Early Feasibility of Endovascular Repair of Distal Aortic Arch Aneurysms Using Patient-Specific Single Retrograde Left Subclavian Artery Branch Stent Graft.

OBJECTIVE: To describe the feasibility and outcomes of endovascular repair of distal aortic arch aneurysms using a patient-specific stent graft with a pre-loaded single retrograde left subclavian artery (LSA) branch stent graft. METHODS: We reviewed the clinical data and outcomes of consecutive patients enrolled in an ongoing prospective, non-randomized physician-sponsored investigational device exemption study to evaluate the outcomes of endovascular aortic arch repair using patient-specific arch branch stent grafts (William Cook Europe, Bjaeverskov, Denmark) between 2019 and 2022. All patients received a design with triple-wide scallop and a single retrograde LSA branch with a pre-loaded catheter. RESULTS: There were five male patients with median age of 77 years old (72-80) treated using the single LSA branch stent graft. Technical success was achieved in all patients. Median operating time, fluoroscopy time, and total radiation dose area product were 103 (78-134) minutes, 26 (19-39) minutes, and 123 (71-270) mGy.cm2, respectively. There were no 30-day or in-hospital mortality, neurological or other major adverse events (MAEs). During median follow-up of 21 (20-27) months, all patients were alive with patent LSA branches, except for one who died of COVID-19 complications. There was no branch instability or secondary interventions. CONCLUSION: This early feasibility study demonstrates successful endovascular repair of distal aortic arch aneurysms using a patient-specific stent graft with single retrograde LSA branch without technical failures, mortality or neurological events. Larger clinical experience and longer follow-up are needed to determined effectiveness of this approach in patients who need endovascular repair with proximal extension into Zone 2.

Multicenter global early feasibility study to evaluate total endovascular arch repair using three-vessel inner branch stent-grafts for aneurysms and dissections.

OBJECTIVE: We evaluated the outcomes of total endovascular aortic arch repair using three-vessel inner branch stent-grafts for aneurysms and chronic dissections. METHODS: We reviewed the clinical data and outcomes of consecutive patients treated by total endovascular aortic arch repair at eight academic centers using three-vessel inner branch stent-grafts (William Cook Europe, Bjaeverskov, Denmark) from 2016 to 2019. All patients received three-vessel designs with two antegrade and one retrograde inner branch, which was used to incorporate the innominate, left common carotid, and left subclavian arteries. The antegrade inner branches were accessed via a carotid or an upper extremity approach. A preloaded catheter was used for access to the retrograde left subclavian artery branch via a transfemoral approach. The endpoints were technical success, mortality, major adverse events, any stroke (minor or major) or transient ischemia attack, secondary interventions, target vessel patency, target vessel instability, aneurysm-related mortality, and patient survival. RESULTS: A total of 39 patients (31 men [79%]; mean age, 70 ± 7 years) had undergone treatment of 14 degenerative (36%) and 25 chronic (64%) postdissection arch aneurysms. The clinical characteristics included American Society of Anesthesiologists class ≥III in 28 patients (95%) and previous median sternotomy for ascending aortic repair in 28 patients (72%). The technical success rate was 100%. Two patients had died in-hospital or within 30 days (5%), and two patients had experienced a stroke (one minor). The combined mortality and any stroke rate was 8% (n = 3). Major adverse events occurred in 10 patients (26%), including respiratory failure in 4 (10%) and estimated blood loss >1 L, myocardial infarction, and acute kidney injury in 2 patients each (5%). The median follow-up was 3.2 months (interquartile range, 1-14 months). Of the 39 patients, 12 (31%) required secondary interventions to treat vascular access complications in 5, endoleak in 6 (three type II, one type Ic, one type Ia/Ib, one type IIIa), and target vessel stenosis in 1 patient. At 1 year, the primary and secondary patency rates and freedom from target vessel instability were 95% ± 5%, 100%, and 91% ± 5%, respectively. Freedom from aortic-related mortality and patient survival was 94% ± 4% and 90% ± 6%, respectively. CONCLUSIONS: The findings from the present multicenter global experience have demonstrated the technical feasibility and safety of total endovascular aortic arch repair for aneurysms and chronic dissections using three-vessel inner branch stent-grafts. The mortality and stroke rates compare favorably with those after open surgical repair in a higher risk group of patients. However, the rate of secondary interventions was high (31%), emphasizing need for greater experience and longer follow-up.

Effect of proximal fixation length on complications after endovascular repair of type B aortic dissection.

OBJECTIVE: We evaluated the effect of the achieved proximal seal length on the outcomes after endovascular repair of acute type B aortic dissection (aTBAD). METHODS: A post hoc analysis was performed using data from two prospective, multicenter investigational studies of the Zenith Dissection Endovascular System (STABLE I and II). Patients treated for aTBAD within 14 days of symptom onset were included if complete preoperative and postoperative imaging data were available for review. The patients were divided into four groups according to the length of the achieved proximal seal according to the centerline imaging findings: ≥20 mm, ≥10 to <20 mm, ≥0 to <10 mm, and <0 mm. The outcomes stratified by the achieved proximal seal length were evaluated. All imaging findings were based on core laboratory analysis. RESULTS: A total of 110 patients were included in the present analysis; 51 were from STABLE I and 59 from STABLE II. Although the study protocol criteria required a ≥20 mm length of nondissected aorta distal to the left common carotid artery to serve as a proximal seal zone, an achieved proximal seal length of ≥20 mm was observed in only 19 of the 110 patients (17.3%) according to the location of stent-graft placement. After a mean follow-up duration of 41.6 ± 21 months, the cumulative rate of the composite device outcome (ie, proximal entry flow, retrograde dissection, transaortic growth, and stent-graft migration) was lowest in patients with an achieved proximal seal length of ≥20 mm (15.8%; 3 of 19). The cumulative rate increased as the seal length decreased (32.0% [8 of 25], 55.6% [20 of 36], and 60.0% [18 of 30] with a proximal seal length of ≥10 to <20 mm, ≥0 to <10 mm, and <0 mm, respectively; P < .01, Cochran-Armitage trend test). CONCLUSIONS: A clear inverse relationship was found between the proximal seal length achieved and associated adverse outcomes. This finding underscores the importance of landing the stent-graft in healthy, nondissected aorta to minimize the risk of complications and provide a durable repair in patients with aTBAD.

Applicability of a standardized thoracic endograft with a single branch for the left subclavian artery to treat aortic disease involving the distal arch.

OBJECTIVE: Coverage of the left subclavian artery (LSA) origin during thoracic endovascular aortic repair (TEVAR) is associated with increased neurologic complications. Our group is involved in the development of an off-the-shelf (OTS) thoracic endograft incorporating a left common carotid artery (LCCA) scallop and a retrograde inner branch for LSA perfusion. This study aimed to evaluate the arch morphology of patients treated by TEVAR and requiring LSA coverage to determine the applicability of this OTS device. METHODS: The preoperative anatomy of consecutive patients from three separate cohorts treated with TEVAR with LSA coverage was studied. High-quality preoperative computed tomography angiography images were analyzed on an imaging workstation. Location of the origin of the supra-aortic trunks and their anatomic relationship were depicted in all patients; the LCCA origin was set as reference point. We determined the proportion of arch morphology in our cohort of patients eligible for this OTS device configuration. RESULTS: There were 196 patients included in this study, 132 in the dissection cohort and 64 in the aneurysm cohort. The median length from the lower margin of the LCCA to the proximal aspect of the pathologic process was 25.0 mm (18.2-35.2 mm), with 68.4% (n = 134) of our cohort presenting with a proximal sealing zone length >20 mm. The median LCCA-LSA distance was 20.8 mm (16.6-25.4 mm). The median clock position of the LSA from the LCCA was -10 minutes (-30 to 0 minutes). In total, 127 patients (64.8%) could have been treated with the current OTS branched TEVAR configuration; 59 were excluded for proximal neck length distal to the LCCA <20 mm and 10 because of the clock position of the LCCA, and 9 first required a vertebral artery transposition. CONCLUSIONS: The low variability of LSA and LCCA locations in patients with distal aortic arch disease offers wide applicability of a new standardized thoracic branched endograft.

Off-the-shelf multibranched endograft for total endovascular repair of the aortic arch.

OBJECTIVE: The goal of this study was to select branched endograft designs that could fit most aortic arch anatomies. Such off-the-shelf endografts, once available, would be an endovascular therapeutic option to consider in the acute setting and would shorten the design and manufacturing process. METHODS: We retrospectively analyzed the endograft plans of all custom-made aortic arch branched endografts implanted between 2013 and early 2018 provided by the Cook Planning Center (EMEA Planning Services; Cook Medical, London, United Kingdom). Available data points of the endograft plans include proximal, intermediate, and distal endograft diameters; number of sealing stents; total length of the endograft; and number of branches. RESULTS: There were 286 two-branch endografts analyzed. We divided the endografts in three groups according to their proximal diameters: 34 mm, 36 mm, and 38 mm (group 1); 40 mm and 42 mm (group 2); and 44 mm and 46 mm (group 3). In group 1, 63% of the endografts had one proximal sealing stent, whereas in group 3, 63% had two proximal sealing stents. The distal diameters of the endografts ranged from 26 mm to 46 mm. The mean length was 236 mm (186-256 mm). A shorter standardized length of 211 mm was selected to anticipate distal extensions. According to our analysis, most group 1 patients could have been treated with a 38-mm proximal diameter and 30-mm distal diameter endograft with one sealing stent; most group 2 patients, with a 42-mm proximal diameter and 32-mm distal diameter endograft with both one and two proximal sealing stents; and most group 3 patients, with a 46-mm proximal diameter and 36-mm distal diameter endograft, also with both one and two proximal sealing stents. CONCLUSIONS: Five standardized off-the-shelf endografts can cover a majority of aortic arch anatomies and offer an option for acute endovascular treatment of aortic arch disease.

Applicability of the Zenith Inner Branched Arch Endograft.

Purpose: To evaluate the clinical and anatomical features of patients with arch pathology to better understand the applicability of the Zenith inner branched arch endograft (IBAE). Materials and Methods: A retrospective review was performed of 60 consecutive patients (mean age 62.5 years; 42 men) who presented with nonruptured aortic arch pathology at a single institution between 2009 and 2016. Patients were stratified into standard (no previous cardiac surgery, <80 years old, and no significant medical comorbidity), high (previous cardiac surgery or significant comorbidity), or prohibitive risk (turned down for operative intervention) for operative intervention. Anatomical measurements of the aorta were obtained on computed tomography scans; anatomical suitability was based on the device's instructions for use. Results: Overall, 27 (45%) patients had anatomy amenable to treatment with the existing IBAE. Inadequate proximal seal length and large ascending aortic diameters were the primary reasons for anatomical unsuitability. Shortening the inner curve seal zone from 25 to 15 mm and increasing the proximal seal zone diameter from 38 to 42 mm increased anatomical suitability to include 49 (82%) patients. Of these, 31 were in the high-risk cohort and 7 were deemed prohibitive risk; therefore, IBAE would have been strongly considered in these 38 patients. Conclusion: Based on anatomical criteria alone, nearly half of patients with aortic arch pathology have anatomy suitable to the Zenith IBAE in its current design. Arch branch vessel anatomy was not a limitation of the device. From a clinical standpoint, if endovascular repair were reserved for those at high or prohibitive risk for open repair, approximately 30% of patients would likely benefit from the IBAE in its current form.

Outcomes of a novel upper extremity preloaded delivery system for fenestrated-branched endovascular repair of thoracoabdominal aneurysms.

OBJECTIVE: The aim of this study was to evaluate the feasibility and outcomes of endovascular repair of thoracoabdominal aortic aneurysms (TAAAs) using a novel low profile (LP) device with upper extremity preloaded guidewire system (PGS) and compare procedural metrics and outcomes with a standard multibranch stent graft (t-Branch; Cook Medical, Bloomington, Ind). METHODS: We reviewed the clinical data of 232 consecutive patients treated by fenestrated-branched endovascular aortic repair for TAAA and enrolled in a prospective nonrandomized trial between 2014 and 2017. Patients who had repair using t-Branch or patient-specific TAAA devices using upper extremity LP-PGS were included. End points were technical success, operative and fluoroscopic time, patient radiation exposure, time from arterial access to complete device deployment, total contrast volume, and 30-day rates of major adverse events (MAEs) and mortality. RESULTS: There were 54 patients, including 33 males (67%) and 21 females (33%), with a mean age of 73 ± 9 years old. Forty-nine patients (91%) had extent I-III and five patients (9%) had extent IV TAAAs. Device design was t-Branch in 24 patients (44%) and LP-PGS in 30 patients (56%). A total of 206 renal-mesenteric arteries were incorporated with no difference between groups (mean, 3.8 ± 0.6 target vessels/patient; P = .92). Patients treated by t-Branch device had larger mean aneurysm diameter (79 ± 16 vs 66 ± 10 mm; P = .0006). All patients had transbrachial approach. Technical success was achieved in all patients in both groups. Patients treated by LP-PGS devices had lower radiation dose (1250 ± 849 vs 3154 ± 2421 mGy; P = .003) and shorter operating time for complete device deployment (105 ± 42 vs 123 ± 34 minutes; P = .043). There was no difference in mean operative time (252 ± 69 vs 273 ± 56 minutes; P = .23), fluoroscopy time (82 ± 29 vs 96 ± 35 minutes; P = .08) or contrast volume (163 ± 59 vs 197 ± 75 mL; P = .07) comparing LP-PGS and t-Branch respectively. There was no 30-day or in-hospital mortality. There were no differences in MAEs, which occurred in 18 patients (33%) in both groups (P > .05). CONCLUSIONS: Endovascular TAAA repair using the standard or LP-PGS multibranch stent graft was associated with high technical success, no mortality, and a low rate of MAEs in this study. Patients treated by upper extremity LP-PGS had shorter time to complete device deployment, suggesting decreased technical demand with preloaded systems.

Air Embolism During TEVAR: An Additional Flush Port on the Delivery System Pusher Significantly Reduces the Amount of Air Released During Deployment of a Thoracic Stent-Graft in an Experimental Setting.

PURPOSE: To investigate the influence of (1) an additional side port for flushing the hollow pusher in Zenith thoracic stent-graft delivery systems and (2) additional carbon dioxide flushing on the amount of air released during stent-graft deployment. METHODS: Twenty thoracic stent-grafts with an additional flush port to fill the hollow pusher were separated into 2 equal groups (C and D). Both groups were flushed with 20 mL of normal saline through the extra side port connected to the pusher and with 60 mL of saline through the regular flushing port. One group of grafts (group D) was additionally flushed with carbon dioxide through the regular flushing port prior to saline. All grafts were deployed into a curved plastic pipe attached to the bottom of a water-filled container. The released gas was recorded and measured using a calibrated setup. To evaluate the influence of the extra side port irrespective of the carbon dioxide flushing technique, group C was compared with a previously published reference group A without an extra side port that was flushed with the standard 60 mL of saline. RESULTS: Volumes of gas were released in various amounts from the stent-grafts during deployment. The average amount of released gas was 0.51 mL in group C and 0.07 mL in group D (p<0.001). The mean amount of gas from group C samples (0.51 mL) was also significantly lower (p=0.002) compared with the reference group (0.79 mL). CONCLUSION: Thoracic endografts release air during deployment. Reducing the air-filled space inside the pusher of the catheter assembly using an additional side port can significantly reduce the amount of released air. Using the extra side port in combination with the carbon dioxide flushing technique reduces gas release further to small volumes. In a clinical setting this could be a promising approach to lower the risk of air embolism and stroke during thoracic endovascular aortic repair.

Role of Re-entry Tears on the Dynamics of Type B Dissection Flap.

Mortality during follow-up after acute Type B aortic dissection is substantial with aortic expansion observed in over 59% of the patients. Lumen pressure differential is considered a prime contributing factor for aortic dilation after propagation. The objective of the study was to evaluate the relationship between changes in vessel geometry with and without lumen pressure differential post propagation in an ex vivo porcine model with comparison with patient clinical data. A pulse duplicator system was utilized to propagate the dissection within descending thoracic porcine aortic vessels for set proximal (%circumference of the entry tear: 40%, axial length: 2 cm) and re-entry (50% of distal vessel circumference) tear geometry. Measurements of lumen pressure differential were made along with quantification of vessel geometry (n = 16). The magnitude of mean lumen pressure difference measured after propagation was low (~ 5 mmHg) with higher pressures measured in false lumen and as anticipated the pressure difference approached zero after the creation of distal re-entry tear. False lumen Dissection Ratio (FDR) defined as arc length of dissected wall divided by arc length of dissection flap, had mean value of 1.59 ± 0.01 at pressure of 120/80 mmHg post propagation with increasing values with increase in pulse pressure that was not rescued with the creation of distal re-entry tear (p < 0.01). An average FDR of 1.87 ± 0.27 was measured in patients with acute Type B dissection. Higher FDR value (FDR = 1 implies zero dissection) in the presence of distal re-entry tear demonstrates an acute change in vessel morphology in response to the dissection independent of local pressure changes challenges the re-apposition of the aortic wall.

Role of Pulse Pressure and Geometry of Primary Entry Tear in Acute Type B Dissection Propagation.

The hemodynamic and geometric factors leading to propagation of acute Type B dissections are poorly understood. The objective is to elucidate whether geometric and hemodynamic parameters increase the predilection for aortic dissection propagation. A pulse duplicator set-up was used on porcine aorta with a single entry tear. Mean pressures of 100 and 180 mmHg were used, with pulse pressures ranging from 40 to 200 mmHg. The propagation for varying geometric conditions (%circumference of the entry tear: 15-65%, axial length: 0.5-3.2 cm) were tested for two flap thicknesses (1/3rd and 2/3rd of the thickness of vessel wall, respectively). To assess the effect of pulse and mean pressure on flap dynamics, the %true lumen (TL) cross-sectional area of the entry tear were compared. The % circumference for propagation of thin flap (47 ± 1%) was not significantly different (p = 0.14) from thick flap (44 ± 2%). On the contrary, the axial length of propagation for thin flap (2.57 ± 0.15 cm) was significantly different (p < 0.05) from the thick flap (1.56 ± 0.10 cm). TL compression was observed during systolic phase. For a fixed geometry of entry tear (%circumference = 39 ± 2%; axial length = 1.43 ± 0.13 cm), mean pressure did not have significant (p = 0.84) effect on flap movement. Increase in pulse pressure resulted in a significant change (p = 0.02) in %TL area (52 ± 4%). The energy acting on the false lumen immediately before propagation was calculated as 75 ± 9 J/m2 and was fairly uniform across different specimens. Pulse pressure had a significant effect on the flap movement in contrast to mean pressure. Hence, mitigation of pulse pressure and restriction of flap movement may be beneficial in patients with type B acute dissections.

Role of aortic stent graft oversizing and barb characteristics on folding.

OBJECTIVE: To evaluate folding in infrarenal stent grafts in relation to oversizing, barb angle, and barb length using computed tomography images of stent grafts deployed in explanted bovine aortas. METHODS: Computed tomography data from an in vitro investigation on the effect of oversizing of 4% to 45% (n = 19), barb length of 2 to 7 mm (n = 11), and barb angle of 10° to 90° (n = 7) on device fixation were examined for instances of folding. Folding was classified as circumferential or longitudinal and quantified on an ordinal scale based on codified criteria. Cumulative fold ranking from 0 (no fold) to 6 (two severe folds) for each deployment was used as the measure of folding observed. RESULTS: Of the 37 cases, cumulative mean ± standard deviation fold ranking for stent grafts oversized >30% (n = 5) was significantly greater than the rest (3.4 ± 1.7 vs 0.5 ± 1.2, respectively; Mann-Whitney U test; P < .005). When barb length was varied from 2 to 7 mm (oversizing held at 10%-20%), folding was noted in one of 11 cases. Similarly, when barb angle was varied from 0° (vertical) to 90° (horizontal), folding was not noted in any of the seven cases. The pullout force was not significantly different between stent grafts with and without folding (5.4 ± 1.95 vs 5.12 ± 1.89 N, respectively; P > .5). At least one instance of folding was noted in the seven of seven (100%) stent grafts with oversizing >23.5% and in only five of 30 (14%) stent grafts with oversizing <23.5%. CONCLUSIONS: Stent graft folding was prevalent when oversized >30%. Large variations in barb length and angle did not aggravate folding risk when oversized within the recommended range of 10% to 20%.

Biomechanical failure properties and microstructural content of ruptured and unruptured abdominal aortic aneurysms.

PURPOSE: To test the hypothesis that ruptured abdominal aortic aneurysms (AAA) are globally weaker than unruptured ones. METHODS: Four ruptured and seven unruptured AAA specimens were harvested whole from fresh cadavers during autopsies performed over an 18-month period. Multiple regionally distributed longitudinally oriented rectangular strips were cut from each AAA specimen for a total of 77 specimen strips. Strips were subjected to uniaxial extension until failure. Sections from approximately the strongest and weakest specimen strips were studied histologically and histochemically. From the load-extension data, failure tension, failure stress and failure strain were calculated. Rupture site characteristics such as location, arc length of rupture and orientation of rupture were also documented. RESULTS: The failure tension, a measure of the tissue mechanical caliber was remarkably similar between ruptured and unruptured AAA (group mean ± standard deviation of within-subject means: 11.2±2.3 versus 11.6±3.6N/cm; p=0.866 by mixed model ANOVA). In post-hoc analysis, there was little difference between the groups in other measures of tissue mechanical caliber as well such as failure stress (95±28 versus 98±23 N/cm(2); p=0.870), failure strain (0.39±0.09 versus 0.36±0.09; p=0.705), wall thickness (1.7±0.4 versus 1.5±0.4mm; p=0.470) , and % coverage of collagen within tissue cross section (49.6±12.9% versus 60.8±9.6%; p=0.133). In the four ruptured AAA, primary rupture sites were on the lateral quadrants (two on left; one on left-posterior; one on right). Remarkably, all rupture lines had a longitudinal orientation and ranged from 1 to 6 cm in length. CONCLUSION: The findings are not consistent with the hypothesis that ruptured aortic aneurysms are globally weaker than unruptured ones.

The effect of proteolytic treatment on plastic deformation of porcine aortic tissue.

The objective of this work was to assess whether selective proteolysis of elastin and/or collagen in a porcine aorta followed by mechanical creep loading would result in an aneurysm-like permanent tissue stretch. The underlying motivations were to (1) test the feasibility of developing an in vitro abdominal aortic aneurysm (AAA) model, and (2) understand what role, if any, that passive creep-induced stretching plays in aneurysmal dilation. Multiple circumferentially oriented flat specimen strips were cut from the porcine thoracic aorta of ten adult pigs. Specimens were subjected to one of six treatment protocols: Untreated controls (UC;N=23), complete elastin degradation (E;N=10), partial elastin degradation (E(p);N=10), partial collagen degradation (C(p);N=22), and partial degradation of both elastin and collagen (E(p)+C(p);N=3). All specimens were then subjected to cyclic creep (10 min/cycle) with increasing load amplitude until failure. The zero-load strain prior to the creep cycle where failure occurred was defined as load-induced plastic strain. The plastic strain induced by treatment alone, creep loading alone and the total was determined for all specimens. The total plastic strain was significantly greater for E (mean +/- SD = 48.2 +/-17.6,p<0.005), E(p)(41.6+/-11.1,p<0.0005), but not for E(p)+C(p)(48.9+/-21.6,p=0.17) and C(p)(22.2+/-12.8,p=0.14) compared to UC (17.7+/-6.1). Of the total plastic strain, treatment-induced plastic strain was high for those specimens subjected to partial or total elastin degradation (E,E(p),E(p)+C(p)), but not for those where elastin was intact (C(p)). However, load-induced plastic strain in the treated specimens was not different in any of the treated groups compared to controls. Maximum total plastic strain of 78.6% was induced in one porcine aortic tissue from the E group. Even this is far lower than what would be needed for creating a realistic in vitro AAA model. Our findings do not support the feasibility of developing an in vitro AAA by enzymolysis followed by passive stretching of the aorta. The findings also suggest that AAA formation is unlikely to be a passive creep-induced stretching of a proteolytically degraded aortic wall as conventional thinking may suggest, but rather may be predominantly due to growth and remodeling of the aortic wall.

Role of graft oversizing in the fixation strength of barbed endovascular grafts.

PURPOSE: The role of endovascular graft oversizing on risk of distal graft migration following endovascular aneurysm repair for abdominal aortic aneurysm is poorly understood. A controlled in vitro investigation of the role of oversizing in graft-aorta attachment strength for endovascular grafts (EVGs) with barbs was performed. METHODS: Barbed stent grafts (N = 20) with controlled graft oversizing varying from 4-45% were fabricated while maintaining other design variables unchanged. A flow loop with physiological flow characteristics and a biosynthetic aortic aneurysm phantom (synthetic aneurysm model with a bovine aortic neck) were developed. The stent grafts were deployed into the aortic neck of the bio-synthetic aortic aneurysm phantom under realistic flow conditions. Computed tomography imaging of the graft-aorta complex was used to document attachment characteristics such as graft apposition, number of barbs penetrated, and penetration depth and angle. The strength of graft attachment to the aortic neck was assessed using mechanical pullout testing. Stent grafts were categorized into four groups based on oversizing: 4-10%; 11-20%; 21-30%; and greater than 30% oversizing. RESULTS: Pullout force, a measure of post-deployment fixation strength was not different between 4-10% (6.23 +/- 1.90 N), 11-20% (6.25 +/- 1.84 N) and 20-30% (5.85 +/- 1.89 N) groups, but significantly lower for the group with greater than 30% oversizing (3.67 +/- 1.41 N). Increasing oversizing caused a proportional decrease in the number of barbs penetrating the aortic wall (correlation = -0.83). Of the 14 barbs available in the stent graft, 89% of the barbs (12.5 of 14 on average) penetrated the aortic wall in the 4-10% oversizing group while only 38% (5.25 of 14) did for the greater than 30% group (P < .001). Also, the stent grafts with greater than 30% oversizing showed significantly poorer apposition characteristics such as eccentric compression or folding of the graft perimeter. The number and depth of barb penetration were found to be positively correlated to pullout force. CONCLUSION: Greater than 30% graft oversizing affects both barb penetration and graft apposition adversely resulting in a low pullout force in this in vitro model. Barbed stent grafts with excessive oversizing are likely to result in poor fixation and increased risk of migration.

Regional distribution of wall thickness and failure properties of human abdominal aortic aneurysm.

The regional distribution of wall thickness and failure properties in human abdominal aortic aneurysm (AAA) was explored. Three unruptured and one ruptured AAA were harvested as a whole during necropsy. Thickness was measured at about every 1.5 cm(2) wall surface area for an average of 100 measurement sites per AAA. Multiple longitudinally oriented rectangular specimen strips were cut at various locations from each AAA for a total of 48 strips. The strips were subjected to uniaxial extension until failure. Wall thickness varied regionally and between AAA from as low as 0.23 mm at a rupture site to 4.26 mm at a calcified site (median=1.48 mm). Wall thickness was slightly lower in the posterior and right regions. The failure tension (ultimate) of specimen strips varied regionally and between AAA from 5.5 N/cm close to a blister site in the ruptured AAA to 42.3N/cm at the undilated neck of a 4 cm diameter unruptured AAA (median=14.8 N/cm). Failure stress (ultimate) varied from 33.6 to 235.1N/cm(2) (median=126.6N/cm(2)). There was no perceptible pattern in failure properties along the circumference. Failure tension of specimen strips at or close to blisters was mostly low. The rupture site in the ruptured aneurysm had the lowest recorded wall thickness of 0.23 mm with only slightly higher readings within a 1cm radius. The failure tension of the specimen strip close to the rupture site was low (11.1 N/cm) compared to its neighborhood in the ruptured aneurysm.

Introduction to biomechanics related to endovascular repair of abdominal aortic aneurysm.

Biomechanical issues of practical relevance to the physician in the clinical management of patients undergoing endovascular repair (EVR) of their abdominal aortic aneurysms (AAA) is discussed. Following a brief description of key terms in vascular biomechanics, background on the current state of knowledge in the biomechanics of AAA pathogenesis and rupture is provided. This is followed by a discussion of key issues of biomechanical relevance in EVR such as the mechanics of endotension, the notion of intraaneurysmal sac pressure and potential pitfalls of techniques used to measure them, mechanics of graft fracture/kinking, and graft migration. The discussions are intended to provide an overview of this field to physicians.