Department of Radiology, Leiden University Medical Center.
Department of Cardiology, Leiden University Medical Center, Leiden.
Invest Radiol. 2021 Aug 1;56(8):494-500. doi: 10.1097/RLI.0000000000000768.
Degenerative thoracic aortic aneurysm (TAA) patients are known to be at risk of life-threatening acute aortic events. Guidelines recommend preemptive surgery at diameters of greater than 55 mm, although many patients with small aneurysms show only mild growth rates and more than half of complications occur in aneurysms below this threshold. Thus, assessment of hemodynamics using 4-dimensional flow magnetic resonance has been of interest to obtain more insights in aneurysm development. Nonetheless, the role of aberrant flow patterns in TAA patients is not yet fully understood.
A total of 25 TAA patients and 22 controls underwent time-resolved 3-dimensional phase contrast magnetic resonance imaging with 3-directional velocity encoding (ie, 4-dimensional flow magnetic resonance imaging). Hemodynamic parameters such as vorticity, helicity, and wall shear stress (WSS) were calculated from velocity data in 3 anatomical segments of the ascending aorta (root, proximal, and distal). Regional WSS distribution was assessed for the full cardiac cycle.
Flow vorticity and helicity were significantly lower for TAA patients in all segments. The proximal ascending aorta showed a significant increase in peak WSS in the outer curvature in TAA patients, whereas WSS values at the inner curvature were significantly lower as compared with controls. Furthermore, positive WSS gradients from sinotubular junction to midascending aorta were most prominent in the outer curvature, whereas from midascending aorta to brachiocephalic trunk, the outer curvature showed negative WSS gradients in the TAA group. Controls solely showed a positive gradient at the inner curvature for both segments.
Degenerative TAA patients show a decrease in flow vorticity and helicity, which is likely to cause perturbations in physiological flow patterns. The subsequent differing distribution of WSS might be a contributor to vessel wall remodeling and aneurysm formation.
已知退行性胸主动脉瘤（TAA）患者有发生危及生命的急性主动脉事件的风险。指南建议在直径大于 55 毫米时进行预防性手术，尽管许多小动脉瘤患者的生长速度仅为轻度，并且超过一半的并发症发生在这个阈值以下的动脉瘤中。因此，使用 4 维血流磁共振评估血流动力学已引起人们的兴趣，以获得更多关于动脉瘤发展的见解。尽管如此，TAA 患者异常血流模式的作用尚未完全理解。
共 25 例 TAA 患者和 22 例对照者接受了时间分辨 3 维相位对比磁共振成像和 3 个方向的速度编码（即 4 维血流磁共振成像）。从升主动脉（根部、近端和远端）的 3 个解剖段的速度数据中计算出涡流、螺旋度和壁切应力（WSS）等血流动力学参数。评估了整个心动周期的局部 WSS 分布。
所有节段的 TAA 患者的血流涡流和螺旋度均显著降低。TAA 患者升主动脉近端的外曲度峰值 WSS显著增加，而内曲度的 WSS 值明显低于对照组。此外，从窦管交界处到升主动脉中部的正 WSS 梯度在外曲度最为明显，而在 TAA 组中，从升主动脉中部到头臂干的外曲度出现负 WSS 梯度。对照组在这两个节段的内曲度均仅显示正梯度。
退行性 TAA 患者的血流涡流和螺旋度降低，这可能导致生理血流模式的紊乱。随后 WSS 的不同分布可能是血管壁重塑和动脉瘤形成的原因之一。
