahead of print in the Journal of NeuroInterventional Surgery.
“Intracranial hemorrhage (ICH) is the most serious complication of stroke reperfusion therapies,” senior author Thomas Gattringer, MD (Medical University of Graz, Austria), told Neurovascular Exchange in an email. “There are some established risk factors for ICH in this setting, such as high blood pressure, anticoagulant medications, large infarct size, late treatment, etc.”
Some patients, however, had no known risk factors but “had remarkably increased MCA mean blood flow velocities in the recanalized artery on bedside TCD and then had brain bleeding,” he continued. “This prompted us to systematically study TCD hemodynamics after successful recanalization by mechanical thrombectomy at our stroke center.”
The investigators retrospectively evaluated postinterventional mean blood flow velocities of the recanalized and contralateral MCA, as measured by TCD, in all 123 patients with ischemic stroke who underwent successful endovascular recanalization for anterior circulation vessel occlusion—achieving a TICI score 2b-3—between 2010 and 2017. Mean patient age was 63 years, and 40% were women.
A total of 18 patients had postinterventional ICH, and this group had a higher mean blood flow velocity index in the MCA, defined as the velocity recorded in the recanalized MCA divided by the velocity measured in the contralateral vessel (1.32 vs 1.02; P < 0.001).
Multivariate analysis revealed that a higher velocity index in the MCA was associated with postinterventional ICH (OR 3.6; 95% CI 1.1-3.2) and a poor 90-day outcome, defined as a modified Rankin Scale score of 3 or higher (OR 3.2; 95% CI 1.1-9.7).
Gattringer reported that TCD and measurement of MCA flow velocity are standard and widely available bedside diagnostic tools in neurovascular centers, especially with the advent of portable ultrasound machines. Calculating the MCA flow velocity index, while not standard, would be easy to implement, he said.
“Bedside TCD studies soon after thrombectomy may convey prognostic information and indicate ICH risk,” he said. “At this point we assume that probably closer monitoring and stricter control of blood pressure is indicated in patients with elevated MCA blood flow velocities in the recanalized vessel.”
The findings, Gattringer noted, are “entirely new. … MCA hemodynamics after mechanical thrombectomy and their impact on complications and outcome have not been investigated by TCD so far.” While imaging such as MRI may be the standard in some countries, TCD requires much less expensive technology.
Commenting on the study, David S. Liebeskind, MD (University of California, Los Angeles), told Neurovascular Exchange that, in the United States, advanced diagnostic imaging has largely replaced TCD, relegating it to the role of a “secondary diagnostic procedure.”
He also noted that only patients who remain in the hospital longer than usual would receive follow-up TCD, so the study might have selected sicker patients.
Liebeskind said the study is interesting from a pathophysiological perspective but, at this point, it remains unclear whether it has any clinical utility. He pointed out that Europe, and Austria in particular, has more expertise in the use of TCD than the United States, so it may prove more clinically relevant there. Part of the problem, he said, is that measuring flow velocity alone does not distinguish increases that occur from luminal disease from increases that occur due to vessel narrowing or spasm. It would also be more useful, he said, if serial measures were taken over time.
“The bottom line,” he said, “is does it represent hyperperfusion? Is there increased flow? To make that statement, you have to account for what the vessel is doing. . . . They have patients with hemorrhages at higher velocities, but the causality is not there.”
The study does have some limitations, acknowledged Gattringer. “We do not exactly know how long MCA [mean blood flow] velocity increases preceding a subsequent ICH, as intracerebral bleeding did not lead to clinical deterioration in two-thirds of our patients and was detected only on routine imaging follow-up.” He said the findings should be replicated in a larger multicenter trial, adding that it would be interesting to compare the results with MRI or CT findings.
Source:
Kneihsl M, Niederkorn K, Deutschmann H, et al. Increased middle cerebral artery mean blood flow velocity index after stroke thrombectomy indicates increased risk for intracranial hemorrhage. J NeuroIntervent Surg. 2017;Epub ahead of print.
Disclosure:
Gattringer and Liebeskind report no relevant conflicts of interest.
