Chris V. Ioannou

Geometrical Factors Influencing the Hemodynamic Behavior of the AAA Stent Grafts: Essentials for the Clinician

Endovascular aneurysm repair (EVAR) is considered to be the treatment of choice for abdominal aortic aneurysms (AAA). Despite the initial technical success, EVAR is amenable to early and late complications, among which the migration of the endograft (EG) with subsequent proximal endoleak (Type Ia) leads to repressurization of the AAA sac, exposure to excessive wall stress, and, hence, to potential rupture. This article discusses the influence that certain geometrical factors, such as neck angulation, iliac bifurcation, EG curvature, neck-to-iliac diameter, and length ratios, as well as iliac limbs configuration can exert on the hemodynamic behavior of the EGs. The information provided could help both clinicians and EG manufacturers towards further development and improvement of EG designs and better operational planning.

Technical Challenges Encountered During Deployment of the Ovation Abdominal Aortic Stent-Graft System

Purpose To describe technical challenges encountered using the Ovation endograft for abdominal aortic aneurysms and suggest tips and maneuvers for successful management. Technique Deployment of the Ovations unsupported main body is often associated with the anteroposterior arrangement of the limb gates instead of the usual side-by-side configuration, rendering contralateral catheterization challenging. Successful catheterization of the contralateral limb can be confirmed by lateral deviation of the ipsilateral stiff guidewire caused by balloon inflation within the contralateral limb. Moreover, failure to cannulate the contralateral limb gate due to persistent impingement of the guidewire or compromise of the inflated rings can be overcome using the transbrachial antegrade approach. Conclusion Awareness of certain aspects associated with the use of the Ovation device and adoption of the adjunctive techniques herein described helps the interventionist avoid unexpected challenges or manage technical difficulties to maximize the devices safety and effectiveness.

A Case of Difficult Catheterization of the Contralateral Limb of the Ovation Abdominal Stent Graft System in Challenging Aortoiliac Anatomy, Facilitated through the Brachial Access: A Word of Caution

The Ovation Stent Graft System is a new trimodular endoprosthesis for the treatment of abdominal aortic aneurysms. A long nitinol stent with anchors serves the suprarenal fixation, whereas inflatable rings in the main body achieve sealing. This dissociation precludes the presence of a nitinol skeleton in the endograft, thus, avoiding competing for the same space within the delivery system, enabling the latter to achieve ultra-low profiles. However, the lack of nitinol support may render the endografts docking limb prone to collapse in cases of narrow aortoiliac anatomy. We present a case of challenging contralateral limb catheterization, facilitated effectively through the brachial access. Preparing for the brachial route remains a useful and time-sparing adjunctive measure that guarantees the devices safety and effectiveness in challenging anatomies.

Applying findings of computational studies in vascular clinical practice: fact, fiction, or misunderstanding?

Applying Findings of Computational Studies in Vascular Clinical Practice : Fact, Fiction, or Misunderstanding?

Going Beyond Current AAA Neck Angulation Limitations of the Ovation Ultra-low Profile Polymer-filled Stent Graft

* Corresponding author. Vascular Surgery Unit, Department of Cardiothorac Heraklion, Greece. E-mail address: ioannou@med.uoc.gr (C.V. Ioannou). 1078-5884/ 2016 European Society for Vascular Surgery. Published by El http://dx.doi.org/10.1016/j.ejvs.2016.06.003 27 Maynar M, Qian Z, Hernandez J, Sun F, DeMiguel C, Crisostomo V, et al. An animal model of abdominal aortic aneurysm created with peritoneal patch: technique and initial results. Cardiovasc Intervent Radiol 2003;26(2):168e76.

The Chimney Technique with the Ovation Abdominal Stent Graft System: An Ideal Platform for Self-expandable Renal Stents?

Massmann and colleagues report on the successful treatment of two juxtarenal aneurysms with the chimney technique using the Ovation abdominal stent graft system (TriVascular, Santa Rosa, CA, USA) [1]. The described two patients had their lowermost renal artery stented with a balloonexpandable (Advanta V12, Atrium Medical Corporation, Hudson, NH) and a self-expandable (Fluency, Bard, Murray Hill, NJ) stent graft, respectively, whereas the small iliac vessels problem was easily encountered with the low-profile introduction system of the Ovation stent graft. As clearly depicted in Fig. 3 of the article, the vertical segment of the balloon-expandable stent graft run parallel to the Ovation’s segment proximal to the first inflatable ring, i.e., the segment where the basis of the suprarenal stent is attached, and thus exerts radial force. However, if one assumes a chimney case where both renal arteries are involved, then the Ovation endograft will be advanced more cephalad to accommodate the stent graft of the uppermost renal artery, leaving the lowermost inevitably engaged by the first inflatable ring [2]. The inflatable rings of Ovation stent graft exert a minor pressure of only 1 atm, whereas its deployment in not followed by inflation of a molding balloon [3]. Hence, synchronous kissing ballooning of both Ovation device and renal stent grafts is not required, avoiding compromising the flexible self-expandable stent grafts. In such case, a self expandable stent graft could be ideally ‘‘wrapped around’’ by the first inflatable ring. While balloon-expandable stent grafts can be precisely placed and exert high radial force, self-expandable stent grafts are available in various lengths and are quite floppy to adapt to vessel bending [4, 5]. Therefore, it would be interesting if the authors explained their rationale for choosing their stent graft types to combine with the Ovation device in the described cases.

The Chimney Technique with the Ovation Trivascular Device: New Kid on the Block!

To the Editor: Visceral artery aneurysms are uncommon pathologies. Surgical treatment options include exclusion, bypass, or simple ligation. Endovascular management includes stent graft placement and coil embolization. Although endovascular approach is the preferable option, the anatomy of the aneurysm is the most important parameter for the choice of treatment. Anatomic factors that impede endovascular treatment include the presence of important collateral branch vessels in the vicinity or arising from the aneurysm. Flow-diverting stents (FDSs), including the Cardiatis Multilayer Stent, represent a new treatment option for visceral artery aneurysms because of their unique characteristics. The largest published experience comes from use of FDSs in the visceral aneurysms. The results are very encouraging, with a significant percentage of aneurysm thrombosis and shrinkage during follow-up and without any branch vessel occlusion. A complication frequently encountered after implantation of the FDSs in the visceral vessels is stent thrombosis, with its incidence reaching 8.3% in the 30-day postoperative period. Fortunately, when stent thrombosis occurred in superior mesenteric, splenic, and hepatic arteries, there were no clinical consequences for the patients. Visceral arteries have a developed collateral network that can sometimes prevent organ ischemia in cases of acute occlusion. Possible reasons for FDSs thrombosis in visceral aneurysms include poor runoff and patients’ non compliancewith dual-antiplatelet therapy. Dual-antiplatelet therapy in the 30-day postoperative period has been used in most cases of treatment of visceral aneurysms with FDS. In the very interesting study by Zhang et al., the authors describe their experience with the use of multiple overlapping bare stents for endovascular visceral aneurysm repair. This technique has been used alternatively to multilayer stent placement, because the latter is not available in their country. In total, 24 patients with visceral aneurysms were treated. In 18-months followup, there was no aneurysm rupture and no branch vessel occlusion. Aneurysm exclusion was detected in 83% of the cases and shrinkage in 50%. In the study by Zhang et al., no case of stent thrombosis is reported. It would be very useful to know what antiplatelet or antithrombotic regime they have administered to the patients after multiple bare stent implantation for visceral aneurysms’ exclusion. The results of this study are very encouraging, although longer follow-up is needed for safer conclusions.

Descending Thoracic Aorta Bi-femoral Bypass for Aortoiliac Disease in Patients with a Hostile Abdomen

A 67-year-old male presented with disabling bilateral claudication caused by aortoiliac occlusion (progression of aortoiliac disease and iliac stent occlusion). Open transabdominal aortic surgery was considered high risk because of multiple previous open abdominal operations (trauma-related). A thoracic aorta to bi-femoral artery bypass was performed via a posterolateral thoracotomy using a bifurcated Dacron graft, tunnelled through the left retroperitoneal space via the diaphragm, passing behind the left kidney. Three-year follow-up indicated no symptom recurrence. The descending thoracic aorta can be used as an excellent inflow source for aortic repair in patients with extensive aortoiliac disease and a hostile abdomen.

Regarding “One-year outcomes from an international study of the Ovation abdominal stent graft system for endovascular aneurysm repair”

as coil embolization and stent placement for type V aneurysms, which was performed in two of their patients.Wewould like to elaborate on the coil embolization of dissecting aneurysms. There are many articles reporting the endovascular treatment of SIDSMA in recent years; many patients with dissecting aneurysms were treated by placement of self-expandable and open stents without coil embolization, andall of themwere discharged uneventfully.We believe that the dissecting aneurysm would thrombose and that the aneurysm size would be reduced after placement of a stent, with gradual resolution of the false lumen and improved remodeling with patencyof the true lumen.There likely exists a risk of ruptureof thedissecting aneurysmwith placement of coils, and the true lumenmay also be compressed if coils are used. Although the authors have a good result after coil embolization of the dissecting aneurysm in two patients, we think it may not be necessary to perform such embolization.

Finite element analysis methods in clinical practice: we have nothing to fear but fear itself!

Finite element analysis (FEA) method is a well-established numerical concept that divides any geometry into a large number of finite elements, which together can form an equivalent biomechanical model of an abdominal aortic aneurysm (AAA). The geometry of the reconstructed model, the systemic pressure, flow parameters (boundary conditions), and the constitutive assumptions determine the relationship and interaction between stress (mechanical loading) and strain (deformation) of the structure wall, which comprise the fundamental features of a FEA model and, hence, its theoretical utility. The influence that the constitutive assumptions (homogenous AAA wall thickness and isotropic constitutive properties) and the modeling techniques have on the results of the method, as well as the computationallydemanding equipment needed, remain the Achilles’ heel of the concept; yet, the most significant limitations are the lack of clinical validation and correlation of FEA findings with histopathological or biochemical data. The A4clinics software (VASCOPS GmbH, Graz, Austria) facilitates the aforementioned process since it allows a clinician to have the reconstructed FEA model (Figure, A) and the color contours with the values of both the peak wall stress (PWS) and the peak wall rupture index (PWRI) in an AAA (Figure, B), as illustrated here, within 20 minutes. The intraand interobserver variability of the method has been reported to be low. In this issue, Erhart et al. attempt to correlate FEA findings of 15 asymptomatic AAAs with histological specimens from areas of low and high PWS and PWRI. Within samples of each patient, the sites of low rupture index were associated with significantly more smooth muscle cells and elastin fibers than sites of higher PWRI, suggesting an increased local histological integrity in the former. Previous studies have demonstrated a positive correlation between FEA findings and increased uptake of 18F-FDG as a marker of local wall inflammation. Therefore, the important (and long anticipated!) results from Erhart et al. are not only in accord with previous experiments but also provide a direct, straightforward proof of the effects (histological degeneration) that hemodynamic loading exert on the AAA wall structure. However, AAAs of higher PWRI were not associated with higher tissue degeneration when compared to AAAs of lower PWRI in the study, implying that the attenuation of tensile strength to the point of rupture is a rather local phenomenon within each AAA, wherein biochemical parameters, such as oxidative stress and metalloproteinases, play crucial and determinant roles. So, it would be