NASHVILLE—The amount of distal flow in the posterior circulation is a robust predictor of subsequent risk of vertebrobasilar stroke, according to data described at the 2015 International Stroke Conference. “Large-vessel flow measurements represent a useful noninvasive method for risk stratification in patients with symptomatic vertebrobasilar disease,” said Sepideh Amin-Hanjani, MD, Codirector of Neurovascular Surgery at the University of Illinois at Chicago.
In contrast with stroke related to carotid disease, few studies have examined risk factors for vertebrobasilar stroke, said Dr. Amin-Hanjani. “Our study used novel MR imaging to assess hemodynamic compromise as a risk factor. No prior studies have measured blood flow in the vertebrobasilar system and examined the effect of reduced distal flow on stroke risk.”
MR Imaging Measured Blood Flow
Dr. Amin-Hanjani and colleagues conducted a prospective observational study called Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke (VERiTAS) to examine the role of hemodynamic compromise in vertebrobasilar disease. They enrolled 73 patients with recent vertebrobasilar transient ischemic attack or stroke at five centers. Eligible participants had at least 50% atherosclerotic stenosis or occlusion in vertebral or basilar arteries.
The investigators measured large-vessel flow in the vertebrobasilar territory using quantitative magnetic resonance angiography, which was enabled by NOVA software. They designated patients as having low flow or normal flow based on regional flow in the distal territory, incorporating collateral capacity. All participants received standard medical management and blinded follow-up assessment. The study’s primary outcome was vertebrobasilar territory stroke.
Stroke Risk Increased With Time
Nearly half (45%) of patients were female, and the population’s mean age was 66 (range, 40 to 90). Two-thirds of participants presented with ischemic stroke. The investigators found that flow status was a significant predictor of subsequent vertebrobasilar stroke. The rates of 12- and 24-month event-free survival were 78% and 71%, respectively, for the low-flow group and 96% and 87%, respectively, for the normal-flow group.
Multivariate analysis with Cox proportional hazards, with adjustment for stroke risk factors, indicated that the hazard ratio for the low-flow group was 18. Medical risk factor management at six-month intervals was similar between low- and normal-flow patients. Flow status remained a significant predictor after adjustment for disease severity and location.
“Interventions such as endovascular angioplasty, stenting, or surgical revascularization procedures can be used to improve blood flow. Our data indicate that the high-risk flow-compromised patients would be the most suitable candidates for such interventions,” said Dr. Amin-Hanjani. “Importantly, our data also indicate that patients with normal flow are at low risk of subsequent stroke on medical therapy and should not receive intervention.”
Further studies are needed to evaluate the risks and benefits of intervention in high-risk patients. “We believe it would be very important to perform additional studies to determine if interventions can safely reduce stroke risk in the high-risk patient population that we have been able to identify based on flow imaging,” Dr. Amin-Hanjani concluded.