Hemodynamics of distal cerebral arteries are associated with functional outcomes in symptomatic ischemic stroke in middle cerebral artery territory: A four-dimensional flow cardiovascular magnetic resonance study.

Background: Cerebrovascular hemodynamics are believed to play an important role in the development of ischemic stroke (IS). However, the relationships between hemodynamics and prognosis are not fully understood. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) enables comprehensive characteristics of cerebrovascular hemodynamics. This study aims to investigate the associations of the different hemodynamics derived from 4D flow CMR with IS functional outcomes.

Methods: Ninety-one patients (median age 64 years, 62 males) with unilateral IS in middle cerebral artery (MCA) territory were included. All subjects underwent a CMR scan, including 4D flow, three-dimensional (3D) time-of-flight magnetic resonance angiography, and 3D whole brain black-blood high-resolution vessel wall imaging of the MCA. Six hemodynamic parameters, including flow rate, velocity, pulsatility index, time-averaged wall shear stress (TAWSS), oscillatory shear index, and relative residence time (RRT), were calculated for the lesion site, pre-bifurcation M1 (pM1) segment, and the distal M1 and/or first branches of M2 (dM1/M2) segments. Vessel characteristics, such as lumen area, vessel area, wall area, maximum wall thickness, and the degree of stenosis, were calculated at the most stenotic lesion site. The modified Rankin Scale (mRS) scores were assessed at 90 days and 1 year, and an mRS >2 was considered as a poor functional outcome.

Results: Lower segment-level TAWSS (odds ratio [OR]: 0.24, P = 0.006 and OR: 0.29, P = 0.014), higher RRT (OR: 2.74, P = 0.007 and OR: 2.40, P = 0.011) of dM1/M2 segments, and lower segment- and lesion-level velocity (OR: 0.40, P = 0.019 and OR: 0.41, P = 0.025; OR: 0.41, P = 0.030 and OR: 0.42, P = 0.040) of pM1 segment were observed to be associated with poor functional outcome at both 90 days and 1 year. Using the cut-off value of 3.58 Pa and 0.29, respectively, TAWSS and RRT of dM1/M2 segments showed moderate performance in distinguishing poor functional outcome from favorable outcome (area under the curve ranging from 0.642-0.687) both at 90 days and 1 year.

Conclusion: Distal segmental TAWSS and RRT of dM1/M2 segments were associated with poor functional outcomes. Such alterations in hemodynamics might help in the identification of patients with potentially unfavorable prognosis.