Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Ga.
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Ga; Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Ga.
J Vasc Surg. 2020 Jun;71(6):2108-2118. doi: 10.1016/j.jvs.2019.06.222.
Endovascular intervention in uncomplicated type B dissection has not been shown conclusively to confer benefit on patients. The hemodynamic effect of primary entry tear coverage is not known. Endovascular stent grafts were deployed in a model of aortic dissection with multiple fenestrations to study these effects. It is hypothesized that endograft deployment will lead to restoration of parabolic true lumen flow as well as elimination of false lumen flow and transluminal jets and vortices locally while maintaining distal false lumen canalization.
Thoracic stent grafts were placed in silicone models of aortic dissection with a compliant and mobile intimal flap and installed in a flow loop. Pulsatile fluid flow was established with a custom positive displacement pump, and the models were imaged by four-dimensional flow magnetic resonance imaging. Full flow fields were acquired in the models, and velocities were extracted to calculate flow rates, reverse flow indices, and oscillatory shear index, the last two of which are measures of stagnant and disturbed flows.
Complete obliteration of the false lumen was achieved in grafted aorta, with normal parabolic flow profiles in the true lumen (maximal velocity, 30.4 ± 8.4 cm/s). A blind false lumen pouch was created distal to this with low-velocity (5.8 ± 2.7 cm/s) and highly reversed (27.9% ± 13.9% reverse flow index) flows. In distal free false lumen segments, flows were comparable to ungrafted conditions with maximal velocities on the order of 7.0 ± 2.1 cm/s. Visualization studies revealed forward flow in these regions with left-handed vortices from true to false lumen. Shear calculations in free false lumen regions demonstrated reduced oscillatory shear index.
Per the initial hypothesis, endovascular grafting improved true lumen hemodynamics in the grafted region. Just distally, a prothrombotic flow regimen was noted in the false lumen, yet free false lumen distal to this remained canalized. Clinically, this suggests a need for advancing endovascular intervention beyond sole entry tear coverage to prevent further false lumen canalization through uncovered fenestrations.
未证实血管内介入治疗单纯型 B 型夹层对患者有益。原发入口撕裂覆盖的血流动力学影响尚不清楚。本研究在主动脉夹层多发破口模型中使用血管内支架移植物来研究这些影响。假设支架移植物的植入将恢复抛物线真腔血流，并消除假腔血流和跨腔射流和涡流，同时保持远端假腔通畅。
将胸主动脉支架移植物放置在具有顺应性和可移动的内膜瓣的硅树脂主动脉夹层模型中，并安装在流循环中。使用定制的正排量泵建立脉动流体流动，通过四维流磁共振成像对模型进行成像。在模型中采集全流场，提取速度以计算流量、反向流量指数和振荡剪切指数，后两者是停滞和紊乱流动的度量。
移植物植入后完全闭塞假腔，真腔出现正常抛物线血流廓线（最大速度为 30.4±8.4cm/s）。在这个假腔的远端形成一个盲袋，具有低流速（5.8±2.7cm/s）和高度反向（27.9%±13.9%反向流量指数）的血流。在远端自由假腔段，血流与未植入的条件相当，最大速度约为 7.0±2.1cm/s。可视化研究显示，这些区域存在从真腔到假腔的顺时针涡流的正向流动。在自由假腔区域的剪切计算显示，振荡剪切指数降低。
根据最初的假设，血管内支架移植物改善了植入区域的真腔血流动力学。仅在远端，假腔出现血栓形成倾向的血流模式，但在这之后的自由假腔仍保持通畅。临床上，这表明需要将血管内干预措施从单纯的入口撕裂覆盖推进到更远端，以防止未覆盖的破口进一步导致假腔通畅。
