The effects of crossing porcine renal artery ostia with various endovascular stents

A High Resolution MRI Study of the Relationship Between Plaque Enhancement and Perforator Stroke after Stenting for Symptomatic Vertebrobasilar Artery Stenosis

BACKGROUND AND PURPOSE

Perforator stroke is one of the most common complications of vertebrobasilar arterial stenting. We investigated whether perforator stroke after vertebrobasilar arterial stenting is associated with plaque enhancement in patients with severe vertebrobasilar artery stenosis.

METHODS

We studied patients with symptomatic vertebrobasilar arterial stenosis who underwent stenting from January 2017 to July 2020. Patients who underwent high resolution magnetic resonance imaging were recruited among them. Demographic data, risk factors of atherosclerosis, procedure details, and characteristics of imaging were extracted from electronic health records and imaging data. Plaque features were investigated by high resolution magnetic resonance imaging.

RESULTS

136 patients were enrolled in this study, 39 of whom fulfilled the inclusion criteria. 18 patients (46.2%) had obvious plaque enhancement among the 39 patients, and 21 (53.8%) had plaque non-enhancement. 21 patients (53.8%) had diffuse distribution, and 22 patients (56.4%) had irregular plaques surface. Patients were divided into plaque enhanced and plaque non-enhanced groups according to the degree of plaque enhancement. Clinical characteristics and other plaque features were similar between two groups. Procedure-related perforator stroke was identified in 4 patients (10.3%). Patients with plaque enhancement were more likely to have perforator stroke after stenting compared with those with plaque non-enhancement (22.2% versus 0%, P = 0.037).

CONCLUSIONS

Plaque enhancement in high resolution magnetic resonance imaging may be associated with perforator stroke after vertebrobasilar artery stenting.

A Permanent Common Carotid Filter for Stroke Prevention in Atrial Fibrillation: Ex Vivo and In Vivo Pre-Clinical Testing

BACKGROUND AND PURPOSE

A novel, permanent, bilateral, common carotid artery (CCA) coil filter implant was designed to capture stroke-producing emboli in atrial fibrillation patients. Under ultrasound guidance, it is automatically deployed through a 24-guage needle and is retrievable up to 4 h post-procedure. We assessed the feasibility, safety, and effectiveness of the CCA filter in pre-clinical testing.

METHODS

In a pulsatile flow simulator, the filter's embolic capture efficiency and integrity of simulated (1.2 mm diameter nylon balls) and actual thromboemboli were tested. Implant insertion, retrieval, and chronic safety were tested in sheep by ultrasound and X-ray. At termination, the CCAs were explanted and examined by pathology, histopathology and scanning electron microscopy. The fate of captured emboli was evaluated in sheep 3 weeks after upstream injection of autologous thromboemboli.

RESULTS

In the flow simulator, 10 filters captured 29 of 29 (100%) 1.2 mm diameter nylon balls. In the thromboemboli integrity test, all captured thromboemboli (99 of 99) were adherent to the filter, without fragmentation. All sheep (n = 30/60 implants) underwent successful CCA filter implantation. During follow-ups at 4, 12, 13, 23, and 31 weeks (6 sheep/12 implants at each follow-up), there were no (0%) major bleeds, CCA damage/stenosis, implant migration, flow obstruction, or thrombi detected by ultrasound. Two organized microthrombi (<100 μm) were observed by histopathology at the puncture site. After 3 weeks, autologous captured thromboemboli (n = 10) either completely regressed (5 of 5) or did not progress (5 of 5).

CONCLUSION

These favorable pre-clinical results prompt clinical testing of the CCA filter in stroke prevention clinical trials.

Correlation Studies and Literature Review of Medullary Artery Occlusion After Intracranial Vertebral Artery Stenting

BACKGROUND

Stenosis of the target intracranial vertebral artery is one of the major causes of posterior circulation ischemic stroke. The objective of this paper is to explore methods for reducing the occurrence of medullary artery occlusion after intracranial vertebral artery stenting.

CASE DESCRIPTION

The current research presents a retrospective analysis of 48 patients who received Gateway-Wingspan stent angioplasty to treat severe stenosis of the intracranial vertebral artery, evaluates the results of stenosis remission and perfusion improvement after stent angioplasty, and explores the causes of postoperative medullary artery occlusion. A total of 49 Wingspan stents were implanted in the 48 patients, with a surgical success rate of 100%. After stent implantation, the patients' rates of intracranial vertebral artery stenosis dropped from 75.9% ± 6.3% to 28.4% ± 5.1%. Transcranial Doppler or cranial computed tomography angiography 3 months after surgery showed that none of the patients suffered from in-stent restenosis. Within 24 hours after surgery, medullary perforating artery occlusion occurred in 2 patients, probably because atherosclerotic plaque in the stenotic area became less stable and displaced under the mechanical action of postoperative saccule and stent. As a result, the medullary artery was blocked. After drug and rehabilitation therapies, the patients' symptoms were alleviated.

CONCLUSIONS

Perforating artery occlusion after intracranial vertebral artery stenting can be prevented by strict assessment and preparation before surgery, correct choices of saccule and stent during operation, and other measures. However, large sample data are needed for verification.

Incidence of Renal Infarctions after Endovascular AAA Repair: Relationship to Infrarenal versus Suprarenal Fixation

Purpose:

To analyze the incidence and etiology of renal infarctions following endovascular abdominal aortic aneurysm (AAA) repair detected on computed tomography (CT) and determine any association with infrarenal versus suprarenal fixation.

Methods:

Between August 1994 and October 2001, 663 patients (604 men; mean age 68.5 years, range 40–98) underwent endovascular AAA repair with predominately bifurcated (505, 77%) stent-grafts. About a third (202, 30%) of the devices were deployed in a suprarenal position. Contrast-enhanced CT scans were performed on days 10, 90, and 365 after operation and then annually. Two radiologists blinded to procedural details compared the preoperative and postoperative scans to identify renal infarctions from inadvertent renal artery occlusion by the endograft. Only patients with inadvertent infarctions were analyzed relative to endograft fixation position and stent-graft type.

Results:

Mean follow-up was 37 months (range 0.1–75). Overall renal infarction rate was 11.9% (n=79); 23 (3.4%) patients suffered from limited, segmental infarction due to intentional covering of preoperatively diagnosed accessory renal arteries. Unintentional renal ischemia was identified in 56 (8.5%) patients. In this subgroup, 39 (19%) were observed in the 202 patients with suprarenal fixation versus 17 (3.7%) in the 461 stent-grafts positioned infrarenally (RR 3.35, 95% CI 2.20 to 5.04, p < 0.00001). There was a significant correlation between the incidence of infarction and the device type (14.3% for modular grafts versus 5.6% for unibody designs, p = 0.0002). Seventeen (2.6%) patients suffered from unilateral kidney loss, with dialysis required in 2 cases. Creatinine and urea showed no significant postoperative elevation in the overall patient population, but both levels were significantly (p < 0.02) elevated in patients with complete unilateral renal infarcts.

Conclusions:

Transrenal fixation of aortic endografts had a 3-fold higher risk for renal infarction in this large patient population. There is no significant difference for specific endografts, but modular designs were associated with a higher rate of renal infarction. The need to occlude preoperatively diagnosed accessory renal arteries with an endograft should be considered a contraindication for current available devices.

Improvement in Proximal Aortic Endograft Fixation: An Experimental Study Using Different Stent-Grafts in Human Cadaveric Aortas

Purpose:

To compare the proximal fixation characteristics of different types of stent-grafts (SG) and the adjunctive effect of a proximally placed Palmaz stent.

Methods:

Human cadaveric aortas were obtained at autopsy and cut into 30 aortic segments. Appropriately oversized (10% to 20%) commercial stent-grafts (Zenith, Ancure, Excluder, Talent) and 4 configurations of homemade Palmaz-based stent-grafts (polytetrafluoroethylene or polyester coverings each with no uncovered proximal edge or a 20-mm bare section of stent) were implanted 20 mm into an aortic segment and balloon dilated. Each segment was placed in an experimental apparatus to measure the dislodgment force. Bare Palmaz stents were used to reinforce the proximal fixation of the commercial stent-grafts, and the measurements were repeated. Manual anastomoses were made and their dislodgment force tested for comparison.

Results:

The median dislodgment force ranged from 6.5 N for the Excluder to 26.5 N for the Zenith (8.0 N for the Talent, 11.8 N for the Ancure, and 8.1 to 10.7 N for the various Palmaz stent-graft designs). There was no significant difference between the Zenith and the Ancure groups or between the Excluder and the Talent groups. However, the Zenith and Ancure devices required significantly higher (p = 0.0004) force (∼25%) to displace them than the other stent-grafts tested. With the Palmaz stent added to the proximal attachment site, the median dislodgment force for the different commercial endografts was significantly improved for all devices (p < 0.03): 34% for the Zenith device, 69% for the Ancure, 73% for the Talent, and 80% for the Excluder endoprosthesis.

Conclusions:

The Zenith stent-graft had the best resistance to dislodgment. An additional Palmaz stent placed at the proximal attachment site greatly improves endograft fixation regardless of the type of stent-graft. For complex aneurysm necks or for intraoperative type I endoleak management, an adjunctive Palmaz stent could be used.

Computational modeling of shear-based hemolysis caused by renal obstruction

As endovascular treatment of abdominal aortic aneurysms (AAAs) gains popularity, it is becoming possible to treat certain challenging aneurysmal anatomies with endografts relying on suprarenal fixation. In such anatomies, the bare struts of the device may be placed across the renal artery ostia, causing partial obstruction to renal artery blood flow. Computational fluid dynamics (CFD) was used to simulate blood flow from the aorta to the renal arteries, utilizing patient-specific boundary conditions, in three patient models and calculate the degree of shear-based blood damage (hemolysis). We used contrast-enhanced computed tomography angiography (CTA) data from three AAA patients who were treated with a novel endograft to build patient-specific models. For each of the three patients, we constructed a baseline model and endoframe model. The baseline model was a direct representation of the patient's 30-day post-operative CTA data. This model was then altered to create the endoframe model, which included a ring of metallic struts across the renal artery ostia. CFD was used to simulate blood flow, utilizing patient-specific boundary conditions. Pressures, flows, shear stresses, and the normalized index of hemolysis (NIH) were quantified for all patients. The overall differences between the baseline and endoframe models for all three patients were minimal, as measured though pressure, volumetric flow, velocity, and shear stress. The average NIH across the three baseline and endoframe models was 0.002 and 0.004, respectively. Results of CFD modeling show that the overall disturbance to flow caused by the presence of the endoframe struts is minimal. The magnitude of the NIH in all models was well below the accepted design and safety threshold for implantable medical devices that interact with blood flow.

Changes in inflammatory response after endovascular treatment for type B aortic dissection

This present study aims to investigate the changes in the inflammatory markers after elective endovascular treatment of Type B aortic dissection with aneurysm, as related to different anatomical features of the dissection flap in the paravisceral perfusion. Consecutive patients with type B aortic dissections with elective endovascular stent graft repair were recruited and categorized into different groups. Serial plasma levels of cytokines (Interleukin-1β, -6, -8, -10, TNF-α), chemokines (MCP-1), and serum creatinine were monitored at pre-, peri- and post-operative stages. The length of stent graft employed in each surgery was retrieved and correlated with the change of all studied biochemical parameters. A control group of aortic dissected patients with conventional medication management was recruited for comparing the baseline biochemical parameters. In total, 22 endovascular treated and 16 aortic dissected patients with surveillance were recruited. The endovascular treated patients had comparable baseline levels as the non-surgical patients. There was no immediate or thirty day-mortality, and none of the surgical patients developed post-operative mesenteric ischaemia or clinically significant renal impairment. All surgical patients had detectable pro-inflammatory mediators, but none of the them showed any statistical significant surge in the peri-operative period except IL-1β and IL-6. Similar results were obtained when categorized into different groups. IL-1β and IL-6 showed maximal levels within hours of the endovascular procedure (range, 3.93 to 27.3 higher than baseline; p = 0.001), but returned to baseline 1 day post-operatively. The change of IL-1β and IL-6 at the stent graft deployment was statistically greater in longer stent graft (p>0.05). No significant changes were observed in the serum creatinine levels. In conclusion, elective endovascular repair of type B aortic dissection associated with insignificant changes in inflammatory mediators and creatinine. All levels fell toward basal levels post-operatively suggesting that thoracic endovascular aortic repair is rather less aggressive with insignificant inflammatory modulation.

Placement of endovascular stent across the branching arteries: long-term serial evaluation of stent-tissue responses overlying the arterial orifices in an experimental study

PURPOSE

This study was designed to investigate the effects of stenting across the branching arteries on the patency and stent-tissue responses over the branching arterial orifices.

METHODS

Thirteen dogs were observed after placing aortic stents across the celiac arteries (CA), superior mesenteric arteries (SMA), and renal arteries (RA). The animals were grouped according to stent types: large-cell group (n = 6) and small-cell group (n = 7). Angiography was performed to evaluate the branching artery patency at 2, 6, and 12 months after stent insertion, and the stent-tissue responses covering the orifices were evaluated on histopathologic examination.

RESULTS

All branching arteries were patent on follow-up angiography; however, three patterns of stent-tissue responses over the orifices were observed: neointimal layering, bridging septa, and papillary hyperplasia. Although neointimal layering and bridging septa were evenly observed, severe papillary hyperplasia was more frequent at SMA and CA than RA. Four RA showed less than 50% ostial patency, and localized infarct was observed in six kidneys (24%). The ostial patency tended to decrease with small-cell stent during the follow-up period.

CONCLUSIONS

Various stent-tissue responses over the branching artery orifices are induced by the aortic stent covering the branching arteries and may not be easily detected by conventional angiography. Subclinical renal infarct also may occur despite patent renal angiography.

Computed tomography virtual intravascular endoscopy in the evaluation of fenestrated stent graft repair of abdominal aortic aneurysms

BACKGROUND

This study aimed to investigate the diagnostic value of computed tomography virtual intravascular endoscopy (VIE) in the follow-up of patients with abdominal aortic aneurysm (AAA) treated with fenestrated stent grafts.

METHODS

A total of 19 patients (17 males and 2 females; mean age: 75 years) with AAA undergoing fenestrated stent grafts were retrospectively studied. Pre- and post-fenestration computed tomography data were reconstructed for the generation of VIE images of aortic ostia and fenestrated stents and compared with two-dimensional axial and multiplanar reformation (MPR) images. Serum creatinine was measured pre and post fenestration to evaluate the renal function.

RESULTS

The mean intra-aortic length measured by VIE, two-dimensional axial and MPR were 4.7, 4.4 and 4.6 mm, respectively, for the right renal stent; 5.0, 4.9 and 5.0 mm, respectively, for the left renal stent; and 5.9, 6.0 and 6.0 mm, respectively, for the superior mesenteric artery stent. Comparisons of these measurements did not show significant difference (P > 0.05). The mean diameters of renal artery ostia measured on VIE visualization pre and post fenestration were 9.2 x 8.3 and 10 x 8.9 mm for the right renal ostium; 8.3 x 7.1 and 9.9 x 8.9 mm for the left renal ostium, with significant changes observed (P < 0.01). No renal dysfunction was observed in this group.

CONCLUSION

VIE is a valuable visualization tool in the follow-up of fenestrated stent graft repair of AAA by providing intraluminal appearance of fenestrated stents and measuring the length of stent protrusion.

Development of endovascular stent-grafts

The very first experiences in the early 1990s with endovascular aortic stent-grafts were associated with significant numbers of complications including an inability to deploy the stent-graft, conversion to open surgery, and aneurysm rupture. By the mid-1990s, improved home-made and commercially available stent-grafts started to appear. These devices could be successfully deployed in the aorta, achieving aneurysm exclusion with low morbidity and mortality. However, follow-up results raised concerns about the longer-term durability. Gradually, too, these problems have been addressed such that, in the recent UK multi-centre randomized controlled trial of endovascular versus open aneurysm repair, aneurysm-related mortality was 3 per cent less in the endovascular group four years following surgery. Currently the indications for aortic stent-grafts are being expanded. It is now possible to maintain perfusion successfully in aortic side branches and to treat aneurysms that would have once been thought untreatable. This review paper reviews the main developments in endovascular stent-grafting and the major role played by medical engineering and technology.

Comparison of renal function after endovascular aneurysm repair with different transrenally fixated endografts

OBJECTIVE

Transrenal fixation of abdominal aortic endografts may provide a more secure proximal attachment with few deleterious effects with respect to renal function. This study's purpose was to determine whether different metals used in two commercially available endografts (Cook Zenith and Medtronic Talent) result in different effects on renal function when placed across renal ostia.

METHODS

A total of 140 consecutive patients, between August 2003 and April 2005, who underwent elective endovascular repair of an aortic aneurysm with a nitinol or stainless steel-based endograft with transrenal fixation were reviewed with a mean follow-up period of 5.5 months (range, 1-22 months). The main outcome variable was the percentage change in creatinine clearance (CrCl), which was determined before surgery and at the most recent follow-up. Multiple regression analysis was performed to analyze the contribution of various factors to any deterioration in renal function.

RESULTS

The 140 patients were predominantly male (86%), with a mean age of 75 years (range, 56-92) and a mean aneurysm diameter of 62 mm (range, 42-110 mm). The mean intraoperative contrast use was 67 mL (range, 45-160 mL), and after surgery these patients received a mean of 3 surveillance computed tomographic scans (range, 1-7). Nineteen cases (13.6%) required deliberate accessory renal artery coverage. CrCl did not change significantly after surgery; the mean change in CrCl at the end of follow-up was a 2.5% decrease. There was no difference in the reduction in CrCl between endograft types. Only 14.3% of patients experienced a greater than 20% decrease in CrCl. Multiple regression analysis failed to show a relationship between change in renal function and age, sex, aneurysm diameter, infrarenal neck dimensions, endograft type, coverage of accessory renal arteries, intraoperative contrast volume, preoperative CrCl, and postoperative computed tomographic scans. Length of follow-up was an independent predictor (P = .04).

CONCLUSIONS

Transrenal endograft fixation results in little deterioration in renal function during intermediate follow-up. The few patients who do experience a decline in renal function do so independently of any features related to the initial endovascular repair, and there is no difference in renal deterioration between endografts with nitinol and stainless steel transrenal bare metal stents.

Renal interventions after abdominal aortic aneurysm repair using an aortic endograft with suprarenal fixation

BACKGROUND

Our aim was to determine whether suprarenal fixation in endografts compromises renal artery (RA) flow and whether subsequent RA intervention is precluded by the stent struts.

METHODS

Prospectively acquired data from 104 patients with endovascular aneurysm repair (EVAR) of an abdominal aortic aneurysm using the Zenith endograft (Cook, Inc., Bloomington, IN) were analyzed. The Zenith device uses a 26-mm, uncovered, barbed Z stent for suprarenal function.

RESULTS

No RA stenosis, occlusion, or infarction resulted from the suprarenal stent. In 3 of 104 (2.9%) patients, RA compromise (2 stenoses, 1 occlusion) was caused by impingement of graft material on the lowermost RA. The 2 RA stenoses were stented successfully at 1 and 7 months post-EVAR. Six of 104 (5.8%) patients developed late stenoses unrelated to the endograft: all were stented successfully from 19 to 36 months after EVAR. One patient with severe RA stenosis had balloon angioplasty pre-EVAR and then was stented electively 6 weeks post-EVAR.

CONCLUSIONS

Our data show that the suprarenal fixation of the Zenith aortic endograft does not cause RA stenosis, occlusion, or infarction, nor does it preclude post-EVAR renal artery intervention.

Transrenal Fixation of Aortic Stent-Grafts: Short- to Midterm Effects on Renal Function—A Systematic Review

PURPOSE

To perform a systematic review of the short- to midterm effects of transrenal fixation of aortic stent-grafts on renal function in patients with abdominal aortic aneurysms.

MATERIALS AND METHODS

A search of the PubMed, MEDLINE, and EMBASE databases for English-language literature was performed. Studies with at least 10 patients were included for data analysis. Only studies on transrenal fixation of aortic stent-grafts that included follow-up results for renal function were included. A log-linear model was used for meta-analysis to compare transrenal fixation with infrarenal fixation.

RESULTS

Twenty-two studies met the inclusion criteria. Because two studies analyzed the same group of patients, one was excluded, for a total of 21 studies. Comparisons between transrenal fixation and infrarenal fixation were found in seven studies. For transrenal versus infrarenal fixation, the combined odds ratio, 95% confidence interval, and P value were found to be statistically significant with respect to postprocedural renal infarction only (combined odds ratio, 5.189; 95% confidence interval: 3.198, 8.420; P < .001). No significant difference was found between transrenal and infrarenal fixation with respect to renal dysfunction, renal artery occlusion, or endoleaks (P > .05).

CONCLUSION

Transrenal fixation of aortic stent-grafts seems to be a relatively safe alternative compared with infrarenal fixation in terms of short- to midterm follow-up. Postprocedural renal infarction, however, was significantly higher for transrenal fixation.

Endovascular aneurysm repair with suprarenal vs infrarenal fixation: A study of renal effects

OBJECTIVES

Although suprarenal fixation may be of benefit during endovascular aneurysm repair (EVAR), its safety with regards to renal effects remains uncertain. To date, there has been no controlled study of the topic, with most reports relying upon single-center experiences that use heterogeneous patient populations and devices from different manufacturers. The purpose of this analysis was to evaluate the effect of suprarenal fixation on renal function by comparing homogeneous patient populations receiving EVAR grafts from a single manufacturer that are identical in design and delivery method, except for utilizing either suprarenal (SR) or infrarenal (IR) fixation.

METHODS

During two pivotal US Food and Drug Administration trials, 283 patients underwent EVAR with the Powerlink bifurcated graft. The trials' inclusion and exclusion criteria and grafts were identical except for fixation scheme. Clinical, laboratory, and computed tomographic (CT) data were retrospectively reviewed. A comparison of preoperative, perioperative (1 to 7 days), and postoperative (>7 days) alterations in serum creatinine (SCr), creatinine clearance (CrCl), and blood pressure was performed. Renal adverse events were determined by CT scan and clinical chart review and included renal infarction, renal artery stenosis (either progressive or requiring renal stent placement), and renal artery occlusion.

RESULTS

Both SR and IR groups demonstrated a significant increase in SCr and a decrease in CrCl over time. No significant difference in SCr or CrCl existed between groups during any time period. There were no differences in postoperative renal impairment (IR, 10.2%; SR, 7.6%, P = .634), the need for hemodialysis (IR, 0.7%; SR, 0%, P = 1.00), or systolic and diastolic blood pressure during subsequent follow-up between treatment groups. There was no significant difference in the number of renal adverse events detected by CT between the IR (10, 6.8%) and SR (3, 3.8%) groups (P = .550).

CONCLUSION

Suprarenal fixation does not lead to a significant increase in acute renal events, renal impairment, or alteration in blood pressure compared with infrarenal fixation. Patients undergoing aneurysm repair with devices that use either suprarenal or infrarenal fixation develop progressive renal dysfunction over time. Further studies are needed to determine the long-term effects of suprarenal fixation on renal function and progression of renal artery stenosis.

The impact of aortic endografts on renal function

OBJECTIVE

To determine the impact on late postoperative renal function of suprarenal and infrarenal fixation of endografts used to treat infrarenal abdominal aortic aneurysm (AAA).

METHODS

Retrospective analysis of 277 patients treated from 2000 to 2003 with three different endografts at two clinical centers. Five patients on dialysis for preoperative chronic renal failure were excluded. Group IF of 135 patients treated with an infrarenal device (Medtronic AneuRx) was compared with group SF of 137 patients treated with a suprarenal device (106 Cook Zenith and 31 Medtronic Talent). Renal function was evaluated by calculating preoperative and latest postoperative creatinine clearance (CrCl) using the Cockcroft formula. Patients who developed a >20% decrease in CrCl were considered to have significantly impaired renal function.

RESULTS

There were no significant differences in patient age, sex, aneurysm size, preoperative risk factors, dose of intra- and postoperative contrast, or baseline CrCl (IF: 69.3 mL/min, SF: 71.7 mL/min, P = .4). Follow-up time of 12.2 months was the same in both groups. CrCl decreased significantly during the follow-up period in both groups (IF: 69.3 mL/min to 61.7 mL/min, P < .01; SF: 71.7 mL/min to 64.9 mL/min, P < .03). Postoperative CrCl (IF: 61.7 mL/min, SF: 64.9 mL/min, P = .3), and the rate of CrCl decrease during the follow-up period (IF: -10.9%, SF: -9.5%, P = .2) was not different between the two groups. The number of patients with a >20% decrease in CrCl was not different between the two groups (IF: n = 35 [25.9%], SF: n = 41 [29.9%], P = .46). However, the magnitude of decrease in CrCl in patients with renal impairment was greater in patients treated with suprarenal fixation endografts (SF: -39%) compared with those treated with infrarenal endografts (IF: -31%, P = .005). This greater degree of renal impairment was not due to identifiable differences in preoperative risk factors, age, or baseline CrCl. No patients in these series required dialysis.

CONCLUSIONS

Regardless the type of endograft used, there is a 10% decrease in CrCl in the first year after endovascular aneurysm repair. Suprarenal fixation does not seem to increase the likelihood of postoperative renal impairment. Decline in renal function over time after endovascular aortic repair is probably due to multiple factors, and measures known to be effective in protecting kidneys should be considered for these patients. Long-term follow-up with measurement of CrCl, along with renal imaging and regular blood pressure measurements, should be performed to detect possible late renal dysfunction. Prospective studies comparing suprarenal versus infrarenal fixation are needed to confirm those results.

Single Center Experience with a New Commercially Available Thoracic Endovascular Graft

PURPOSE

To evaluate the intra-operative performance and clinical outcome of a new commercially available stent-graft for the treatment of thoracic aortic diseases.

METHODS AND PATIENTS

From January 2003 to October 2004, 45 consecutive patients received endovascular treatment with the Zenith TX1 device for diseases of the thoracic aorta at a single center in northern Italy. Indications included disease of the descending thoracic aorta in 26 cases, of the aortic arch in 17 cases and of the thoraco-abdominal aorta in two cases. We treated 38 atherosclerotic aneurysms, two post-traumatic aortic ruptures, two penetrating ulcers, two chronic dissections and one case was treated for aortic bleeding after voluntary acid ingestion for attempted suicide. General anesthesia was used in 20 cases. Combined or hybrid endovascular and open surgical repair was performed in 11 patients. Mean follow-up was 7 months (range 1-22 months).

RESULTS

Technical success was obtained in 44 patients (98%). One primary type I endoleak occurred (2%). ICU was used in 12 cases with a mean stay of 1 day. The mean hospital stay was 6 days (range 4-13 days). There were no hospital deaths or strokes but one transient paraplegia (2%). A type II endoleak was observed in one case and resolved spontaneously 1 month later. No aneurysm enlargement, endograft migration or structural failures were observed during follow-up. Two late unrelated-deaths were observed.

CONCLUSIONS

This stent-graft does not fulfill all the characteristics of the ideal graft, however, it proved to be safe and allowed satisfactory short term results in this group of patients treated at a single center.

Incidence of Renal Infarctions After Transrenal Stent Placement in an Animal Model

PURPOSE

To evaluate the incidence and appearance of renal infarctions after transrenal stent placement in an animal model.

METHODS

An aortic stent was placed via a femoral approach in 20 female Merino sheep. Ten animals had intentional coverage of one renal ostium with the bare struts, 1 sheep had both renal artery ostia covered, and the other 9 sheep had no stent impingement on the renal orifices. Animals were sacrificed after 3 to 12 months (mean 6) for gross pathological and histological evaluation. Infarction locations and patterns were evaluated and correlated to stent placement.

RESULTS

Of the 40 renal arteries, coverage was proven at autopsy in 12 cases; the remaining 28 arteries were free of any stent overlay. Overall, 14 (35%) renal infarctions were detected; 7 were found in the 12 arteries with a transrenal stent (58.3% incidence in covered renal arteries). By comparison, the other 7 infarctions were found in the 28 unaffected arteries (25% incidence in noncovered renal arteries; p = 0.04). All infarctions appeared to be well-defined punctate lesions.

CONCLUSIONS

A transrenal stent position in the abdominal aorta is related to increased renal infarctions in an animal model.

Transrenal fixation of aortic stent-grafts: current status and future directions

Aortic stent-graft repair has been widely used in clinical practice for more than a decade, achieving satisfactory results compared to open surgical techniques. Transrenal fixation of stent-grafts is designed to obtain secure fixation of the proximal end of the stent-graft to avoid graft migration and to prevent type I endoleak. Unlike infrarenal deployment of stent-grafts, transrenal fixation takes advantage of the relative stability of the suprarenal aorta as a landing zone for the uncovered struts of the proximal stent. These transostial wires have sparked concern about the patency of the renal arteries, interference with renal blood flow, and effects on renal function. Although short to midterm results with suprarenal stent-grafts have not shown significant changes in renal function, long-term effects of this technique are still not fully understood. This review will explore the current status of transrenal fixation of aortic stent-grafts, potential risks of stent struts relative to the renal ostium, alternative methods to preserve blood flow to the renal arteries, and future directions or developments in stent-graft design to prevent myointimal proliferation around the stent struts.

Effect of Suprarenal Stent Struts on the Renal Artery with Ostial Calcification Observed on CT Virtual Intravascular Endoscopy

OBJECTIVES

The behaviour of stent struts crossing the renal ostia and their effect on renal ostia configuration is not well understood. The study aims to investigate whether suprarenal stent struts affect the morphological change of the renal artery with ostial calcification observed on CT virtual intravascular endoscopy.

METHODS

Nine patients with abdominal aortic aneurysms undergoing suprarenal fixation of stent grafts were included in the study. All patients received a Zenith endovascular graft with uncovered suprarenal components placed above the renal arteries. Renal ostial calcification and configuration of stent wires crossing the renal ostium were characterized in each patient and maximal transverse and longitudinal diameters of the renal ostia were measured on virtual endoscopy pre- and post-stent grafting.

RESULTS

There were altogether 17 renal ostia assessed with one patient having atrophic left kidney and no renal ostium being observed. Ostial calcification was found in five of the left renal ostia and five of the right renal ostia with one patient having bilateral ostial calcification. There was no significant difference between the renal ostial diameters measured pre- and post-stent grafting (p>0.05). Suprarenal stent struts were found to cross the renal ostia in various configurations observed on virtual endoscopy. All of the renal arteries were patent on follow-up CT scans after suprarenal fixation without stenosis or occlusion being observed. One patient with atrophic left renal artery developed renal failure following suprarenal stent grafting and received renal dialysis, while in the remaining cases median serum creatinine level did not change significantly.

CONCLUSIONS

Suprarenal stent struts did not significantly affect the renal ostia with ostial calcification in terms of the diameter measurements and renal function. Further studies deserve to investigate the long-term effect of stent struts on the renal artery in terms of cross-sectional area reduction caused by stent wires and ostial calcification.

Treatment of short-necked infrarenal aortic aneurysms with fenestrated stent-grafts: short-term results

INTRODUCTION

A proximal neck of 15 mm length is usually required to allow endovascular repair of abdominal aortic aneurysms (EVAR). Many patients have been refused EVAR due to a short neck. By customising fenestrated grafts to the patients' anatomy, we can offer an endovascular solution, especially for patients who are unsuitable for open repair.

METHODS

Eighteen patients were selected for fenestrated stent-grafting if they presented with an abdominal aneurysm of at least 55 mm in diameter, a short neck (less than 15 mm), plus contra-indications for open repair (cardiopulmonary impairment or a hostile abdomen). The stent-graft used was a customised fenestrated model based on the Cook Zenith composite system. We used additional stents to ensure apposition of the fenestrations with the side branches.

RESULTS

All endovascular procedures were successful. Out of the 46 targeted side branches (10 superior mesenteric arteries, 36 renal arteries), 45 were patent at the end of the procedure. One accessory renal artery became occluded by the stent-graft. There was one possible proximal type I endoleak, which later proved to be a type II endoleak. There was no mortality, but complications occurred in six patients: two cardiac complications, three urinary complications and one occlusion of a renal artery. At follow-up (mean 9.4 months, range 1-18), there were no additional renal complications and all the remaining targeted vessels stayed patent.

DISCUSSION

By customizing fenestrated stent-grafts, it is possible to position the first covered stent completely inside the proximal neck, thus achieving a more stable position. The additional side-stents may also contribute to a better fixation. This technique may become a valuable alternative for patients who are at high risk from open surgery.

Diagnostic value of CT virtual intravascular endoscopy in aortic stent-grafting

PURPOSE

To investigate the diagnostic value of postprocessing techniques for 3-dimensional (3D) computed tomography (CT), with emphasis on CT virtual intravascular endoscopy (VIE), in patients with abdominal aortic aneurysms (AAA) treated with suprarenal stent-grafts.

METHODS

The preprocedural and postprocedural CT datasets from 47 AAA patients (40 men; mean age 75 years, range 61-87) undergoing aortic stent-grafting with suprarenal fixation were examined. The CT datasets were processed to create various 3D reconstructions: shaded surface display (SSD), maximum intensity projection (MIP), and VIE. Three independent radiologists assessed various diagnostic parameters for each 3D reconstruction method and compared them to axial CT images.

RESULTS

Scores for VIE reconstructions were inferior to axial CT images in the visualization of normal arterial branches, measurement of the aneurysm diameter and neck length, as well as assessment of vessel patency and presence of endoleaks. VIE was rated superior to axial CT and other 3D imaging methods in visualizing the configuration of stent struts relative to the aortic branch ostia and the number of stent wires crossing the ostia in >80% of cases.

CONCLUSIONS

VIE was not found to play a role in most preoperative situations compared to axial CT images. However, VIE provided additional postgrafting information on the 3D relationship of the suprarenal stent struts to the aortic branch ostia (in particular the renal and superior mesenteric arteries). VIE findings might aid clinicians in accurately assessing the effect of suprarenal stent-grafting on the renal arteries.

Relationship of proximal fixation to postoperative renal dysfunction in patients with normal serum creatinine concentration

OBJECTIVES

This study was performed to determine whether there is deterioration in renal function during follow-up in patients who have undergone endovascular aneurysm repair (EVAR), as recommended by the device manufacturers; to determine whether suprarenal fixation correlates with impairment of renal function; and to explore the potential implication of life-long surveillance of renal function with contrast-enhanced computed tomography.

METHODS

One hundred forty-six consecutive patients underwent EVAR at our institution. Data from 113 of these patients who were free from preoperative renal insufficiency or postoperative renal disease were analyzed. Fifty-three patients received infrarenal (IR) fixation devices, and 60 patients received suprarenal (SR) fixation devices. All SR fixation devices were placed under investigational device exemption protocols. The average follow-up was 688 days. Sixty-five consecutive patients who had undergone open repair of an abdominal aortic aneurysm (AAA) served as the control group.

RESULTS

Preoperative creatinine concentration, intraoperative blood loss, contrast volume, and number of contrast-enhanced procedures were not significantly different between the IR and SR groups. Two renal artery occlusions (1 SR, 1 IR; P=NS) were identified, and 8 renal infarcts (5 SR, 3 IR; P=NS). There was an increase in mean creatinine concentration in the open AAA, IR, and SR fixation groups at each time point in the analysis. Mean elevation in creatinine concentration at 12, 24, and 36 months was 0.10, 0.10, and 0.04 mg/dL, respectively, for open AAA repair; 0.20, 0.21, and 0.28 mg/dL for IR fixation; and 0.15, 0.21, and 0.12 mg/dL for SR fixation. At life table analysis, renal impairment at 36 months was seen in 36% +/- 9% of patients in the IR group, 25% +/- % of patients in the SR group, and 19% +/- 6% of patients in the open AAA group (P=.04 for IR fixation vs open AAA repair).

CONCLUSIONS

A decrease in kidney function is seen after EVAR, regardless of fixation level, that is independent of renal disease and renal arterial occlusion. In patients with normal renal function the site of proximal fixation does not affect postoperative creatinine concentration. The decrease in renal function is likely related to the repetitive administration of contrast agent.

A UK Multi-centre Experience with a Second-generation Endovascular Stent-graft: Results from the Zenith Users Group

BACKGROUND

Endovascular aneurysm repair has been criticised for high rates of technical failure and secondary intervention. Second generation stent-grafts have been developed in an attempt to reduce these problems. The results of a UK multi-centre experience with a second generation device (Zenith) are presented.

METHODS

Data were collected retrospectively from five experienced UK vascular centres in patients undergoing endovascular aneurysm repair with the Zenith stent-graft.

RESULTS

A total of 269 patients underwent attempted aneurysm repair with the Zenith device. Median aneurysm diameter was 65 (interquartile range 52-78) mm. There were no conversions to open repair. Peri-operative mortality was 4.1% (11/269). On the initial post-operative scan, 94.1% of aneurysms were successfully excluded. During a median follow-up of 363 (interquartile range 154-720) days there were 19 secondary interventions and two aneurysm ruptures.

CONCLUSIONS

Second generation endovascular stent-graft designs such as the Zenith are associated with low rates of intra-operative technical complications. Few secondary interventions have been necessary during follow-up; however, surveillance is essential to ensure they continue to perform.

Effect of suprarenal versus infrarenal aortic endograft fixation on renal function and renal artery patency: a comparative study with intermediate follow-up

PURPOSE

Suprarenal fixation of aortic endografts appears to be a safe option in patients with a short or conical proximal aortic neck. However, concern persists regarding the long-term effect on renal function when renal artery ostia are crossed by the uncovered stent. We investigated the effect of suprarenal versus infrarenal endograft fixation on renal function and renal artery patency after endovascular aortic aneurysm repair.

METHODS

Records of 91 patients who underwent endovascular aortic aneurysm repair with a modular bifurcated stent graft between November 1999 and January 2002 were reviewed retrospectively. Two patients receiving dialysis because of chronic renal failure were excluded. Infrarenal fixation was used in 57 patients (group 1), and suprarenal fixation was used in 32 patients (group 2). In two patients in group 1 a Gianturco Z stent was inserted transrenally because of intraoperative proximal type I endoleak, and data for these patients were excluded from analysis. Follow-up evaluation was performed at 1, 6, and 12 months, and yearly thereafter, and included clinical assessment, measurement of serum creatinine concentration (SCr), and computed tomography angiography, per standard protocol. Median follow-up was 12 months (range, 1-36 months).

RESULTS

There was no statistically significant difference in patient demographic data, aneurysm size, or preoperative risk factors. Median SCr was significantly higher in group 2 (suprarenal fixation) than in group 1 (infrarenal fixation) preoperatively (1.2 mg/dL [range, 0.6-2.3 mg/dL] vs 0.9 mg/dL [range, 0.6-1.9 mg/dL], P =.008) and at 1 month postoperatively (1.1 mg/dL [range, 0.8-5.6 mg/dL] vs 1.0 mg/dL [range, 0.6-2.1 mg/dL], P =.045). There was a significant increase in median SCr in both groups at 1 month postoperatively (group 1, 1.0 mg/dL [range, 0.6-2.1 mg/dL], P =.05; group 2, 1.1 mg/dL [range, 0.8-5.6 mg/dL] [mean SCr, 1.35 mg/dL vs 1.15 mg/dL, respectively], P <.05). In group 1 SCr was increased significantly at 6 and 12 months (P <.001), whereas in group 2 SCr also increased at 6 and 12 months, but not significantly. The change in SCr over time was not significantly different between the two groups. In two of 32 patients in group 2, renal artery occlusion developed, associated with perfusion defects in renal parenchyma and persistently elevated SCr. Analysis of renal artery patency did not demonstrate any association between patency and treatment. No patient developed hypertension during follow-up.

CONCLUSIONS

Suprarenal endograft fixation does not lead to significant renal dysfunction, and renal artery occlusion is uncommon within 12 months. A larger study with longer follow-up is essential to determine overall effects on renal function and renal artery patency.

Long-term renal function following endovascular aneurysm repair with infrarenal and suprarenal aortic stent-grafts

PURPOSE

To determine in a retrospective analysis the incidence of renal impairment (RI) following endovascular repair (EVR) of abdominal aortic aneurysm (AAA), to assess the morbidity and mortality in endograft patients with preoperative RI, and to examine the impact of suprarenal stent-grafts on renal function.

METHODS

From March 1994 to October 2001, 315 AAA patients (289 men; mean age 72.4+/-7.0 years) undergoing EVR were entered prospectively into a vascular registry. The patients received either an in-house custom-made stent-graft or one of several commercially made devices implanted with infrarenal or suprarenal fixation. Renal function was monitored by serum creatinine measurements prior to discharge and at 3, 6, and 12 months and annually thereafter. Preoperative RI was defined as a serum creatinine >130 micro mol/L and/or long-term dialysis. Postoperative RI referred to a >20% increase in the serum creatinine over baseline. Additional deterioration of renal function in patients with preoperative RI was referred to as postoperatively worsened RI.

RESULTS

Of the 315 patients treated, 220 (69.8%) were considered high risk (ruptured AAA or ASA grade III or IV). Sixty-nine (21.9%) patients had preoperative RI (6 [1.9%] on preoperative dialysis). A suprarenal stent-graft was used in 169 (53.7%) patients and infrarenal stent-graft in the remaining 146 (46.3%). The mean follow-up was 30.1+/-22.7 months. Postoperative RI occurred in 53 (16.8%) patients (24 [7.6%] transient, 29 [9.2%] persistent). Patients with preoperative RI had a significantly higher incidence of postoperatively worsened RI (37.7% versus 11.0%, p<0.0001) and a higher mortality related to RI (7.2% versus 1.6%, p=0.02). Suprarenal fixation had no influence on the incidence of RI, on perioperative mortality, or on mortality related to RI. The only significant predictive factor of postoperative RI was preoperative RI (risk ratio 5.09, 95% CI 2.38 to 10.87, p=0.0001).

CONCLUSIONS

Endovascular AAA repair may lead to persistent postoperative RI in nearly 10% of cases, especially in patients with preoperative RI. Suprarenal stent-graft fixation does not seem to have any deleterious effect on renal function. Further long-term studies are required to confirm the innocuous nature of transrenal stent placement.

Multiple stenting in Takayasu arteritis

PURPOSE

To illustrate the possible peri- and postprocedural complications of stent treatment for Takayasu arteritis and suggest ways of reducing these risks.

CASE REPORT

A 69-year-old woman with Takayasu arteritis had multiple stents implanted in the aortic arch (3 Memotherm) and main branches of the thoracic aorta (individual Corinthian stents in the subclavian and brachiocephalic arteries) following balloon dilation. She suffered reperfusion injury with cerebral hemorrhage following the procedure, preventing the use of anticoagulation or antiplatelet therapy. Further cerebral infarctions/hemorrhages over the ensuing months led to her death.

CONCLUSIONS

Severe vascular disease of any cause confers a poor prognosis. Endovascular stenting may seem an attractive option for management of these patients, but there is often significant morbidity and mortality associated with the underlying disease as well as the stent.

Renal function after aortic stent-grafting including coverage of renal arterial ostia

Considerable experience has been gained with endoluminal stent-graft techniques for the treatment of infrarenal aortic aneurysms. The inclusion of uncovered suprarenal stents eases the treatment of cases with a short, angulated, or bottlenecked proximal neck. However, few data have been published on the effect of a stent-graft crossing renal artery ostia on long-term renal function. We therefore retrospectively analyzed the influence of intra-aortic stent-grafts, including suprarenal fixation on long-term renal function. Thirty-nine patients who received a Gianturco Z stent across renal artery ostia as part of a made-to-measure stent-graft treating an infrarenal aortic aneurysm were evaluated at 6 (all patients) and 30 months (15 patients) after surgery. Renal function evaluation included serum creatinine level, creatinine clearance using the Cockcroft-Gault formula, and renal tomography. Initial technical success was achieved in all patients. There were no minor or major complications. Mean serum creatinine levels were 1.16 +/- 0.25, 1.12 +/- 0.28, and 1.24 +/- 0.25 mg/dL before and 6 and 30 months after endoluminal stent-graft performance, respectively (P = not significant [NS]). Mean creatinine clearances were 60.3 +/- 19.7, 63 +/- 23, and 60.6 +/- 17.5 mL/min before and 6 and 30 months after endoluminal stent-graft performance, respectively (P = NS). Only two patients (5%) had a decrease in glomerular filtration rate greater than 20% at 6 months. Both patients had renal insufficiency before endovascular grafting. Renal function was stable in all patients at 30 months' follow-up. We suggest that renal function is unaffected by coverage of renal arterial ostia with Gianturco Z stents.

Renal infarction following endovascular aortic aneurysm repair: incidence and clinical consequences

PURPOSE

To investigate the incidence of renal infarction following endovascular abdominal aortic aneurysm (AAA) repair, with particular emphasis on a comparison of suprarenal versus infrarenal endograft placement.

METHODS

Ninety-nine patients (92 men; average age 68 years) who had undergone endovascular AAA repair between July 1995 and July 1999 and who had at least 12 months' follow-up were studied with spiral computed tomographic scans to identify suprarenal endograft deployment and renal infarction.

RESULTS

Among the 193 renal arteries available for study, partial or complete transrenal endograft placement was found in 69 (36%). Sixteen (8.3%) renal infarctions were identified by the postoperative imaging studies. Perfusion of these kidneys was supplied by 6 (8.7%) of the 69 overstented renal arteries and 7 (5.6%) of the 124 uncovered arteries (p > 0.05). In the 3 other cases, intentional accessory renal artery occlusion by the stent-graft fabric led to frank segmental renal infarctions, which were visualized as territorial-perfusion defects affecting up to 27% of the renal volume. In the other 13 infarcted kidneys, the punctate deficits involved <10% of the parenchymal volume. Renal retention values were unaffected in 15 (94%) of 16 patients.

CONCLUSIONS

Documented renal infarctions following endovascular aortic stent-graft placement are not common and do not appear to be associated with suprarenal endograft fixation.

Intrarenal color duplex examination of aortic endograft patients with suprarenal stents

PURPOSE

To report an experience using intrarenal color duplex ultrasonography (ICDU) to detect high-grade renal artery stenosis in patients who had endovascular repair of abdominal aortic aneurysm (AAA) with suprarenal stent fixation.

METHODS

Twenty-eight patients (25 men; mean age 71 years, range 58-83) who had endovascular AAA repair with suprarenal stenting at least 3 months prior to commencement of this study were screened with ICDU. Acceleration time (AT), peak systolic velocity (PSV), end diastolic velocity (EDV), and resistive index (RI) were measured. The Doppler waveform was quantitatively scored on a scale from 0 to 4. AT >0.07 seconds, RI <0.45, or a Doppler waveform score of 0 or 1 (indicating loss of early systolic peak) were indicative of high-grade renal artery stenosis.

RESULTS

Median follow-up was 15.5 months (range 3-34). ICDU was successful in 54 (98%) of 55 kidneys scanned. No AT values exceeded 0.07 seconds, all RIs were >0.45, and no waveforms had loss of early systolic peak, indicating that no patient had evidence of high-grade renal artery stenosis.

CONCLUSIONS

ICDU is a simple and affordable method that seems well suited to periodic screening in patients with suprarenal stents. Longer follow-up with a larger number of patients is needed before definite conclusions can be drawn about the effect of suprarenal stenting on renal circulation.

Nitinol - its use in vascular surgery and other applications

OBJECTIVES

to describe the physical properties of shape-memory alloys and the surgical, scientific and commercial applications of nitinol, in particular.

DESIGN AND METHODS

a Medline, Internet and library search with contributions from commerce to describe the alloy's structure, behaviour and biocompatibility, and design for devices constructed from nitinol.

RESULTS

nitinol has the properties of thermal shape memory and superelasticity that make it ideal for many vascular and general surgical prostheses and disposables, and for various commercial applications.

CONCLUSIONS

further research into shape-memory alloys from scientific and commercial groups should widen their use in vascular and endovascular surgery.

Placement of a fenestrated Palmaz stent across the renal arteries. Feasibility and outcome in an animal study

OBJECTIVES

To investigate the feasibility of placing stents across renal arteries. Design we have studied in pigs: (i) the feasibility of accurately placing a fenestrated stent in front of one renal ostium; (ii) the short-term effects on renal arteries and function after the placement of such a fenestrated stent.

MATERIALS AND METHODS

Eight fenestrated Palmaz stents were placed over pigs' renal ostia under fluoroscopy. Five weeks later, angiograms were performed and the animals were sacrificed. Proliferation of the healing tissues over the ostia was measured and analysed by microscopy. Serum creatinine was measured prior to all angiograms and at 5 weeks.

RESULTS

All eight stents were correctly placed. One stent later migrated and was excluded from the study. One pig died at day 1. Gross examination confirmed the correct placement of the fenestrations in four pigs out of seven (57%). In the six remaining pigs, at 5 weeks, there was no angiographic evidence of stent misplacement and all the kidneys were fully perfused. Nine renal ostia were covered by struts and neointima with a mean area of coverage of 38+/-5% altogether. No tissue proliferation was observed over the three renal ostia located in front of the fenestration. Serum creatinine did not significantly increase at 5 weeks.

CONCLUSION

Creating a fenestration in a stent for renal arteries may be worth while in order to avoid neointimal covering of the renal ostia. However, accurate placement of such a fenestrated stent remains a difficult task.