Stroke risk prediction in symptomatic anterior circulation ICAD: Analysis of regional QMRA flow from the MYRIAD study

Abstract

Background: Intracranial atherosclerotic disease (ICAD) remains a major source of stroke world-wide, with high recurrence risk. Prior evaluation of posterior circulation ICAD patients enrolled in the prospective VERiTAS and MYRIAD studies revealed regional hypoperfusion assessed by large vessel flow measurements using quantitative MRA (QMRA) predicts subsequent stroke risk. We examined whether a similar approach to regional flow assessment predicted stroke risk in anterior circulation ICAD patients in MYRIAD. Methods: MYRIAD enrolled patients with symptomatic 50-99 % stenosis of proximal intracranial artery. The primary outcome was recurrent ischemic stroke in the stenotic artery territory within one year. Flow was measured in the major intracranial arteries at baseline using QMRA. We designated patients as low or normal flow based on an algorithm assessing distal flow and collateral capacity using age-normalized middle cerebral artery (MCA) and hemispheric flows. Thresholds for flow status categorization were tested to determine the optimal algorithm for stroke risk prediction. Results: Of 73 enrolled subjects with symptomatic anterior circulation ICAD, 7 (9.6 %) had recurrent stroke. Z-score thresholds for age-normalized flow were examined, from which we identified an optimal threshold of -1 for the MCA and -0.75 for hemispheric flow. Based on these thresholds, 24 (33 %) patients were categorized as low flow; recurrent stroke occurred in 21 % of low flow vs 4 % of normal flow patients (age adjusted OR 7.2, 95 % CI 1.2-43.2). In the full cohort of 99 subjects with anterior and posterior circulation ICAD, 11 (11.1 %) had recurrent stroke, with a higher recurrent stroke risk in low flow patients (21.4 % vs 7 %, age adjusted OR 3.8, 95 % CI 1.02-14.2). Conclusions: Distal flow status assessed through QMRA regional flow measurement appears to be similarly predictive for recurrent clinical stroke in both the anterior and posterior ciruclation. Identification of high-risk patients has implications for future investigation of therapeutic interventions.