van Prehn Joffrey, van Herwaarden Joost A, Vincken Koen L, Verhagen Hence J M, Moll Frans L, Bartels Lambertus W
Department of Vascular Surgery, University Medical Center, Utrecht, The Netherlands.
J Vasc Surg. 2009 Jun;49(6):1395-402. doi: 10.1016/j.jvs.2009.02.216.
Electrocardiogram (ECG)-gated imaging offers insight into aortic shape changes throughout the cardiac cycle. Morphologic changes of the anchoring zones may influence stent graft fixation and sealing and may have serious implications for endograft design and durability. We used multiphase magnetic resonance imaging (MRI) scans to evaluate the asymmetric aspect of aortic shape changes in the aneurysm neck before and after endovascular aneurysm repair (EVAR).
Eleven patients were scanned before and after EVAR using ECG-gated balanced gradient-echo MRI with 16 reconstructed phases. Transverse scan planes were planned perpendicular to the aorta in the coronal and sagittal planes. Three levels were studied: 3 cm above the lowest renal artery, between the renal arteries, and 1 cm below the lowest renal artery. After segmentation of the aortic area in the images, aortic radius changes during the cardiac cycle were determined over 360 axes and plotted. Radii were measured from the center of mass of the aortic lumen to the vessel wall. An ellipse was fitted over the plots allowing determination of radius changes over the major and minor axis, and the most prominent direction of distention.
The difference between radius change over the major and minor axis was significant preoperatively and postoperatively (P </= .002) at all levels, indicating asymmetric expansion. The pre-EVAR mean radius change over the major vs minor axis was infrarenal, 0.9 +/- 0.2 vs 0.6 +/- 0.1 mm; juxtarenal, 1.0 +/- 0.2 vs 0.8 +/- 0.1 mm; and suprarenal, 1.3 +/- 0.4 vs 0.9 +/- 0.2 mm. At all levels, there was no significant difference (P > .05) between pre-EVAR and post-EVAR radius changes. Pre-EVAR, the ratio of the radius change over the major vs minor axis ranged from 1.10 to 1.82. The pre-EVAR and post-EVAR asymmetry ratios did not differ significantly (P > .1). Preoperatively, the suprarenal direction of distention showed a tendency to right-anterior; for infrarenal, the tendency was to left-anterior.
We measured the asymmetric aspect of earlier reported pulsatile aortic shape changes. The rate of asymmetric distention varied by patient and level. Asymmetric aortic expansion may have consequences for endograft design because it probably affects endograft sealing, especially in patients with high radius changes and asymmetry ratios. Asymmetric expansion remained preserved after stent graft placement. The stent grafts with Z-stent rings used in the study participants seem to adapt to the aortic shape changes well.
心电图（ECG）门控成像可深入了解整个心动周期中主动脉形态的变化。锚定区的形态变化可能会影响支架移植物的固定和密封，对腔内移植物的设计和耐久性可能产生严重影响。我们使用多期磁共振成像（MRI）扫描来评估血管内动脉瘤修复（EVAR）前后动脉瘤颈部主动脉形态变化的不对称情况。
11例患者在EVAR前后使用ECG门控平衡梯度回波MRI进行扫描，共16个重建期。在冠状面和矢状面中规划垂直于主动脉的横向扫描平面。研究了三个水平：最低肾动脉上方3 cm、肾动脉之间以及最低肾动脉下方1 cm。在图像中分割出主动脉区域后，确定心动周期中主动脉半径在360个轴上的变化并绘图。半径从主动脉腔的质心测量到血管壁。在图上拟合一个椭圆，以确定长轴和短轴上的半径变化以及最明显的扩张方向。
在所有水平上，术前和术后长轴与短轴半径变化的差异均具有统计学意义（P≤0.002），表明存在不对称扩张。EVAR前肾下水平长轴与短轴的平均半径变化分别为0.9±0.2 mm和0.6±0.1 mm；肾周水平为1.0±0.2 mm和0.8±0.1 mm；肾上水平为1.3±0.4 mm和0.9±0.2 mm。在所有水平上，EVAR前和EVAR后半径变化之间均无显著差异（P>0.05）。EVAR前，长轴与短轴半径变化的比值范围为1.10至1.82。EVAR前和EVAR后的不对称比值无显著差异（P>0.1）。术前，肾上扩张方向倾向于右前；肾下倾向于左前。
我们测量了先前报道的搏动性主动脉形态变化的不对称情况。不对称扩张率因患者和水平而异。主动脉不对称扩张可能会对腔内移植物设计产生影响，因为它可能会影响腔内移植物的密封，尤其是在半径变化和不对称比值较高的患者中。支架移植物置入后，不对称扩张仍然存在。本研究参与者使用的带有Z形支架环的支架移植物似乎能很好地适应主动脉形态变化。
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