Stenting of a hepatic artery pseudoaneurysm rupture secondary to a celiac artery dissection

Hepatic artery (HA) pseudoaneurysm rupture is a rare and potentially lethal pathology. We present the case of a celiac artery dissection complicated by an HA pseudoaneurysm rupture that was treated successfully with endovascular stenting. The patient's postoperative course was uncomplicated, and he was further evaluated for an underlying connective tissue disorder. There is no standard treatment for a ruptured HA pseudoaneurysm, although transarterial embolization is most frequently reported. This report demonstrates that self-expanding stent grafts are effective in the emergent repair of HA pseudoaneurysm rupture.

Early Financial Outcomes of Physician Modified Endograft Programs are Dictated by Device Cost

INTRODUCTION

Physician-modified endografts (PMEGs) have been used for repair of thoracoabdominal aortic aneurysms (TAAAs) for 2 decades with good outcomes but limited financial data. This study compared the financial and clinical outcomes of PMEGs to the Cook Zenith-Fenestrated (ZFEN) graft and open surgical repair (OSR).

METHODS

A retrospective review of financial and clinical data was performed for all patients who underwent endovascular or OSR of juxtarenal aortic aneurysms and TAAAs from January 2018 to December 2022 at an academic medical center. Clinical presentation, demographics, operative details, and outcomes were reviewed. Financial data was obtained through the institution's finance department. The primary end point was contribution margin (CM).

RESULTS

Thirty patients met inclusion criteria, consisting of twelve PMEG, seven ZFEN, and eleven open repairs. PMEG repairs had a total CM of -$110,000 compared to $18,000 for ZFEN and $290,000 for OSR. Aortic and branch artery implants were major cost-drivers for endovascular procedures. Extent II TAAA repairs were the costliest PMEG procedure, with a total device cost of $59,000 per case. PMEG repairs had 30-d and 1-y mortality rates of 8.3% which was not significantly different from ZFEN (0.0%, P = 0.46; 0.0%, P = 0.46) or OSR (9.1%, P = 0.95; 18%, P = 0.51). Average intensive care unit and hospital stay after PMEG repairs were comparable to ZFEN and shorter than OSR.

CONCLUSIONS

Our study suggests that PMEG repairs yield a negative CM. To make these cases financially viable for hospital systems, device costs will need to be reduced or reimbursement rates increased by approximately $8800.

Locoregional Anesthesia's Association With Reduced Intensive Care Unit Stay After Elective Endovascular Aneurysm Repair: Impact of Temporal Changes in Practice Patterns

BACKGROUND

Elective endovascular aneurysm repair (EVAR) can be performed via local anesthetics and/or regional (epidural or spinal) anesthesia (locoregional [LR]), versus general anesthesia (GA), conferring reduced intensive care unit (ICU) and hospital stays. Current analyses fail to account for temporal changes in vascular practice. Therefore, this study aimed to confirm reductions in ICU and hospital stays among LR patients while accounting for changes in practice patterns.

MATERIALS AND METHODS

Using the Society for Vascular Surgery's Vascular Quality Initiative, elective EVARs from August 2003 to June 2021 were grouped into LR or GA. Outcomes included ICU admission and prolonged hospital stay (>2 d). Procedures were stratified into groups of 2 y periods, and outcomes were analyzed within each time period. Univariable and multivariate analyses were used to assess outcomes.

RESULTS

LR was associated with reduced ICU admissions (22.3% versus 32.1%, P < 0.001) and prolonged hospital stays (14.3% versus 7.9%, P < 0.001) overall. When stratified by year, LR maintained its association with reduced ICU admissions in 2014-2015 (21.8% versus 34.0%, P < 0.001), 2016-2017 (23.6% versus 31.6%, P < 0.001), 2018-2019 (18.5% versus 30.2%, P < 0.001), and 2020-2021 (15.8% versus 28.8%, P < 0.001), although this was highly facility dependent. LR was associated with fewer prolonged hospital stays in 2014-2015 (15.6% versus 20.4%, P = 0.001) and 2016-2017 (13.3% versus 16.6%, P = 0.006) but not after 2017.

CONCLUSIONS

GA and LR have similar rates of prolonged hospital stays after 2017, while LR anesthesia was associated with reduced rates of ICU admissions, although this is facility-dependent, providing a potential avenue for resource preservation in patients suitable for LR.

Survival, Reintervention, and Value of Open and Endovascular Repair for Chronic Mesenteric Ischemia

BACKGROUND

There are limited analyses of survival and postoperative outcomes in chronic mesenteric ischemia (CMI) using data from large cohorts. Current guidelines recommend open repair (OR) for younger, healthier patients when long-term benefits outweigh increased perioperative risks or for poor endovascular repair (ER) candidates. This study investigates whether long-term survival, reintervention, and value differ between these treatment modalities.

METHODS

A retrospective cohort analysis was performed on data extracted from the Statewide Planning and Research Cooperative System, the New York statewide all-payer database containing demographics, diagnoses, treatments, and charges. Patients were selected for CMI and subsequent ER or OR using International Classification of Diseases, Ninth Revision codes. Patients with peripheral arterial disease were excluded to account for ambiguity in the International Classification of Diseases, Ninth Revision procedure code for angioplasty of noncoronary vessels, which includes angioplasty of upper and lower extremity vessels. Kaplan-Meier analysis was used to compare 1-year and 5-year survival and reintervention between treatment modalities using a propensity-matched cohort. Cox proportional hazards testing was performed to find factors associated with 1-year and 5-year survival and reintervention. Analysis of procedural value was performed using linear regression.

RESULTS

From 2000 to 2014, 744 patients met inclusion criteria. Of these, 209 (28.1%) underwent OR and 535 (71.9%) ER. No difference between propensity-matched groups was found in 1-year (P = 0.46) or 5-year (P = 0.91) survival. Congestive heart failure (hazard ratio [HR]: 2.8, 95% confidence interval [CI]: 1.7-4.4; P < 0.01), cancer (HR: 2.8, 95% CI: 1.3-5.8; P < 0.01), and dysrhythmia (HR: 1.8, 95% CI: 1.1-2.8; P = 0.02) correlated with 1-year mortality. Cancer (HR: 2.9, 95% CI: 1.6-5.5; P < 0.01), congestive heart failure (HR: 2.2, 95% CI: 1.5-3.2; P < 0.01), chronic pulmonary disease (HR: 1.4, 95% CI: 1.0-2.0; P = 0.04), and age (HR: 1.03, 95% CI: 1.01-1.05; P < 0.01) correlated with 5-year mortality. Treatment modality was not associated with reintervention at 1 year on Kaplan-Meier analysis (P = 0.29). However, ER showed increased instances of reintervention at 5 years (P < 0.01). Additionally, ER was associated with an increased 5-year value (0.7 ± 0.9 vs. 0.5 ± 0.5 life years/charges at index admission [$10k], P < 0.01; b coefficient: 0.2, 95% CI: 0.1-0.4, P < 0.01).

CONCLUSIONS

This is the largest retrospective propensity-matched single-study cohort to analyze long-term survival outcomes after intervention for CMI. Long-term mortality was independent of treatment modality and rather was associated with patient comorbidities. Therefore, treatment selection should depend on anatomic considerations and long-term value. ER should be considered over OR in patients with amenable anatomy based on the superior procedural value.

Intermediate pressure-normalized principal wall strain values are associated with increased abdominal aortic aneurysmal growth rates

Introduction

Current abdominal aortic aneurysm (AAA) assessment relies on analysis of AAA diameter and growth rate. However, evidence demonstrates that AAA pathology varies among patients and morphometric analysis alone is insufficient to precisely predict individual rupture risk. Biomechanical parameters, such as pressure-normalized AAA principal wall strain (ε ρ + ¯ /PP, %/mmHg), can provide useful information for AAA assessment. Therefore, this study utilized a previously validated ultrasound elastography (USE) technique to correlate ε ρ + ¯ /PP with the current AAA assessment methods of maximal diameter and growth rate.

Methods

Our USE algorithm utilizes a finite element mesh, overlaid a 2D cross-sectional view of the user-defined AAA wall, at the location of maximum diameter, to track two-dimensional, frame-to-frame displacements over a full cardiac cycle, using a custom image registration algorithm to produce ε ρ + ¯ /PP. This metric was compared between patients with healthy aortas and AAAs (≥3 cm) and compared between small and large AAAs (≥5 cm). AAAs were then separated into terciles based on ε ρ + ¯ /PP values to further assess differences in our metric across maximal diameter and prospective growth rate. Non-parametric tests of hypotheses were used to assess statistical significance as appropriate.

Results

USE analysis was conducted on 129 patients, 16 healthy aortas and 113 AAAs, of which 86 were classified as small AAAs and 27 as large. Non-aneurysmal aortas showed higher ε ρ + ¯ /PP compared to AAAs (0.044 ± 0.015 vs. 0.034 ± 0.017%/mmHg, p = 0.01) indicating AAA walls to be stiffer. Small and large AAAs showed no difference in ε ρ + ¯ /PP. When divided into terciles based on ε ρ + ¯ /PP cutoffs of 0.0251 and 0.038%/mmHg, there was no difference in AAA diameter. There was a statistically significant difference in prospective growth rate between the intermediate tercile and the outer two terciles (1.46 ± 2.48 vs. 3.59 ± 3.83 vs. 1.78 ± 1.64 mm/yr, p = 0.014).

Discussion

There was no correlation between AAA diameter and ε ρ + ¯ /PP, indicating biomechanical markers of AAA pathology are likely independent of diameter. AAAs in the intermediate tercile of ε ρ + ¯ /PP values were found to have nearly double the growth rates than the highest or lowest tercile, indicating an intermediate range of ε ρ + ¯ /PP values for which patients are at risk for increased AAA expansion, likely necessitating more frequent imaging follow-up.

Impact of calcified plaque volume on technical and 3-year outcomes after transcarotid artery revascularization

OBJECTIVE

We sought to quantify the percent calcification within carotid artery plaques and assess its impact on percent residual stenosis and rate of restenosis in patients undergoing transcarotid artery revascularization for symptomatic and asymptomatic carotid artery stenosis.

METHODS

A retrospective review of prospectively collected institutional Vascular Quality Initiative data was performed to identify all patients undergoing transcarotid artery revascularization from December 2015 to June 2021 (n = 210). Patient and lesion characteristics were extracted. Using a semiautomated workflow, preoperative computed tomography head and neck angiograms were analyzed to determine the calcified plaque volume in distal common carotid artery and internal carotid artery plaques. Intraoperative digital subtraction angiograms were reviewed to calculate the percent residual stenosis post-intervention according to North American Symptomatic Carotid Endarterectomy Trial criteria. Peak systolic velocity and end-diastolic velocity were extracted from outpatient carotid duplex ultrasound examinations. Univariate logistic regression was performed to analyze the relationship of calcium volume percent and Vascular Quality Initiative lesion calcification to percent residual stenosis in completion angiograms. Kaplan-Meier analysis examined the relationship between calcium volume percent and in-stent stenosis over 36 months.

RESULTS

One hundred ninety-seven carotid arteries were preliminarily examined. Predilation was performed in 87.4% of cases with a mean balloon diameter of 5.1 ± 0.7 mm and a mean stent diameter was 8.8 ± 1.1 mm. The mean calcium volume percent was 11.9 ± 12.4% and the mean percent residual stenosis was 16.1 ± 15.6%. Univariate logistic regression demonstrated a statistically significant difference between calcium volume percent and percent residual stenosis (odds ratio [OR], 1.324; 95% confidence interval [CI], 1.005-1.746; P = .046). Stratified by quartile, only the top 25% of calcified plaques (>18.7% calcification) demonstrated a statistically significant association with higher percent residual stenosis (OR, 2.532; 95% CI, 1.049-6.115; P =.039). There was no statistical significance with lesion calcification (OR, 1.298; 95% C,: 0.980-1.718; P = .069). A Kaplan-Meier analysis demonstrated a statistically significant increase in the rate of in-stent stenosis during a 36-month follow-up for lesions containing >8.2% calcium volume (P = .0069).

CONCLUSIONS

A calcium volume percent of >18.7% was associated with a higher percent residual stenosis, and a calcium volume percent of >8.2% was associated with higher in-stent stenosis at 36 months. There was one clinically diagnosed stroke during the follow-up period, demonstrating the overall safety of the procedure.

Gore TAG thoracic branch endograft for treatment of a subacute type B aortic dissection complicated by rupture

An 80-year-old man presented with a subacute zone 3-5 type B aortic dissection complicated by rupture and visceral and lower extremity malperfusion. He underwent emergent zone 2 repair with a Gore TAG thoracic branch endograft with inclusion of the left subclavian artery for a dominant left vertebral artery. The patient's postoperative course was uncomplicated. Type B aortic dissections can be anatomically complex, and rupture is a rare complication in the subacute phase. We report the novel use of a Gore TAG thoracic branch endograft for the management of type B aortic dissection complicated by rupture and demonstrate its feasibility for patients with type B aortic dissection complicated by rupture.

Locoregional anesthesia is associated with reduced hospital stay and need for intensive care unit care of elective endovascular aneurysm repair patients in the Vascular Quality Initiative

OBJECTIVE

It has been shown local or regional anesthetic techniques are a feasible alternative to general anesthesia for endovascular aortic aneurysm repair (EVAR). However, studies to date have shown controversial findings with respect to the benefit of locoregional anesthesia (LR) in the elective setting. The objective of this study is to compare postoperative outcomes between LR and general anesthesia (GA) in the setting of elective EVAR, using a large, multicenter database.

METHODS

Using the Society for Vascular Surgery Vascular Quality Initiative database, we retrospectively analyzed all patients who underwent elective EVAR from August 2003 to June 2021. Patients were grouped by anesthetic type based on the level of consciousness afforded by the anesthetic: local or regional anesthesia (LR) vs GA. Primary outcomes were total postoperative hospital length-of-stay (LOS) and intensive care unit (ICU) LOS. Propensity score matching was used for risk adjustment and to analyze the primary outcomes with confirmatory analysis using logistic or linear regression, as appropriate, in single and multilevel models. Secondary outcomes were 30-day mortality, 1-year mortality, postoperative outcomes, operative time, fluoroscopy time, and reoperation rate. These were analyzed following propensity score matching as well as using logistic regression and Cox proportional hazard regression in single and multilevel models, as appropriate.

RESULTS

A total of 50,809 patients underwent elective EVAR from 2003 to 2021. Of these, 4302 repairs used LR (8.5%) and 46,507 (91.5%) were performed under GA. After employing propensity score matching, two groups of 3027 patients were produced. These showed no significant difference in 30-day mortality (odds ratio, 1.22; P = .53), 1-year mortality (hazard ratio, 1.06; P = .62), or any postoperative outcomes. LR was found to be significantly associated with shorter hospital stays (≤2 days) (12.5% vs 14.8%; P = .01), decreased ICU utilization (19.3% vs 30.6%; P < .001), decreased operative time (110.8 vs 117.3 minutes; P < .001), decreased fluoroscopy time (21.0 vs 22.7 minutes; P < .001), and a slight reduction in reoperation rate (1.2% vs 1.9%; P = .02), which all remained significant following single-level and multilevel multivariate analyses accounting for hospital and physician random effects.

CONCLUSIONS

These data suggest that LR anesthesia is safe and may offer advantages in reducing resource utilization for patients undergoing elective EVAR, primarily based on associations with reduced ICU care and reduced hospital stay. Given these findings, LR may prove an advantageous technique in appropriately selected patient populations.

Totally percutaneous endovascular repair of HeartMate 3 ventricular assistive device outflow graft pseudoaneurysm

The rate of heart failure and subsequent placement of left ventricular assistive devices (LVADs) has been increasing. The extra-anatomic placement of the LVAD and outflow graft presents a challenging problem for repair when complications arise. The present report describes a case of a 63-year-old man who had presented with acute pseudoaneurysm of the outflow graft of his recently placed LVAD. Percutaneous access of the left subclavian artery and percutaneous, transthoracic access of the outflow graft was obtained to allow for sheath placement and stent deployment within the outflow graft. The patient underwent successful endovascular repair of the defect without complications.

(PEAK) WALL STRESS AS AN INDICATOR OF ABDOMINAL AORTIC ANEURYSM SEVERITY

Abdominal aortic aneurysms, which consist of dilatations of the infra-renal aorta by at least 1.5 times of its normal diameter, are becoming a leading cause of death worldwide. Rupture often occurs unexpectedly, before a repair procedure is conducted. The AAA maximum diameter has been used as a clinical criterion to monitor AAA severity. However, assessment of AAA rupture risk requires knowledge of wall stress and wall strength at the potential rupture location. We conducted a study on 37 patient specific CT datasets to investigate the benefits of using peak wall stress instead of D_max for AAA rupture severity. Correlation between PWS and 24 geometric indices and biomechanical factors was studied where eleven of them showed a statistically significant correlation with PWS. A Finite Element Analysis Rupture Index was used to conclude that the use of D _max as a single predictor of AAA behavior and severity may be insufficient based on our patient population with a D_max smaller than the 5.5 cm, clinically recommended repair threshold.

Manufacturing Abdominal Aorta Hydrogel Tissue-Mimicking Phantoms for Ultrasound Elastography Validation

Ultrasound (US) elastography, or elasticity imaging, is an adjunct imaging technique that utilizes sequential US images of soft tissues to measure the tissue motion and infer or quantify the underlying biomechanical characteristics. For abdominal aortic aneurysms (AAA), biomechanical properties such as changes in the tissue's elastic modulus and estimates of the tissue stress may be essential for assessing the need for the surgical intervention. Abdominal aortic aneurysms US elastography could be a useful tool to monitor AAA progression and identify changes in biomechanical properties characteristic of high-risk patients. A preliminary goal in the development of an AAA US elastography technique is the validation of the method using a physically relevant model with known material properties. Here we present a process for the production of AAA tissue-mimicking phantoms with physically relevant geometries and spatially modulated material properties. These tissue phantoms aim to mimic the US properties, material modulus, and geometry of the abdominal aortic aneurysms. Tissue phantoms are made using a polyvinyl alcohol cryogel (PVA-c) and molded using 3D printed parts created using computer aided design (CAD) software. The modulus of the phantoms is controlled by altering the concentration of PVA-c and by changing the number of freeze-thaw cycles used to polymerize the cryogel. The AAA phantoms are connected to a hemodynamic pump, designed to deform the phantoms with the physiologic cyclic pressure and flows. Ultra sound image sequences of the deforming phantoms allowed for the spatial calculation of the pressure normalized strain and the identification of mechanical properties of the vessel wall. Representative results of the pressure normalized strain are presented.

Hypoxia and Ischemia Promote a Maladaptive Platelet Phenotype

Supplemental Digital Content is available in the text.

Objective—

Reduced blood flow and tissue oxygen tension conditions result from thrombotic and vascular diseases such as myocardial infarction, stroke, and peripheral vascular disease. It is largely assumed that while platelet activation is increased by an acute vascular event, chronic vascular inflammation, and ischemia, the platelet activation pathways and responses are not themselves changed by the disease process. We, therefore, sought to determine whether the platelet phenotype is altered by hypoxic and ischemic conditions.

Approach and Results—

In a cohort of patients with metabolic and peripheral artery disease, platelet activity was enhanced, and inhibition with oral antiplatelet agents was impaired compared with platelets from control subjects, suggesting a difference in platelet phenotype caused by the disease. Isolated murine and human platelets exposed to reduced oxygen (hypoxia chamber, 5% O₂) had increased expression of some proteins that augment platelet activation compared with platelets in normoxic conditions (21% O₂). Using a murine model of critical limb ischemia, platelet activity was increased even 2 weeks postsurgery compared with sham surgery mice. This effect was partly inhibited in platelet-specific ERK5 (extracellular regulated protein kinase 5) knockout mice.

Conclusions—

These findings suggest that ischemic disease changes the platelet phenotype and alters platelet agonist responses because of changes in the expression of signal transduction pathway proteins. Platelet phenotype and function should, therefore, be better characterized in ischemic and hypoxic diseases to understand the benefits and limitations of antiplatelet therapy.

Abstract 140: Real-time Modulation of Platelet Phenotype and Vein Wall Biology in Patients with Chronic Venous Insufficiency

Background: The role of antiplatelet agents in the modulation of arterial disease is well described, but a paucity of data exists regarding their role in chronic venous insufficiency (CVI). We hypothesize that platelet responses to various antiplatelet agents are altered when comparing platelet function within refluxing and non-refluxing vein segments. Additionally, changes in platelet phenotype may alter vein wall biology.

Methods: Isolated platelets were obtained simultaneously from the patient antecubital vein (ACV) and a refluxing greater saphenous vein (GSV) during surgical phlebectomy and compared to platelets from healthy individuals. Non-refluxing GSV was harvested for coronary bypass. Platelet surface receptor activation was assessed through P2Y12 (clopidogrel), PAR1 (vorapaxar), and thromboxane (aspirin) pathways by flow cytometry for p-selectin. Immunoblotting assessed CD41 (platelet) and CD45 (WBC) within the wall of vein samples.

Results: Platelets from refluxing GSV showed a significant increase in reactivity via all platelet signaling pathways, especially P2Y12 and thromboxane when compared to platelets from the ACV in the same patient. Conversely, platelets collected from the ACV in CVI patients showed a significant decrease in reactivity to all agonists compared to ACV in healthy individuals without CVI. Most notably, GSV from a patient with CVI had a reduction in CD41 content, but a seven-fold increase in the CD45:CD41 ratio, compared to GSV from healthy people (Figure).

Conclusions: Platelet activation by these clinically relevant pathways is enhanced locally in the refluxing GSV, yet systemic, circulating platelets isolated from CVI patients are 2-3-fold less active than systemic platelets from healthy people. Our data suggest that reflux may locally alter the circulating platelet phenotype and in turn also have a role in remodeling the vein wall.

Toward modeling the effects of regional material properties on the wall stress distribution of abdominal aortic aneurysms

The overall geometry and different biomechanical parameters of an abdominal aortic aneurysm (AAA), contribute to its severity and risk of rupture, therefore they could be used to track its progression. Previous and ongoing research efforts have resorted to using uniform material properties to model the behavior of AAA. However, it has been recently illustrated that different regions of the AAA wall exhibit different behavior due to the effect of the biological activities in the metalloproteinase matrix that makes up the wall at the aneurysm site. In this work, we introduce a non-invasive patient-specific regional material property model to help us better understand and investigate the AAA wall stress distribution, peak wall stress (PWS) severity, and potential rupture risk. Our results indicate that the PWS and the overall wall stress distribution predicted using the proposed regional material property model, are higher than those predicted using the traditional homogeneous, hyper-elastic model (p <1.43E-07). Our results also show that to investigate AAA, the overall geometry, presence of intra-luminal thrombus (ILT), and loading condition in a patient specific manner may be critical for capturing the biomechanical complexity of AAAs.

Detecting Regional Stiffness Changes in Aortic Aneurysmal Geometries Using Pressure-Normalized Strain

Transabdominal ultrasound elasticity imaging could improve the assessment of rupture risk for abdominal aortic aneurysms by providing information on the mechanical properties and stress or strain states of vessel walls. We implemented a non-rigid image registration method to visualize the pressure-normalized strain within vascular tissues and adapted it to measure total strain over an entire cardiac cycle. We validated the algorithm's performance with both simulated ultrasound images with known principal strains and anatomically accurate heterogeneous polyvinyl alcohol cryogel vessel phantoms. Patient images of abdominal aortic aneurysm were also used to illustrate the clinical feasibility of our imaging algorithm and the potential value of pressure-normalized strain as a clinical metric. Our results indicated that pressure-normalized strain could be used to identify spatial variations in vessel tissue stiffness. The results of this investigation were sufficiently encouraging to warrant a clinical study measuring abdominal aortic pressure-normalized strain in a patient population with aneurysmal disease.

Abstract 150: Hypoxia and Ischemia Promote a Maladaptive Platelet Phenotype

Background: An understudied area of platelet biology is that ischemic diseases such as peripheral vascular disease (PVD) can alter the platelet phenotype, and this may lead to unpredictable effects of anti-platelet agents.

Methods: Isolated murine and human platelets were exposed to a reduced oxygen environment (hypoxia chamber, 5% O 2 ). Platelet activation was assessed as mean fluorescence intensity (MFI) of surface p-selectin by flow cytometry, and morphologic changes by confocal microscopy. A murine model of critical limb ischemia (CLI) was used to assess changes in platelet activity in wild-type (WT) and in platelet ERK5 -/- mice. Limb blood flow was assessed by laser Doppler imaging. Hypoxia was additionally examined in mice by unilateral pneumonectomy. Western blotting was used to assess protein expression.

Results: In human platelets ex vivo at 5% O 2 , platelet activation increased to 5076 MFI±409 from 3548 MFI±187 at 20% O 2 (P=0.005). With the ERK5 inhibitor XMD892, platelet activation at 5% O 2 decreased from 5677 MFI±312 to 3175 MFI±247 (p=0.001). In a murine model of PVD, enhanced platelet activation was sustained for weeks vs. sham, and limb blood flow in platelet ERK5 -/- mice one week after ischemia was augmented by 26%: 0.61±0.03 vs 0.87±0.03 vs, WT mice (p=0.0002), with 50% less platelet activity. In mice with unilateral pneumonectomy vs. sham surgery, observed hypoxia was accompanied by increased platelet ERK5 activation coincident with enhanced platelet activation. In patients with CLI, augmented platelet activation in spite of aspirin treatment was observed via the thromboxane and the PAR1 receptors, and especially via P2Y 12 receptor.

Conclusions: Hypoxia and ischemic tissue injury, such as with critical limb ischemia, change the phenotype of the platelet, promoting a pro-thrombotic state that is partly dependent on platelet ERK5. Platelet phenotype and function should be better characterized in ischemic diseases.

Abstract 105: Association of Viscoelastic Material Properties and Extracellular Matrix Remodeling in Human Abdominal Aortic Aneurysmal Tissue

Objectives: Predicting rupture of abdominal aortic aneurysm (AAA) requires knowledge of both the rate of extracellular matrix (ECM) degradation and the pulsatile stress on the aortic tissue. The activity of matrix metallopeptidase 9 (MMP9) and its inhibitor, TIMP1, are associated with alterations in aortic ECM but it is unknown if these changes effect the dynamic viscoelastic properties. We hypothesize that increased levels of MMP9 within AAA tissue will be associated with a greater dynamic modulus (E*), as a surrogate of increased aortic wall stress.

Methods: Human aneurysmal aortic tissue was obtained at the time of open AAA repair (n=11) and age-matched non-aneurysmal cadavers (n=10). Uniaxial viscoelastic material properties were measured in the circumferential orientation under physiologic preload (110 mmHg) and cyclic strain (± 5%@1Hz). Quantitative histologic and immunohistochemistry were preformed using Fiji imaging software. Aortic MMP9 and TIMP1 content and activity were quantified using western blot and zymography.

Results: E* was greater (1862±464 vs 1362±405 kPa, p=0.02) in the AAA tissue as compared to non-aneurysmal tissue. AAA tissue contained less elastin (6.7±6.7 vs 23.4±8.7%, p=0.01) and a greater collagen/elastin ratio (19.9±20.6 vs 2.3±2.5%, p=0.05). Immunohistochemistry revealed 200% greater MMP9 content in the AAA tissue (Figure A & B, 0.61 vs 0.03%, p=0.03). Increased MMP9 content was confirmed using a western blot (0.43 vs 0.06 AU, p<0.01). No difference in relative MMP9 activity (4307 vs 2324 AU, p=0.25) or level of TIMP1 (0.03 vs 0.02, p=0.6) were observed. There was a positive linear correlation (Figure C, r 2 =0.47) between E* and MMP9 as determined by quantitative immunohistochemistry.

Conclusions: Our data suggests a positive relationship between E* and MMP9 content. Increased tissue stiffness may trigger MMP9 production resulting in a positive-feedback loop, progressively increasing aortic wall stress and rupture risk.

Outcomes for critical limb ischemia are driven by lower extremity revascularization volume, not distance to hospital

OBJECTIVE

The objective of this study was to identify relationships among geographic access to care, vascular procedure volume, limb preservation, and survival in patients diagnosed with critical limb ischemia (CLI).

METHODS

Using New York State administrative data from 2000 to 2013, we identified a patient's first presentation with CLI defined by International Classification of Diseases, Ninth Revision diagnosis and procedure codes. Distance from the patient's home to the index hospital was calculated using the centroids of the respective ZIP codes. A multivariable logistic regression model was employed to estimate the impact of distance, major lower extremity amputation (LEA) volume, and lower extremity revascularization (LER) volume on major amputation and 30-day mortality. Volumes and distances were analyzed in quintiles. The farthest distance quintile and the highest procedure volume quintiles were used as references for generating odds ratios (ORs).

RESULTS

There were 49,576 patients identified with an initial presentation of CLI. The median age was 73 years, 35,829 (73.2%) had Medicare as a primary insurer, 11,395 (23.0%) had a major amputation, and 4249 (8.6%) died within 30 days of admission. Patients in the closest distance quintile were more likely to undergo amputation (OR, 1.53 [1.39-1.68]; P < .0001). Patients who visited hospitals in the lowest LER volume quintile with at least one procedure per year faced higher 30-day mortality rates (OR, 2.05 [1.67-2.50]; P < .0001) and greater odds of amputation (OR, 9.94 [8.5-11.63]; P < .0001). Patients who visited hospitals in the lowest LEA volume quintile had lower odds of 30-day mortality (OR, 0.66 [0.50-0.87]; P = .0033) and lower odds of amputation (OR, 0.180 [0.142-0.227]; P < .0001).

CONCLUSIONS

Rates of major amputation are inversely associated with distance from the index hospital, whereas rates of both major amputation and mortality are inversely associated with LER volume. Rates of major amputation and mortality are directly associated with LEA volume. We believe that unless it is otherwise contraindicated, these data support consideration for selective referral of CLI patients to high-volume centers for LER regardless of distance. Within the context of value-based health care delivery, policy supporting regionalization of CLI care into centers of excellence may improve outcomes for these patients.

Abstract 105: Increased Dynamic Mechanical Energy Dissipation in Human Abdominal Aortic Aneurysm

Objectives: Individualized patient rupture risk for abdominal aortic aneurysms (AAA) remains elusive due to a limited understanding of the biomechanical events that trigger aneurysm growth and aortic wall failure. To date there has been a paucity of data describing how physiologic pulsatile energy is stored (E') and lost (E'') from AAA tissue. Our hypothesis is that AAA tissue dissipates more cyclic energy at a physiologic frequency, as determined by (E''/ E'), when compared to healthy aortic tissue.

Methods: Human healthy aortic and AAA samples were obtained from cadaveric and surgical specimens. Specimens were stored at 4 o C in 0.9%NS and mechanically tested within 36 hrs of explant. Uniaxial mechanical testing (ADMET BioTense) was performed in the circumferential orientation with the tissue pre-loaded to an equivalent physiologic stress of a 5 cm at a 110 mmHg mean pressure. A sinusoidal ±5% strain was applied at 1 Hz for 40 cycles with simultaneous force measurements. After mechanical testing, immunohistochemical staining was performed to confirm tissue viability.

Results: AAA tissue was significantly stiffer when compared to healthy aorta, as demonstrated by a greater average static modulus (E) 1555.4 ± 384 vs. 970 ± 128 kPa (n=5, p=0.03). Dynamic testing of the AAA tissue noted a significantly greater energy loss (E'') 137.8±36.7 vs. 43.1±21.7 (p<0.01) and loss ratio (E''/ E') 0.090 ± 0.023 vs. 0.044 ± 0.023 (p=0.02), when compared to normal specimens. Figure #1 compares the static modulus (E) to the loss ratio (E''/ E') for the aortic tissue specimens. Histologic analysis confirmed tissue viability during of all specimens.

Conclusions: Our data demonstrates that AAA tissue dissipates more energy (E'') and has a greater energy loss ratio (E''/ E'), suggesting that more pulsatile energy is dissipated in diseased tissue. Future work is needed to determine how this energy dissipation influences the biologic pathogenesis of AAA growth and rupture.

Abstract 256: 2D Ultrasound Measurements Can Quantify Relative Single-Plane Circumferential Strain in an Abdominal Aortic Aneurysm Model

OBJECTIVES: Current size-based assessments of AAA rupture potential do not accurately identify all patients at risk. True AAA rupture potential is related to hemodynamic and geometric factors involving wall strain and compliance. Our hypothesis is that transcutaneous ultrasound-derived strain measurements can identify heterogeneous aortic wall compliance toward predicting future rupture.

METHODS: A latex phantom with changes in wall thickness (0.05-0.25 inches) to simulate AAA morphology was tested on an in vitro hemodynamic simulator. A GE Vivid i ultrasound machine interrogated the phantom under uniform physiologic, pulsatile conditions. The circumferential strain and radial strain of uniform wall phantom versus asymmetric wall phantom was quantified.

RESULTS: Maximum circumferential strain (MCS) of the uniform wall thickness phantom was evenly distributed at 3.5% with an AP wall strain difference of 2.3% (Figure 1A). Maximum radial strain (MRS) was evenly distributed at 9% with an AP wall strain difference of 0%. MCS and MRS of the asymmetric wall thickness phantom were significantly increased to 30% and 36% respectively at the thinned anterior wall. AP wall strain difference was 22% (Figure 1B) and 10% respectively.

CONCLUSIONS: Using transcutaneous 2D ultrasound, we were able to quantify changes in strain due to wall compliance in an AAA phantom. Further development of this technology may provide for a non-invasive method of characterizing the hemodynamic and geometric properties of an AAA to predict rupture potential.

Abstract 424: Novel Computational Algorithm to Quantify Blood Flow and Vascular Resistance from Contrast Angiography with High Accuracy

OBJECTIVES: Contrast angiography can diagnose arterial occlusive disease but cannot provide hemodynamic data. Past work has attempted to calculate angiographic blood flow but clinical use has been limited by measurement error of >10%. Our hypothesis was that blood flow could be calculated from a contrast angiogram with <10% error through the application of a novel computational algorithm.

METHODS: A pulsatile, in vitro hemodynamic simulator with a light-based angiographic imaging system (InfiMed, Inc.) was used as the testing platform. Flow rates were varied through increases in outflow resistance and were directly measured with a Transonic flow meter (+/-4% error). An algorithm was designed to determine instantaneous flow from DICOM images using a combination of automatic vessel detection, segmentation, and time of flight bolus tracking. These calculated flow rates were compared to those directly measured.

RESULTS: The calculated flow rates (cc/min) were highly accurate when compared to those directly measured (4.1+/-3% error). Furthermore, time-density curves were accurate enough to detect relative changes in flow of 1.7 cc/sec reflecting changes in distal vascular resistance (Figure 1).

CONCLUSION: We conclude that using this approach, blood flow can be angiographically measured with increased accuracy relative to prior work. This may provide clinically reliable hemodynamic data to guide diagnostic and therapeutic interventions.