Endovascular Aneurysm Repair Alters Renal Artery Movement: A Preliminary Evaluation Using Dynamic CTA

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1 476 J ENDOVASC THER CLINICAL INVESTIGATION Endovascular Aneurysm Repair Alters Renal Artery Movement: A Preliminary Evaluation Using Dynamic CTA Bart E. Muhs, MD 1 ; Arno Teutelink, MD 1 ; Matthias Prokop, MD, PhD 2 ; Koen L. Vincken, PhD 2 ; Frans L. Moll, MD, PhD 1 ; and Hence J.M. Verhagen, MD, PhD 1 Departments of 1 Vascular Surgery and 2 Radiology, University Medical Center, Utrecht, The Netherlands. 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 mm, range ). EVAR inhibited proximal renal motion, resulting in a 31% decrease in maximal movement (mean mm, range ; p0.05). 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. J Endovasc Ther Key words: endovascular aneurysm repair, renal artery motion, stent-graft, suprarenal fixation, dynamic computed tomographic angiography The human aorta and its renal side branches are part of a dynamic, pulsatile environment. Recent studies evaluating normal renal artery motion have documented significant distortions during the cardiac cycle. 1 3 Although breath-hold techniques can minimize respiration-induced renal artery motion, normal arterial pulsatility during the cardiac cycle can also produce motion. Draney et al. 2 analyzed renal artery bending during respiration using contrast-enhanced magnetic resonance angiography; their 3-dimensional (3D) analysis showed a maximum displacement of 13.2 mm between inspiration and expiration. Little attention has been given to renal artery motion in patients with infrarenal abdominal aortic aneurysms (AAA) or the consequences of EVAR on this motion. Arko et al. 4 The authors have no commercial, proprietary, or financial interest in any products or companies described in this article. Address for correspondence and reprints: Hence J.M. Verhagen, MD, PhD, Department of Vascular Surgery G , University Medical Center, PO Box 85500, 3508GA Utrecht, The Netherlands. Fax: ; H.Verhagen@ umcutrecht.nl 2006 by the INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS Available at

2 J ENDOVASC THER EVAR AND RENAL ARTERY MOTION 477 Figure 1Sagittal static CTA with lines illustrating the level at which measurements were made on dynamic cine CT images. Measurements were taken at 1.2 and 2.4 cm from the renal artery ostia. found that endovascular aneurysm repair (EVAR) results in substantial static changes in aneurysm and aortic morphologies, with a reported 15% increase in neck angulation and 27% decrease in neck length in large AAAs treated with stent-grafts. Moreover, alterations in renal artery dynamics may be involved in disease states, including intimal hyperplasia, renal artery stenosis, and atherosclerosis, which may have implications for future endograft designs. 5,6 We thus hypothesized that morphological changes might be observed when the renal artery is subjected to altered mechanical forces following EVAR. Although the traditional pre- and post- EVAR measurement of infrarenal AAAs has been carried out using static contrast-enhanced computed tomographic angiography (CTA), 7 10 we utilized a new diagnostic tool, dynamic CTA, to characterize preoperative renal artery motion in AAA patients during the cardiac cycle and evaluate the postoperative effect of EVAR on renal artery motion. METHODS The CT scans used for this study were obtained as part of the standard EVAR protocol at our institution; no patient was subjected to additional CT scanning or radiation exposure. The indications for EVAR and endograft selection were made by one surgeon, who performed all the procedures. Scans from 15 men (mean age 72.6 years, range 66 83) treated with Talent (n6) or Excluder (n3) stentgrafts were studied: 6 pre- and 9 pre/post- EVAR (not all patients had both pre- and postoperative scans). Data on 29 renal arteries were acquired using an electrocardiographically (ECG)-gated dynamic 64-slice CT scanner (Philips Medical Systems, Cleveland, OH, USA) during a single 20-s breath-hold phase in which the entire abdomen was imaged. The imaging protocol was set at mm collimation and a pitch of Radiation exposure parameters were 120 kv and 300 mas, which resulted in a CT dose index of 21 mgy. Intravascular nonionic contrast (120 ml of Imerol 300; Schering, Berlin, Germany) was injected at a flow rate of 4 ml/s followed by a 50-mL bolus saline chaser. The scan was started using bolus triggering software with a threshold of 100 HU over baseline. The dataset of each patient was loaded into a separate workstation (Extended Brilliance Workspace; Philips Medical Systems) and processed using the cardiac review program function. 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 (Fig. 1). Measurements were taken in relation to the reference point at each time point during the cardiac cycle. Center of mass (COM) was plotted on a Cartesian coordinate system, and maximal COM displacement was determined per cardiac cycle for pre- and post-evar renal

3 478 EVAR AND RENAL ARTERY MOTION J ENDOVASC THER Figure 2Mean maximum center of mass displacement during the cardiac cycle in AAA patients prior to EVAR at 1.2 cm (proximal) and 2.4 cm (distal) from the renal ostium. There is no difference in COM movement between the 2 levels (pns). arteries. Data are presented as the mean standard deviation. Pre- and post-evar renal movement was compared using a Student t test, with p0.05 considered significant. RESULTS Image acquisition was rated as good to excellent by the observers. Renal artery motion in patients with infrarenal aneurysms was impressive, with up to 3 mm maximal movement both near and distant from the aorta (mean mm, range ; Fig. 2). Maximal COM displacement did not necessarily occur in the anterior-posterior or sagittal planes. Renal artery motion existed in a 3D environment with complex movement and conformation changes. EVAR with suprarenal fixation significantly inhibited proximal physiological renal motion (Fig. 3A), resulting in a 31% decrease in maximal movement (mean mm, range ; p0.05). Distal renal artery motion was unaffected by EVAR, with motion similar to the pre-evar state (Fig. 3B). Figure 3(A) Mean maximum COM displacement during the cardiac cycle at 1.2 cm from the renal ostium pre- and post-evar. There is a significant decrease in COM movement following EVAR (p0.05). (B) Mean maximum COM displacement during the cardiac cycle at 2.4 cm from the renal ostium pre- and post-evar. There is no difference in movement at this level following EVAR (pns). DISCUSSION We observed preoperative renal artery motion of 1 to 3 mm in proximal (1.2 cm) and distal (2.4 cm) locations along the renal artery in patients with infrarenal aneurysms. With up to 3 mm movement per cardiac cycle occurring over millions of heart beats, it is conceivable that renal artery motion may play a causative role in renal artery stent fractures. 6,7 Multiple authors have examined renal function following EVAR Although our study did not look at this aspect, we demonstrated that the presence of an endograft has dynam-

4 J ENDOVASC THER EVAR AND RENAL ARTERY MOTION 479 ic consequences for the renal arteries. Whether or not this has functional implications remains unknown at this time. Our preliminary study was designed to determine if EVAR affected preoperative renal motion; it was not powered to elucidate differences between stent-graft designs. Future studies evaluating potential differences between stent-grafts are anticipated. We have shown that EVAR alters renal artery motion only at the 1.2-cm point; at 2.4 cm from the renal artery ostium, motion is unaffected by EVAR. Changes in angles, bending, and complex (3D) changes in configuration are taking place. Perhaps the presence of a relatively stiff device placed adjacent to a moving renal artery pins the proximal renal artery, thus limiting motion, while the more distal renal artery is of sufficient distance from the endograft to minimize the motionlimiting effect. We selected 1.2 and 2.4 cm distances based on our preliminary analysis of maximal motion and because these distances are relevant anatomical points for fenestrated and branched endografts, which are emerging as complex AAA treatment options. Renal fenestrated and branched endografts typically employ renal stents 2.4 cm long but greater than 1.2 cm in length. 17,18 The endpoint of a renal stent in these complex cases would fall somewhere between our measured distances and within a maximal area of arterial conformational change. Endografts with stiff renal side branches may induce further alteration in renal artery motion. The consequences on renal stent durability, progression or initiation of renal disease, and potential for endoleaks are unknown. However, our observations raise concern, which is strengthened by early reports of significant renal insufficiency following fenestrated endografting. 19,20 Conclusion ECG-gated dynamic CTA is feasible on a 64- slice scanner and provides insight into renal motion before and after EVAR. AAA stentgraft repair appears to change renal artery movement by limiting proximal renal artery motion while leaving distal motion unaffected. Any ill consequences of these complex dynamic renal artery changes are presently unknown, but with fenestrated and branched stent-grafts emerging, issues of stent durability, fixation systems, and long-term renal artery effects should be considered. REFERENCES 1. Vasbinder GB, Maki JH, Nijenhuis RJ, et al. Motion of the distal renal artery during three-dimensional contrast-enhanced breath-hold MRA. J Magn Reson Imaging. 2002;16: Draney MT, Zarins CK, Taylor CA. Three-dimensional analysis of renal artery bending motion during respiration. J Endovasc Ther. 2005;12: Kaandorp DW, Vasbinder GB, de Haan MW, et al. Motion of the proximal renal artery during the cardiac cycle. J Magn Reson Imaging. 2000; 12: Arko FR, Filis KA, Hill BB, et al. Morphologic changes and outcome following endovascular abdominal aortic aneurysm repair as a function of aneurysm size. Arch Surg. 2003;138: Bessias N, Sfyroeras G, Moulakakis KG, et al. Renal artery thrombosis caused by stent fracture in a single kidney patient. J Endovasc Ther. 2005;12: Sahin S, Memis A, Parildar M, et al. Fracture of a renal artery stent due to mobile kidney. Cardiovasc Intervent Radiol. 2005;28: Gomes MN, Davros WJ, Zeman RK. Preoperative assessment of abdominal aortic aneurysm: the value of helical and three-dimensional computed tomography. J Vasc Surg. 1994;20: Filis KA, Arko FR, Rubin GD, et al. Three-dimensional CT evaluation for endovascular abdominal aortic aneurysm repair. Quantitative assessment of the infrarenal aortic neck. Acta Chir Belg. 2003;103: Siegel MJ. Multiplanar and three-dimensional multi-detector row CT of thoracic vessels and airways in the pediatric population. Radiology. 2003;229: Rubin GD, Schmidt AJ, Logan LJ, et al. Multidetector row CT angiography of lower extremity arterial inflow and runoff: initial experience. Radiology. 2001;221: Malina M, Lindh M, Ivancev K, et al. The effect of endovascular aortic stents placed across the renal arteries. Eur J Vasc Endovasc Surg. 1997; 13: Malina M, Brunkwall J, Ivancev K, et al. Renal

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