Birjiniuk Joav, Timmins Lucas H, Young Mark, Leshnower Bradley G, Oshinski John N, Ku David N, Veeraswamy Ravi K
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA, 30332-0405, USA.
Emory University School of Medicine, 1648 Pierce Drive NE, Atlanta, GA, 30307, USA.
Cardiovasc Eng Technol. 2017 Sep;8(3):378-389. doi: 10.1007/s13239-017-0312-3. Epub 2017 Jun 12.
Understanding of the hemodynamics of Type B aortic dissection may improve outcomes by informing upon patient selection, device design, and deployment strategies. This project characterized changes to aortic hemodynamics as the result of dissection. We hypothesized that dissection would lead to elevated flow reversal and disrupted pulsatile flow patterns in the aorta that can be detected and quantified by non-invasive magnetic resonance imaging. Flexible, anatomic models of both normal aorta and dissected aorta, with a mobile intimal flap containing entry and exit tears, were perfused with a physiologic pulsatile waveform. Four-dimensional phase contrast magnetic resonance (4D PCMR) imaging was used to measure the hemodynamics. These images were processed to quantify pulsatile fluid velocities, flow rate, and flow reversal. Four-dimensional flow imaging in the dissected aorta revealed pockets of reverse flow and vortices primarily in the false lumen. The dissected aorta exhibited significantly greater flow reversal in the proximal-to-mid dissection as compared to normal (21.1 ± 3.8 vs. 1.98 ± 0.4%, p < 0.001). Pulsatility induced unsteady vortices and a pumping motion of the distal intimal flap corresponding to flow reversal. Summed true and false lumen flow rates in dissected models (4.0 ± 2.0 L/min) equaled normal flow rates (3.8 ± 0.1 L/min, p > 0.05), validated against external flow measurement. Pulsatile aortic hemodynamics in the presence of an anatomic, elastic dissection differed significantly from those of both steady flow through a dissection and pulsatile flow through a normal aorta. New hemodynamic features including flow reversal, large exit tear vortices, and pumping action of the mobile intimal flap, were observed. False lumen flow reversal would possess a time-averaged velocity close to stagnation, which may induce future thrombosis. Focal vortices may identify the location of tears that could be covered with a stent-graft. Future correlation of hemodynamics with outcomes may indicate which patients require earlier intervention.
了解B型主动脉夹层的血流动力学，有助于在患者选择、器械设计和植入策略方面做出决策，从而改善治疗效果。本项目旨在研究主动脉夹层对血流动力学的影响。我们假设，主动脉夹层会导致血流逆转增加，以及主动脉搏动性血流模式紊乱，而这可以通过无创磁共振成像检测和量化。采用生理搏动波形灌注正常主动脉和夹层主动脉的柔性解剖模型，模型中的内膜瓣可移动，包含入口和出口撕裂口。利用四维相位对比磁共振（4D PCMR）成像测量血流动力学。对这些图像进行处理，以量化搏动性流体速度、流量和血流逆转。夹层主动脉的四维血流成像显示，主要在假腔中存在逆流区和涡流。与正常主动脉相比，夹层主动脉在近端至中段夹层处的血流逆转明显更大（21.1±3.8% vs. 1.98±0.4%，p<0.001）。搏动性血流诱导了不稳定的涡流以及与血流逆转相对应的远端内膜瓣的泵吸运动。经外部流量测量验证，夹层模型中真腔和假腔的总流量（4.0±2.0 L/min）与正常流量（3.8±0.1 L/min，p>0.05）相等。存在解剖性弹性夹层时的搏动性主动脉血流动力学与通过夹层的稳定血流以及通过正常主动脉的搏动性血流均有显著差异。观察到了新的血流动力学特征，包括血流逆转、大的出口撕裂涡流和可移动内膜瓣的泵吸作用。假腔血流逆转的时间平均速度接近停滞，这可能会导致未来血栓形成。局灶性涡流可能有助于确定可被覆膜支架覆盖的撕裂口位置。未来血流动力学与治疗效果的相关性研究可能会指明哪些患者需要更早进行干预。
