Leonard W. Tse

Radiofrequency In Situ Fenestration for Aortic Arch Vessels During Thoracic Endovascular Repair

Purpose: To report the first clinical application of a novel technique using radiofrequency puncture to create retrograde in situ fenestrations during thoracic endovascular aortic repair (TEVAR). Methods: Between June 2011 and December 2013, 40 TEVAR procedures were performed in our facility, including 10 cases in which in situ fenestration was planned. Two thoracic stent-graft models were deployed: the Valiant (n=5) and the Zenith TX2 (n=5). A 0.035-inch PowerWire radiofrequency guidewire delivered from a brachial approach was used to fenestrate the grafts covering a left subclavian artery (LSA) in 9 cases and a left common carotid artery in one. The fenestrations were serially dilated to 6 mm, and self-expanding Advanta V12 covered stents were positioned in the target arteries. Results: Technical success was achieved in 6 of the 10 planned cases. Of the remaining 4 cases, stent-grafts were deployed in zone 3 in 2 cases (one received a chimney to the LSA). Another stent-graft was deployed in zone 2 without endoleak after fenestration was abandoned (the LSA had good filling via the vertebral artery). In the last case, the fenestration was unsuccessful in double-layered (proximal extension overlap) stent-grafts; a carotid-axillary bypass was required. There were no fenestration-related complications, but overall surgical complications included a case of paraparesis that resolved following spinal drainage and a death from a preexisting aortoesophageal fistula. There were no postoperative strokes. All fenestrations remained patent, and there were no endoleaks at a mean 12-month follow-up (range 1–33). Conclusion: Radiofrequency puncture is a viable alternative to needle or laser punctures for in situ fenestration during TEVAR. Early clinical results suggest technical feasibility and acceptable early outcomes.

Thoracic Aortic Frontier: Review of Current Applications and Directions of Thoracic Endovascular Aortic Repair (TEVAR)

Thoracic endovascular aortic repair, a minimally invasive technique is replacing the maximally invasive gold standard of thoracotomy and replacement of the descending thoracic aorta. With experience, indications have expanded to encroach on the arch and even ascending aorta. This review highlights the current state of technology, discusses controversies, and takes the perspective of a forward-thinking review to describe novel, innovative techniques that might make the entire thoracic aorta amenable to minimally invasive repair.

Radiofrequency Perforation System for in Vivo Antegrade Fenestration of Aortic Stent-Grafts

Purpose: To evaluate the ability to create in vivo antegrade fenestrations (IVAF) using a radiofrequency probe in juxtarenal aortic stent-grafts to preserve the patency of renal arteries. Methods: Modified stent-grafts with an unsupported fenestration area were deployed in the juxtarenal aorta of 2 25-kg dogs. Prior to deployment, both renal arteries were marked with detachable coils that were later removed (dog 1) or with hydrophilic catheters (dog 2). After deployment, a radiofrequency probe was used to perforate the graft. If puncture was successful, attempts were made to pass guidewires into the renal arteries for balloon dilation and stenting of the graft perforation. Doppler ultrasound scans of the renal arteries were taken after 1 week. Doppler ultrasound and angiography were repeated prior to autopsy and macroscopic analysis at 1 month. Results: Fenestration was attempted in 3 renal arteries (1 in dog 1 and 2 in dog 2). It was successful in 2 renal arteries but required 6 attempts in dog 1 and 3 in dog 2. The failed case was related to the position of a stent-graft strut close to the fenestration area. One stent thrombosis was seen during follow-up, while the other fenestrated artery remained patent. No stent fracture was encountered during follow-up. Conclusion: This radiofrequency device allowed successful fenestration but was difficult to control. Technical improvements are required to improve clinical success and patency.

Increasing angulation decreases measured aortic stent graft pullout forces

OBJECTIVE Experimentally measured pullout forces for stent grafts (SGs) are used in clinical discussions and as reference values in bench studies and computer simulations. Previous values of these forces are available from studies in which the SG was pulled out in the straight caudal direction. However, clinical and numerical studies have suggested that displacement forces acting on SGs are directed more anteriorly. The objective of this study was to measure pullout forces as a function of angulation and to test the hypothesis that pullout forces decrease with increasing angulation. METHODS Six different SGs (Bolton Treovance, Cook Zenith Flex, Cook Zenith LP, Medtronic Endurant, Medtronic Talent, and Vascutek Anaconda) were deployed in fresh bovine aortas, then pulled out by an electronic motor at 1 mm/s, while tension force was measured continuously with a digital load cell. The SG off-axis angulation was changed from 0 to 90 degrees in increments of 10 degrees. The test system was submerged in a custom-built temperature-controlled saline bath at 37°C. At least three tests were performed for each device at each angle (with the exception of the Cook Zenith Flex, which experienced plastic deformation of its barbs after a single test per device). Each aortic specimen was used only once and then discarded. Hand-sutured graft anastomoses were also tested at 0 degrees to provide a reference value. RESULTS A total of 374 pullout tests were performed for the SGs and anastomoses. Sixty-four tests were excluded because of failure of the aorta or apparatus before device pullout. The remaining 310 tests showed pullout forces that demonstrated a decrease in the average pullout force for all six devices from 0 to 90 degrees (Bolton Treovance from 39.3 N to 23.9 N; Cook Zenith Flex from 59.8 N to 48.9 N; Cook Zenith LP from 50.3 N to 41.8 N; Medtronic Endurant from 29.9 N to 25.8 N; Medtronic Talent from 6.0 N to 5.5 N; and Vascutek Anaconda from 37.0 N to 30.3 N). For reference, the mean pullout force for the hand-sutured anastomoses was 63 N. CONCLUSIONS This study reports for the first time the change in pullout force with angulation, showing a general pullout force decrease with increasing angle. With a larger number of samples than in previous studies, our results provide updated benchmark data that can be used for clinical discussions, computational and experimental studies, and future device design.

Effects of Pulsatile Fatigue on In Situ Antegrade Fenestrated Polyester Stent Grafts Deployed in a Patient-Specific Phantom Model of Juxtarenal Aortic Aneurysm

PURPOSE To evaluate the effects of in situ fenestration on the fabric of stent grafts deployed in a patient-specific phantom of a juxtarenal abdominal aortic aneurysm. MATERIALS AND METHODS Four patient-specific juxtarenal abdominal aortic aneurysm polyurethane models were created, and bifurcated Zenith (Cook, Inc, Bloomington, Indiana) and Endurant (Medtronic, Minneapolis, Minneapolis) endografts were deployed into the models, covering the renal arteries. Antegrade in situ fenestration was carried out with radiofrequency puncture followed by balloon dilation with either conventional or cutting balloons. Renal covered stents were deployed and flared. Specimens were mounted onto an accelerated fatigue tester for 40M cycles (1 patient life-year), and evaluated with microscopy, caliper measurements, and fabric counts. RESULTS Cutting balloons resulted in more fabric fraying. None of the fenestrations grew beyond the targeted 6-mm diameter despite accelerated fatigue. Fluoroscopic images demonstrated a very prominent waist of the renal fenestration in the Cook device when a conventional balloon was used compared with a cutting balloon. The average fenestration diameter for the Cook device was only 3.1 mm with the conventional balloon compared with 4.8 mm with the cutting balloon. The average fenestration diameter for the Medtronic device was 3.8 mm with the conventional balloon compared with 5.1 mm with the cutting balloon. The fabric counts suggested crowding of yarns around the fenestrations with conventional balloons but less with cutting balloons. CONCLUSIONS This experimental work suggests that the size of in situ renal fenestrations does not expand beyond the target diameter despite cyclic fatigue. Although the small number of devices tested and selected aortorenal anatomy in this study may limit conclusions, textile analysis suggests that cutting balloons should be used for the Cook Zenith device, whereas conventional balloons should be used for the Medtronic Endurant device when performing in situ fenestration.

Bridging stent-graft pullout force analysis.

Purpose To assess the pullout force (POF) of bridging stent-grafts used in thoracoabdominal stent-grafts and iliac bifurcated grafts. Methods In an experimental setup, the POFs of Viabahn or Fluency with or without a Zilver stent were measured when deployed into the renal and celiac branches of a Zenith thoracoabdominal cuff-bearing branched stent-graft. The POFs of the Atrium i-Cast, Viabahn, Fluency, and Fluency+Zilver were measured when deployed into an iliac bifurcated graft with a short side-branch for the internal iliac artery. At least 10 trials were performed for each stent in air at room temperature. Results The median POF (IQR; absolute range) required to dislodge each bridging stent-graft from the 6-mm renal branch was 1.89 N (0.47 N; 1.65–2.5) for the 7-mm Viabahn, 1.17 N (0.39 N; 0.68–1.57 N) for the 7-mm Fluency, and 2.08 N (0.49 N; 1.59–2.62 N) for the 7-mm Fluency with a supporting 8-mm Zilver stent (p<0.001). For the 8-mm celiac branch, the POFs were 2.79 N (0.82 N; 2.31–4.16 N), 1.74 N (0.18 N; 1.51–1.91 N), and 2.73 N (0.94 N; 1.9–3.61 N) for the 9-mm Viabahn, 9-mm Fluency, and 9-mm Fluency with a 10-mm Zilver stent, respectively (p<0.001). For the 8-mm internal iliac branch, the POFs were 3.53 N (0.85 N; 2.55–4.72 N) for the 9-mm i-Cast, 3.82 N (0.41 N; 3.29–4.45 N) for the 9-mm Viabahn, 2.32 N (0.23 N; 1.63–2.64 N) for the 9-mm Fluency, and 2.61 N (0.71 N; 1.65–3.63 N) for the 9-mm Fluency with a 10-mm Zilver stent (p<0.001). Conclusion There is a small but significant difference in pullout forces among various bridging stent-grafts. As pullout forces may be one factor contributing to type III endoleaks in complex endovascular repairs involving fenestrated and branched stent-grafts, further study is warranted to compare these grafts clinically to determine if they perform differently. According to this study, the theoretical advantages associated with the Viabahn stent-graft make it a strong choice for minimizing branch dislocations.

Analysis of Iliac Artery Geometric Properties in Fenestrated Aortic Stent Graft Rotation

Introduction: A complication of fenestrated endovascular aneurysm repair is the potential for stent graft rotation during deployment causing fenestration misalignment and branch artery occlusion. The objective of this study is to demonstrate that this rotation is caused by a buildup of rotational energy as the device is delivered through the iliac arteries and to quantify iliac artery geometric properties associated with device rotation. Methods: A retrospective clinical study was undertaken in which iliac artery geometric properties were assessed from preoperative imaging for 42 cases divided into 2 groups: 27 in the nonrotation group and 15 in the rotation group. Preoperative computed tomography scans were segmented, and the iliac artery centerlines were determined. Iliac artery tortuosity, curvature, torsion, and diameter were calculated from the centerline and the segmented vessel geometry. Results: The total iliac artery net torsion was found to be higher in the rotation group compared to the nonrotation group (23.5 ± 14.7 vs 14.6 ± 12.8 mm−1; P = .05). No statistically significant differences were found for the mean values of tortuosity, curvature, torsion, or diameter between the 2 groups. Conclusion: Stent graft rotation occurred in 36% of the cases considered in this study. Cases with high iliac artery total net torsion were found to be more likely to have stent graft rotation upon deployment. This retrospective study provides a framework for prospectively studying the influence of iliac artery geometric properties on fenestrated stent graft rotation.

Toothpick-induced aortoenteric fistula presenting as sepsis

Aortoenteric fistulas (AEF) are a rare but life-threatening cause of gastrointestinal (GI) bleeding. We present the case of a primary AEF caused by ingestion of a toothpick by a 47-year-old male. This is the 10th known case in the literature in which a foreign body was found to be the cause of a communication between the aorta and the GI tract. Most foreign objects have been sewing needles; this is the first known case of a toothpick penetration. The patient presented to our institution with polymicrobial sepsis and bilateral pulmonary septic emboli. The patient was successfully treated but required multiple interventions and a prolonged intensive care unit admission.

‘In-stock’ fenestrated stent graft for the urgent repair of an abdominal aortic aneurysm

Endovascular aneurysm repair (EVAR) is a minimally invasive method for the treatment of abdominal aortic aneurysms; however, the implementation of this technique is often limited by the aortic pathology, especially in the urgent or emergent setting. An 82-year-old male with a 7.3 cm symptomatic juxtarenal aneurysm presented at our centre for assessment. He was diagnosed as a high-risk candidate for open repair and therefore, not suitable for a conventional EVAR. Fortunately, a custom two-vessel fenestrated stent graft, which was originally constructed for another patient, was available. This device was implanted with no complications and all branches remain unobstructed; clear of aneurysms at 1 year. We present the use of ‘in-stock’ fenestrated grafts as a potential option to be considered in the urgent or emergent repair of abdominal aortic aneurysms.

Commentary: first clinical case of antegrade in situ fenestration of an aortic stent-graft.

In this issue of the JEVT, Dr. Wheatley describes antegrade in situ fenestration of a limb of a conventional bifurcated polytetrafluoroethylene (PTFE) aortic stent-graft to preserve the left internal iliac artery (IIA). This was performed for inadvertent IIA coverage in a patient with a previously-treated thoracic aortic dissection to maximize spinal collateral flow. Follow-up at 6 years showed a patent IIA and no endoleak. This article appears to be the first published case of in situ antegrade fenestration in a clinical setting. While there are many clinical reports regarding retrograde fenestration, there are very few regarding antegrade fenestration, and these have all been animal studies. The antegrade approach is much more challenging than the retrograde approach due to the issues of landmarking, guidance, and puncture support. The retrograde approach naturally mitigates these difficulties because of the direct access to the target vessel. In Dr. Wheatley’s case, it was serendipitous that everything was in place for an antegrade fenestration after the inadvertent IIA coverage. It was fortunate that the mechanical reentry catheter was used because other puncture devices, such as radiofrequency catheters, have not been as effective in penetrating ePTFE material (unpublished data). Mechanical puncture using needles and re-entry devices is certainly more challenging in tortuous anatomy because of the inability to directly translate force applied at the user end, as was demonstrated in this case where balloon support was needed to achieve puncture. The use of energy devices, such as laser or radiofrequency, has the advantages of minimizing the mechanical force required for puncture and being able to handle tortuous anatomy. However, it is not clear how various graft materials will respond to different puncture or dilation techniques. For example, the woven fabric from one manufacturer may respond differently to a cutting balloon compared to a conventional balloon. The optimal technique for in situ fenestration will vary for different graft materials and anatomical configurations (i.e., tortuosity and antegrade or retrograde approaches). To help physicians decide on the optimal technique, reports such as this add to the knowledge that is available through the literature. Both antegrade and retrograde in situ fenestration are clearly off-label alterations of stent-graft devices. However, it is likely that the techniques may continue to be used for salvage situations, as in this case, or emergencies that cannot be treated with off-theshelf devices due to anatomical, resource, or logistical reasons. This may be particularly relevant in the case of retrograde in situ fenestration in the aortic arch. In the rare but emergent case that presents a salvage situation, it may be helpful to draw from others’