Arno Teutelink

Use of dynamic computed tomography to evaluate pre- and postoperative aortic changes in AAA patients undergoing endovascular aneurysm repair

Purpose: To utilize dynamic computed tomographic angiography (CTA) on pre- and postoperative endovascular aneurysm repair (EVAR) patients to characterize cardiac-induced aortic motion within the aneurysm neck, an essential EVAR sealing zone. Methods: Electrocardiographically-gated CTA datasets were acquired utilizing a 64-slice Philips Brilliance CT scanner on 15 consecutive pre- and postoperative AAA patients. Axial pulsatility measurements were taken at 2 clinically relevant levels within the aneurysm neck: 2 cm above the highest renal artery and 1 cm below the lowest renal artery. Changes in aortic area and diameter were determined. Results: Significant aortic pulsatility exists within the aneurysm neck during the cardiac cycle. Preoperative aortic area increased significantly, with a maximum increase of up to 12.5%. The presence of an endograft did not affect aortic pulsatility (p = NS). Postoperative area also changed significantly during a heart cycle, with a maximum increase of up to 14.5%. Diameter measurements demonstrated an identical pattern, with significant pre- and postoperative intracardiac pulsatility within and above the aneurysm neck (p<0.05). An increase in maximum diameter change up to 15% was evident. Conclusion: Patients undergoing EVAR experience aortic diameter changes within and above the aneurysm neck. The presence of an endograft does not abrogate this response to intracardiac pressure changes. Static CT imaging may not adequately identify patients with large aortic pulsatility, potentially resulting in endograft undersizing, stent-graft migration, intermittent type I endoleaks, and poor patient outcomes. The current standard regime of 10% to 15% oversizing based on static CT may be inadequate for some patients.

Aortic Compliance following EVAR and the Influence of Different Endografts: Determination Using Dynamic MRA

Purpose: To utilize dynamic magnetic resonance angiography (MRA) to characterize aortic stiffness (β) and elastic modulus (Ep) as indexes of wall compliance during the cardiac cycle and determine any influence of different endograft designs or the presence of endoleaks on these indexes. Methods: Eleven consecutive patients (11 men; median age 74 years, range 63–78) with abdominal aortic aneurysm (AAA) selected for endovascular repair were scanned pre- and postoperatively. Aortic area and diameter changes during the cardiac cycle were determined using dynamic MRA at 4 levels: 3 cm above the renal arteries, between the renal arteries, 1 cm below the renal arteries, and at the level of maximum aneurysm sac diameter. Ep and β were calculated. Data are presented as median (range); p<0.05 was considered significant. Results: Preoperatively, Ep and β were significantly higher at the level of the aneurysm sac compared to all other levels (p<0.05). Following EVAR, stiffness increased at this level (p<0.05). After implantation, patients with an Excluder endograft demonstrated Ep and β measurements at the aneurysm neck that were 94% and 60% higher, respectively, compared to those with a Talent (p<0.05) endograft. The presence of an endoleak had no effect on Ep or β. Conclusion: This study introduces the feasibility of dynamic MRA imaging—based calculations of aortic elastic modulus and stiffness. AAA patients demonstrate increased Ep and β at the level of the aneurysm sac. EVAR results in increased aneurysm sac Ep and β. Stent-graft design seems to alter Ep and β within the aneurysm neck, which may have consequences for endograft durability. The presence of an endoleak does not seem to have an effect on Ep or β.

Fabric tears as a new cause of type III endoleak with ancure endograft

PURPOSE We present two case reports of type IIIb endoleak. One was due to fabric erosion caused by placement of a stent (Wallstent; W. L. Gore & Associates, Flagstaff, Ariz) after endovascular aneurysm repair; the other arose spontaneously. In both cases, an Ancure endograft (Guidant/EVT, Menlo Park, Calif) was placed. CASE REPORTS In case 1, a large endoleak developed 36 months after uncomplicated endovascular treatment of an abdominal aortic aneurysm. In case 2, endoleak developed 30 months after a complicated procedure. In both cases, two Wallstents were used to treat type I endoleak and limb kinking in the first postoperative months. One type III endoleak was within the endograft at the level of the stents. CONCLUSION To our knowledge, these are the first type III endoleaks reported in association with Ancure endografts. Placement of Wallstents inside endografts is of concern, and another indication for close monitoring during follow-up.

Pilot study of dynamic cine CT angiography for the evaluation of abdominal aortic aneurysms: Implications for endograft treatment

Purpose: To utilize 40-slice electrocardiographically (ECG)-gated cine computed tomographic angiography (CTA) to characterize normal aortic motion during the cardiac cycle at relevant anatomical landmarks in preoperative abdominal aortic aneurysm (AAA) patients. Methods: In 10 consecutive preoperative AAA patients (10 men; mean age 78.8 years, range 69–86), an ECG-gated CTA dataset was acquired on a 40-slice CT scanner using a standard radiation dose. CTA quality was graded and scan time was measured. Pulsatility measurements at multiple relevant anatomical levels were performed in the axial plane. Changes in aortic circumference were determined for both the aortic wall and the luminal diameter. Results: All 10 CT scans were of good quality. All patients could be scanned in 14 to 33 seconds (mean 21). At each anatomical level measured, there was a 2.2- to 3.4-mm increase in the aortic wall circumference per cardiac cycle. A similar increase was observed in luminal circumference, with a 2.4- to 3.6-mm increase per cycle. Conclusion: This study introduces the concept of dynamic cine CTA imaging of aortic motion, providing insight into the pathophysiology of abdominal aortic and iliac pulsations. Patients with AAAs selected for EVAR demonstrate changes in aortic circumference with each cardiac cycle that may have consequences for endograft sizing and future design. The potential for graft migration, intermittent type I endoleak, and poor patient outcome following EVAR can be anticipated. Complex aortic dynamics deserve increased scrutiny in an effort to prevent potential complications.

Endovascular aneurysm repair alters renal artery movement: a preliminary evaluation using dynamic CTA.

Purpose: To observe the natural renal artery motion during cardiac cycles in patients with abdominal aortic aneurysm (AAA) and how the implantation of stent-grafts may distort this movement. Methods: Data on 29 renal arteries from 15 male patients (mean age 72.6 years, range 66–83) treated with Talent or Excluder stent-grafts were acquired using an electrocardiographically (ECG)-gated dynamic 64-slice CT scanner. ECG-triggered retrospective reconstructions were made at 8 equidistant time points over the R-R cardiac cycle. The gated datasets were reconstructed perpendicular to the center flow lumen of each renal artery at 1.2 and 2.4 cm from the renal ostium. Center of mass displacement was determined per cardiac cycle for pre- and post-EVAR renal arteries and compared. Results: Normal renal artery motion in AAA patients was impressive, with up to 3-mm movement both near and distant from the aorta (mean 2.0±0.6 mm, range 1.1–3.0). EVAR inhibited proximal renal motion, resulting in a 31% decrease in maximal movement (mean 1.4±0.7 mm, range 0.7–2.0; p≤0.05). Distal renal artery motion was unaffected by EVAR, with motion similar to the pre-EVAR state. Conclusion: ECG-gated dynamic CTA is feasible on a 64-slice scanner with a standard radiation dose and can detect potentially serious consequences of EVAR. EVAR alters renal artery motion by limiting proximal motion while leaving distal motion unaffected.

Preliminary intraobserver and interobserver variability in wall stress and rupture risk assessment of abdominal aortic aneurysms using a semiautomatic finite element model

OBJECTIVE We investigated the intraobserver and interobserver variability of using semiautomatic finite element analysis to calculate the von Mises stress and peak wall rupture risk (PWRR) in patients with an abdominal aortic aneurysm (AAA) in longitudinal studies. METHODS Four independent observers made 3-dimensional (3D) reconstructions, with minimal manual adjustments, of small AAAs (<5.0 cm) in 17 patients and processed finite element analysis. We used semiautomatic diagnostic software with a finite element model (A4research, VASCOPS GmbH, Graz, Austria). The finite element method was used to calculate von Mises stress and PWRR, which are indicators for wall stress. The differences of each pair of measurements of von Mises stress and PWRR were plotted against their mean and the difference of the mean, according to Bland-Altman analysis. RESULTS The intraobserver variability had an overall mean percentage difference of 6.86% ± 6.46% for the von Mises stress and 7.70% ± 6.26% for PWRR. The interobserver variability for the four observers showed an overall mean percentage difference of 7.09% ± 6.16% for the von Mises stress and 9.47% ± 8.18% for the PWRR measurement. No significant differences were found (P < .05), for the von Mises stress and PWRR for all observers. CONCLUSIONS The von Mises stress and PWRR of small AAAs calculated in this semiautomatic finite element analysis program show good interobserver and intraobserver variability. It is suitable for clinical use to evaluate mechanical aortic wall characteristics and to compare it with other current methods such as maximum aortic diameter measurements.

Dynamic Cine-Computed Tomography Angiography Imaging of Standard and Fenestrated Endografts: Differing Effects on Renal Artery Motion

Different endograft configurations (fenestrated, transrenal, infrarenal) may varyingly affect aortic side branch movement. Renal artery motion was evaluated with 64-slice dynamic cine-computed tomography angiography before and after endovascular aneurysm repair in 16 patients (46 renal arteries). Center-of-mass displacement of the renals was determined per heartbeat for before repair for 3 different endografts; differences were compared, with significance at P < 0.5. Preoperative renal artery motion is significant (1.2 [SD 0.5] mm, range, 0.6-2.). Neither transrenal nor infrarenal endografts alter renal artery motion compared with before repair (P < .05). Renal artery motion after fenestrated endovascular repair with renal stents reduces motion to 25% of the preoperative value (0.3 [SD, 0.1] mm, range, 0.2-0.5 mm; P = .01). Endograft implantation without stented side branches does not change renal artery motion, potentially allowing significant movement of the renal artery relative to the fenestration. Routine stenting of fenestrations limits postoperative renal artery motion to 0.3 mm, thereby preventing significant branch movement in relation the fenestration.