A simplified murine intimal hyperplasia model founded on a focal carotid stenosis

Murine models offer a powerful tool for unraveling the mechanisms of intimal hyperplasia and vascular remodeling, although their technical complexity increases experimental variability and limits widespread application. We describe a simple and clinically relevant mouse model of arterial intimal hyperplasia and remodeling. Focal left carotid artery (LCA) stenosis was created by placing 9-0 nylon suture around the artery using an external 35-gauge mandrel needle (middle or distal location), which was then removed. The effect of adjunctive diet-induced obesity was defined. Flowmetry, wall strain analyses, biomicroscopy, and histology were completed. LCA blood flow sharply decreased by ∼85%, followed by a responsive right carotid artery increase of ∼71%. Circumferential strain decreased by ∼2.1% proximal to the stenosis in both dietary groups. At 28 days, morphologic adaptations included proximal LCA intimal hyperplasia, which was exacerbated by diet-induced obesity. The proximal and distal LCA underwent outward and negative inward remodeling, respectively, in the mid-focal stenosis (remodeling indexes, 1.10 and 0.53). A simple, defined common carotid focal stenosis yields reproducible murine intimal hyperplasia and substantial differentials in arterial wall adaptations. This model offers a tool for investigating mechanisms of hemodynamically driven intimal hyperplasia and arterial wall remodeling.

Perivascular innate immune events modulate early murine vein graft adaptations

OBJECTIVE

Innate immunity drives numerous cardiovascular pathologies. Vein bypass grafting procedures are frequently accompanied by low-grade wound contamination. We hypothesized that a peri-graft innate immune challenge, via an outside-in route, augments inflammatory responses, which subsequently drive a component of negative vein graft wall adaptations; moreover, adipose tissue mediates this immune response.

METHODS

The inferior vena cava from a donor mouse was implanted into the common carotid artery of a recipient mouse utilizing a validated cuff technique (9-week-old male C57BL/6J mice). Slow-release low-dose (5 μg) lipopolysaccharide (LPS) (n = 9) or vehicle (n = 9) was applied peri-graft; morphologic analysis was completed (day 28). In parallel, vein-grafted mice received peri-graft LPS (n = 12), distant subcutaneous LPS (n = 6), or vehicle (n = 12), then day-1 and -3 harvest of grafts and adipose tissue for cytokines and toll-like receptor (TLR) signaling mRNA expression (qRT-PCR).

RESULTS

All recipient mice survived, and all vein grafts were patent. Acute low-dose local LPS challenge enhanced vein graft lumen loss (P = .04) and tended to augment intimal hyperplasia (P = .06). The surgical trauma of vein grafting universally upregulated key pro- and anti-inflammatory mediators within the day-1 graft wall, but varied on TLR signaling gene expression. Local and distant LPS accentuated these patterns until at least postoperative day 3. LPS challenge enhanced the inflammatory response in adipose tissue (locally > distantly); local LPS upregulated adipose TLR-4 dramatically.

CONCLUSIONS

Perivascular and distant inflammatory challenges potentiate the magnitude and duration of inflammatory responses in the early vein graft wall, negatively modulating wall adaptations, and thus, potentially contribute to vein graft failure. Furthermore, surgery activates innate immunity in adipose tissue, which is augmented (regionally > systemically) by LPS. Modulation of these local and distant inflammatory signaling networks stands as a potential strategy to enhance the durability of vascular interventions such as vein grafts.

Hemodialysis Graft Resistance Adjustment Device

Up to eight percent of patients develop steal syndrome after prosthetic dialysis access graft placement, which is characterized by low blood flow to the hand. Steal syndrome results in a cold hand, pain, and in extreme cases, loss of function and tissue damage. A practical and easy way of adjusting the fluidic resistance in a graft to attenuate the risk of steal physiology would greatly benefit both surgeons and patients. This paper describes the design and development of a device that can be attached to a dialysis access graft at the time of surgical implantation to enable providers to externally adjust the resistance of the graft postoperatively. Bench level flow experiments and magnetic setups were used to establish design requirements and test prototypes. The Graft Resistance Adjustment Mechanism (GRAM) can be applied to a standard graft before or after it is implanted and a non-contact magnetic coupling enables actuation through the skin for graft compression. The device features a winch-driven system to provide translational movement for a graft compression unit. We expect such a device to enable noninvasive management of steal syndrome in a manner that does not change the existing graft and support technologies, thus reducing patient complications and reducing costs to hospitals.

Abstract 481: Disturbed Flow Arterial Intimal Hyperplasia Model in the Mouse Carotid Artery Induced by a Focal Stenosis

Objective: Murine models offer a power tool for the molecular dissection of remodeling and intimal hyperplasia mechanisms, though technical challenges limit their utility. While simple, complete carotid ligation lacks direct clinical relevance, and branch outflow ligations require advanced microsurgical skills. We thus developed a simple and clinically relevant mouse model based on the hypothesis that locally disturbed flow caused by a focal high grade stenosis would yield arterial intimal hyperplasia thickening, and that the standardized diet induced obesity (DIO) model would accentuate this response.

Methods: A focal stenosis in 8 week old C57BL/6J mice (normal chow (NC, 10 kcal% fat) or DIO chow (60 kcal% fat) throughout study) was created by placing 9-0 nylon suture around the distal common carotid artery and an external 35-gauge needle (outer diameter=0.14mm), and then removing the needle to restore blood flow (∼78% reduction of lumen diameter; n=20). Tissues were perfusion fixed for morphology 4 weeks later.

Results: Both NC and DIO groups developed intimal hyperplasia proximal to the stenosis, with approximately three-times more in the DIO animals (Figure 1). Conclusions: In the mouse, a surgically created focal stenosis yields an intimal hyperplastic wall response. DIO accentuates this response. This model offers a tool for investigating mechanisms of hemodynamically driven mechanisms governing intimal hyperplasia formation.

Abstract 100: Periaortic Leptin Induces Local Medial Degeneration in ApoE -/- Mice Preceding Aneurysm Formation

Background: Leptin (Ob) is a proatherogenic hormone involved in vessel wall remodeling. We hypothesized that Ob locally synthesized in the abdominal aorta regulates vascular remodeling mediators (TGFβ, MMPs) thereby sensitizing the aorta to subsequent aneurysm formation.

Methods: Human abdominal aortic aneurysm (AAA) wall (n=10), and non-dilated aortic (n=3) samples underwent real time qPCR mRNA analysis for Ob and Ob receptor (ObR), and immunohistochemical analysis (SM-αactin, CD68, Ob, and ObR). Plasma samples obtained prior to AAA surgery were analyzed for Ob and ObR antigen (n=20). A novel mouse model was utilized to elucidate the role of Ob in AAA formation. Local Ob synthesis was simulated by point application of 20μg Ob slow release (n=10), or placebo (n=10) compound at the peri-vascular space of the para-visceral aorta in ApoE -/- mice on a Western diet. Serial ultrasound examinations on days 0, 14, 28, 35, and 42 assessed aortic diameter at reference locations. A parallel group (n=10), randomized to Ob or placebo treatment was euthanized on day 5 for aortic mRNA analysis.

Results: Increased Ob mRNA levels and immunoreactivity were evident in human AAA wall samples vs controls. Plasma Ob and ObR levels were within normal range. Ob treated mice demonstrated augmented growth rate of luminal aortic diameter in the para-visceral segment on day 28 (p=0.0001). Aortas analyzed 5 days after Ob deployment revealed suppressed TGFβ mRNA (p=0.002), while MMP-9 transcript was up-regulated (p=0.047). Ob treated mice euthanized on day 45 demonstrated localized aortic derangement of elastic fibers and loss of SM-αActin (p=0.07), alongside with increased MMP-9 (p=0.02), MMP-12 (p=0.001) antigen, and augmented adventitial macrophage infiltration.

Conclusions: Ob is locally synthesized in human AAA wall. Peri-aortic Ob modulates the vessel wall in ApoE -/- mice, inducing medial degeneration at the para-visceral region. Mechanistically, the observed derangement of ECM components was associated with suppressed TGFβ mRNA, and up-regulated MMP-9 synthesis. These data suggest novel mechanistic links between Ob and human AAA formation.

Abstract 273: Phenotypic Differences Between Human Subcutaneous and Perivascular Adipose Tissues

Objective: Human adipose lies in specific anatomic depots. Peri-vascular adipose appears unique and impacts blood vessel biology, but direct human data is limited. In view of their theorized roles, we tested the hypothesis that human peri-vascular and subcutaneous adipose tissue hold distinct phenotypic signatures. We also evaluated the impact of clinical parameters on adipose phenotype.

Methods: Fresh human peri-vascular and subcutaneous adipose tissues were collected intra-operatively from patients undergoing major lower extremity amputation (n=27) and assayed for protein levels of the adipose-associated mediators IL-6, IL-8, leptin, TNF-α, MCP-1, adiponectin, resistin and PAI-1.

Results: Leptin (2.4 fold, p=0.045) and adiponectin (1.8 fold, p=0.007) were significantly more abundant in subcutaneous compared to peri-vascular adipose (Table I). Clinical data were used to model associations between clinical characteristics and mediator levels. Age positively correlated with peri-vascular PAI-1 expression (β=0.64, p=0.042), and hyperlipidemia negatively correlated with peri-vascular adipose adiponectin (β=-1.18, p=0.039).

Conclusions: While significant similarity was observed between subcutaneous and peri-vascular adipose from leg amputation patients, the differential in adipose derived hormones leptin and adiponectin provides direct human evidence that these tissue compartments hold distinct biologic roles. Further investigation into the unique nature of peri-vascular adipose may provide meaningful guidance in managing peripheral vascular disease.

Abstract 454: Impact of Uremia on Human Adipose Phenotype

Background: Recognition of adipose-related signaling participation in vascular processes is increasing, though direct interrogation of clinically relevant human adipose has been sparse. Few scenarios rival uremia for health impact. To advance understanding of the spectrum/determinants of human adipose biology, we compared fresh extremity adipose from patients with/without uremia.

Methods: Subcutaneous adipose and clinical data was collected from patients undergoing open elective surgery. Protein was isolated, and mediator levels determined via multiplex assays.

Results: In the 71 patient cohort, mean age=63.4y; 63.3% had diabetes, 49.2% had hyperlipidemia and 53.5% had coronary disease. Compared to non-uremic patients, uremic patients had 1/10th the levels of leptin, 1/3rd the levels of adiponectin, and 3-fold higher levels of resistin (Table 1). Females had 6-fold higher leptin, 1.5-fold higher adiponectin and 2-fold higher TNF but equivalent resistin. There were no differences in mediator levels when stratified by age. In both the obese/non-obese strata, we observed a concordant pattern of association (magnitude/significance) of uremia and leptin/adiponectin/resistin. No differentials in other mediators emerged upon BMI stratification. Multiple regression analysis for leptin/adiponectin/resistin (with age/gender/uremia as independent variables) showed uremia as the highest independent predictor of all three mediators, followed by gender, whereas age had no effect.

Conclusions: Based on direct biopsy of living human adipose, uremia is associated with adiposopathy, including perturbations in the adipose derived hormones leptin, adiponectin, and resistin. Compared with other parameters including BMI, uremia overall dominated in determining adipose phenotype.

Optimal conduit choice in the absence of single-segment great saphenous vein for below-knee popliteal bypass

BACKGROUND

Single-segment great saphenous vein (SSGSV) remains the conduit of choice for femoral to below-knee popliteal (F-BK) surgical revascularization. The purpose of this study was to determine the optimal conduit in patients with inadequate SSGSV.

METHODS

This was a retrospective review of a prospectively maintained vascular registry. Patients underwent F-BK bypass with alternative vein (AV; arm vein, spliced GSV, or composite vein) or prosthetic conduit (PC).

RESULTS

From January 1995 to June 2010, 83 patients had unusable SSGSV for F-BK popliteal reconstruction. Thirty-three patients had an AV conduit and 50 had PC. The AV group was a lower median age than the PC group (69 vs 75 years). The two groups were otherwise similar in comorbid conditions of diabetes mellitus (57.6% vs 58.0%; P > .99), smoking (15.2% vs 32.0%; P = .12), and hemodialysis (3% vs 12%; P = .23). The groups were similar in baseline characteristics such as limb salvage as indication (93.9% vs 86.0%; P = .31), mean runoff score (5.2 vs 4.6; P = .39), and prior ipsilateral bypass attempts (18.2% vs 18.0%; P > .99). The AV and PC groups were also similar in 30-day mortality (6.1% vs 4.0%; P > .99) and wound infection rates (6.1% vs 6.0%; P > .99). PC patients were more likely to be discharged on Coumadin (Bristol-Myers Squibb, Princeton, NJ) than AV patients (62.0% vs 27.3%; P = .002). Seventeen of the 50 PC patients (34%) had a distal anastomotic vein cuff. A log-rank test comparison of 5-year outcomes for the AV and PC groups found no significant difference in primary patency (55.3% ± 9.9% vs 51.9% ± 10.8%; P = .82), assisted primary patency (68.8% ± 9.6% vs 54.0% ± 11.0%; P = .45), secondary patency (68.4% ± 9.6% vs 63.7% ± 10.4% for PC; P = .82), or limb salvage rates (96.2% ± 3.8% vs 81.1% ± 8.1%; P = .19). Multivariable analysis demonstrated no association between conduit type and loss of patency or limb. The factors most predictive of primary patency loss were limb salvage as the indication for surgery (hazard ratio [HR], 4.23; 95% confidence interval [CI], 1.65-10.9; P = .003) and current hemodialysis (HR, 3.51; 95% CI, 1.08-11.4; P = .037). The most predictive factor of limb loss was current hemodialysis (HR, 7.02; 95% CI, 1.13-43.4; P = .036).

CONCLUSIONS

For patients with inadequate SSGSV, PCs, with varying degrees of medical and surgical adjuncts, appear comparable to AV sources in graft patency for below-knee popliteal bypass targets. This observation is tempered by the small cohort sample size of this single-institutional analysis. Critical limb ischemia as the operative indication and current hemodialysis predict impaired patency, and hemodialysis is associated with limb loss.

Mouse vein graft hemodynamic manipulations to enhance experimental utility

Mouse models serve as a tool to study vein graft failure. However, in wild-type mice, there is limited intimal hyperplasia, hampering efforts to identify anti-intimal hyperplasia therapies. Furthermore, vein graft wall remodeling has not been well quantified in mice. We hypothesized that simple hemodynamic manipulations can reproducibly augment intimal hyperplasia and remodeling end points in mouse vein grafts, thereby enhancing their experimental utility. Mouse inferior vena cava-to-carotid interposition isografts were completed using an anastomotic cuff technique. Three flow restriction manipulations were executed by ligating outflow carotid branches, creating an outflow common carotid stenosis, and constructing a midgraft stenosis. Flowmetry and ultrasonography were used perioperatively and at day 28. All ligation strategies decreased the graft flow rate and wall shear stress. Morphometry showed that intimal thickness increased by 26% via carotid branch ligation and by 80% via common carotid stenosis. Despite similar mean flow rates and shear stresses among the three manipulations, the flow waveform amplitudes were lowest with common carotid stenosis. The disordered flow of the midgraft stenosis yielded poststenotic dilatation. The creation of an outflow common carotid stenosis generates clinically relevant (poor runoff) vein graft low wall shear stress and offers a technically flexible method for enhancing the intimal hyperplasia response. Midgraft stenosis exhibits poststenotic positive wall remodeling. These reproducible approaches offer novel strategies for increasing the utility of mouse vein graft models.

Immobilization of iron oxide magnetic nanoparticles for enhancement of vessel wall magnetic resonance imaging--an ex vivo feasibility study

Emerging data supports a role for negative wall remodeling in the failure of vascular interventions such as vein grafts, yet clinicians/researchers currently lack the ability to temporally/efficiently investigate adventitial surface topography/total vascular wall anatomy in vivo. We established a strategy of immobilizing commercially available iron oxide magnetic nanoparticles (Fe-NPs) onto the surface of human vein conduits to facilitate high-throughput total vascular wall demarcation with magnetic resonance (MR). Binding of activated Fe-NPs to amine groups on the surface of the veins induced a thin layer of negative contrast that differentiated the adventitia from surrounding saline signal in all MR images, enabling delineation of total wall anatomy; this was not possible in simultaneously imaged unlabeled control veins. Under the conditions of this ex vivo experiment, stable covalent binding of Fe-NPs can be achieved (dose-dependent) on human vein surface for MR detection, suggesting a potential strategy for enhancing the ability of MRI to investigate total wall adaptation and remodeling in vein graft failure.

Emerging data supports a role for negative wall remodeling in the failure of vascular interventions such as vein grafts, yet clinicians/researchers currently lack the ability to temporally/efficiently investigate adventitial surface topography/total vascular wall anatomy in vivo. We established a strategy of immobilizing commercially available iron oxide magnetic nanoparticles (Fe-NPs) onto the surface of human vein conduits to facilitate high-throughput total vascular wall demarcation with magnetic resonance (MR).

Immobilized contrast-enhanced MRI: Gadolinium-based long-term MR contrast enhancement of the vein graft vessel wall

An implantable MR contrast agent that can be covalently immobilized on tissue during surgery has been developed. The rationale is that a durable increase in tissue contrast using an implantable contrast agent can enhance postsurgical tissue differentiation using MRI. For small-vessel (e.g., vein graft) MRI, the direct benefit of such permanent "labeling" of the vessel wall by modification of its relaxation properties is to achieve more efficient imaging. This efficiency can be realized as either increased contrast leading to more accurate delineation of vessel wall and lesion tissue boundaries, or, faster imaging without penalizing contrast-to-noise ratio, or a combination thereof. We demonstrate, for the first time, stable long-term MRI enhancement using such an exogenous contrast mechanism based on immobilizing a modified diethylenetriaminepentaacetic acid gadolinium(3+) dihydrogen complex on a human vein using a covalent amide bond. Signal enhancement due to the covalently immobilized contrast agent is demonstrated for excised human vein specimens imaged at 3 T, and its long-term stability is demonstrated during a 4-month incubation period.

Interplay of CCR2 signaling and local shear force determines vein graft neointimal hyperplasia in vivo

Leukocytes play a central role in vein graft neointimal hyperplasia, which is significantly augmented under low shear conditions. The current concept is that shear force regulates leukocyte adhesion predominately through up-regulation of chemokines and growth factors within the graft wall. Using rabbit and murine vein graft models, we demonstrate that CC chemokine receptor 2/monocyte chemoattractant protein-1 mediated monocyte recruitment and a low shear environment act synergistically to augment neointimal hyperplasia development and removal of either of the conditions leads to a significant reduction in neointimal thickening. We propose a novel concept that the shear stress response element phenotypically stems from the complex interplay of the biological and physical microenvironments.

Established neointimal hyperplasia in vein grafts expands via TGF-beta-mediated progressive fibrosis

In weeks to months following implantation, neointimal hyperplasia (NIH) in vein grafts (VGs) transitions from a cellularized to a decellularized phenotype. The inhibition of early cellular proliferation failed to improve long-term VG patency. We have previously demonstrated that transforming growth factor-beta(1) (TGF-beta(1))/connective tissue growth factor (CTGF) pathways mediate a conversion of fibroblasts to myofibroblasts in the early VG (<2 wk). We hypothesize that these similar pathways drive fibrosis observed in the late VG lesion. Within rabbit VGs, real-time RT-PCR, Western blot analysis, ELISA, and immunohistochemistry were used to examine TGF-beta/CTGF pathways in late (1-6 mo) NIH. All VGs exhibited a steady NIH growth (P = 0.006) with significant reduction in cellularity (P = 0.01) over time. Substantial TGF-beta profibrotic activities, as evidenced by enhanced TGF-beta(1) activation, TGF-beta receptor types I (activin receptor-like kinase 5)-to-II receptor ratio, SMAD2/3 phosphorylation, and CTGF production, persisted throughout the observation period. An increased matrix synthesis was accompanied by a temporal reduction of matrix metalloproteinase-2 (P = 0.001) and -9 (P < 0.001) activity. VG NIH is characterized by a conversion from a proproliferative to a profibrotic morphology. An enhanced signaling via TGF-beta/CTGF coupled with reduced matrix metalloproteinase activities promotes progressive fibrotic NIH expansion. The modulation of late TGF-beta/CTGF signaling may offer a novel therapeutic strategy to improve the long-term VG durability.

An experiment-based model of vein graft remodeling induced by shear stress

Vein graft intimal hyperplasia induced by shear stress is considered to be one of the major causes of vein graft failure. We have developed a mathematical model of vein graft intimal hyperplasia induced by shear stress based on experimental data. Intimal thickness and the rate of intimal thickness change are expressed as functions of shear stress and time. The model coefficients are derived from animal experiments where bilateral rabbit carotid vein grafts are exposed to different shear stress levels. Morphology data of the vein grafts are obtained over multiple time points. The model describes the well-known behavior of intimal thickening, which is inversely related to shear stress. It also depicts the time-dependent behavior of vein graft intimal hyperplasia. Finally, the model is used to simulate the intimal growth around a focal stenosis, which was created by ligating the middle of a vein graft using a suture. Simulation results and experimental data agree qualitatively, and demonstrate that the intima thickens more distal to the stenosed area. These experiments establish the potential of the general experiment-based approach for predicting human vein graft remodeling. Other mechanical and biological factors can be included following a similar approach in order to obtain a more accurate vein graft remodeling model.

A model of vein graft intimal hyperplasia

When vein graft is implanted in the arterial system, the vein graft wall becomes thicker as an adaptive process. We have developed a model of early adaptive vein graft intimal thickening induced by shear stress. Intimal thickness and the rate of intimal thickening are expressed as functions of shear stress and time based on experimental data. The model describes the behavior of intimal thickening which is inversely related to shear stress. It also depicts the time-dependent behavior of the vein graft intimal thickening.

Impact of an Absorbent Silver-Eluting Dressing System on Lower Extremity Revascularization Wound Complications

Surgical wounds for lower extremity revascularization are prone to infection and dehiscence. Acticoat Absorbent, an antimicrobial dressing, offers sustained release of ionic silver. We hypothesized that immediate application of Acticoat as a postoperative dressing would reduce wound complications in patients undergoing leg revascularization. All infrainguinal revascularization cases involving leg incisions at a single Veterans Administration Medical Center were identified from July 1, 2002, to September 30, 2005. The control group received conventional dressings, while the treatment group received an Acticoat dressing. Wound complication rates were captured via National Surgical Quality Improvement Program data. Patient characteristics and procedure distributions were similar between groups. The wound complication rate fell 64% with utilization of the Acticoat-based dressing (control 14% [17/118], treatment 5% [7/130]; P = 0.016). An Acticoat-based dressing system offers a potentially useful, cost-effective adjunct to reduce open surgical leg revascularization wound complications.

Cytokines and the early vein graft: strategies to enhance durability

This brief review focuses on experimental studies linking the proinflammatory cytokine tumor necrosis factor-alpha to accelerated vein graft failure in the broader historical context of vein graft research. From some perspectives, the field appears ripe for transfer of cytokine knowledge and therapeutic approaches that have evolved in other systems to vascular surgery problems. However, the complexity of vein graft disease suggests that more robust research approaches, such as broadening of the scope beyond focus on single mediators and neointimal hyperplasia, will be necessary to reach translatable strategies to prolong human vein graft durability.

TNF-alpha and shear stress-induced large artery adaptations

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) up-regulation has been associated with both low and high shear-induced arterial remodeling. To address this apparent paradox and to define the biology of TNF-alpha signaling in large arteries, we tested the hypotheses that differential temporal expression of TNF-alpha drives shear-regulated arterial remodeling.

MATERIALS AND METHODS

Both low- and high-shear environments in the same rabbit were surgically created for common carotid arteries. Common carotid arteries (n = 60 total) were harvested after d0, d1, d3, d7, and d14 and analyses included morphology, TNF-alpha, and IL-10 mRNA quantitation. In separate experiments, animals received pegylated soluble TNF-alpha Type 1 receptor (PEG sTNF-RI) or vehicle via either short- or long-term dosing to define the effect of TNF-alpha blockade.

RESULTS

The model yielded a 14-fold shear differential (P < 0.001) with medial thickening under low shear (P = 0.025), and evidence of outward remodeling with high shear (P = 0.007). Low shear immediately up-regulated TNF-alpha expression approximately 50 fold (P < 0.001) at d1. Conversely, high shear-induced delayed and sustained TNF-alpha expression (22-fold at d7, P = 0.012; 23-fold at d14, P = 0.007). Both low and high shear gradually induced IL-10 expression (P = 0.002 and P = 0.004, respectively). Neither short-term (5-day) nor long-term (14-day) blockage of TNF-alpha signaling resulted in treatment-induced changes in the remodeling of low- or high-shear arteries.

CONCLUSIONS

Shear stress differentially and temporally regulates TNF-alpha expression in remodeling large arteries. However, TNF-alpha blockage did not substantially impact the final shear-induced morphology, suggesting that large arteries can remodel in response to flow perturbations independent of TNF-alpha signaling.

TGF-beta- and CTGF-mediated fibroblast recruitment influences early outward vein graft remodeling

Luminal shearing forces have been shown to impact both geometric remodeling and the development of intimal hyperplasia. Less well studied is the influence of intramural wall stresses on vessel growth and adaptation. Using a vein graft-fistula configuration to isolate the impact of circumferential wall stress, we identify the reorganization of adventitial myofibroblasts as the dominant histological event that limits early outward remodeling of vein grafts in response to elevated wall stress. We hypothesize that increased production of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) induces recruitment of myofibroblasts, promotes adventitial reorganization, and limits early outward remodeling in response to increased intramural wall stress. Vein grafts with a distal arteriovenous fistula in the neck of rabbits were constructed, resulting in a fourfold differential in circumferential wall stress. Using this model, we demonstrate 1) elevated wall stress augments the production of TGF-beta and CTGF, 2) increased TGF-beta expression and CTGF expression are correlated with the enhanced differentiation from fibroblasts to myofibroblasts, as evidenced by the significant increase in the alpha-actin-positive cells in adventitia, and 3) the levels of TGF-beta, CTGF, and alpha-actin are inversely correlated with the magnitude of outward remodeling of the graft wall. Increased wall stress after vein graft implantation appears to induce a TGF-beta- and CTGF-mediated recruitment of adventitial fibroblasts and a conversion to a myofibroblast phenotype. Although important in the maintenance of wall stability in the face of an increased mechanical load, this adventitial adaptation limits early outward remodeling of the vein conduit and may prove deleterious in maintaining long-term vein graft patency.

Reduction of iron stores and cardiovascular outcomes in patients with peripheral arterial disease: a randomized controlled trial

CONTEXT

Accumulation of iron in excess of physiologic requirements has been implicated in risk of cardiovascular disease because of increased iron-catalyzed free radical-mediated oxidative stress.

OBJECTIVE

To test the hypothesis that reducing body iron stores through phlebotomy will influence clinical outcomes in a cohort of patients with symptomatic peripheral arterial disease (PAD).

DESIGN, SETTING, AND PATIENTS

Multicenter, randomized, controlled, single-blinded clinical trial based on the Iron (Fe) and Atherosclerosis Study (FeAST) (VA Cooperative Study #410) and conducted between May 1, 1999, and April 30, 2005, within the Department of Veterans Affairs Cooperative Studies Program and enrolling 1277 patients with symptomatic but stable PAD. Those with conditions likely to cause acute-phase increase of the ferritin level or with a diagnosis of visceral malignancy within the preceding 5 years were excluded. Analysis was by intent-to-treat.

INTERVENTION

Patients were assigned to a control group (n = 641) or to a group undergoing reduction of iron stores by phlebotomy with removal of defined volumes of blood at 6-month intervals (avoiding iron deficiency) (n = 636), stratified by hospital, age, and baseline smoking status, diagnosis of diabetes mellitus, ratio of high-density to low-density lipoprotein cholesterol level, and ferritin level.

MAIN OUTCOME MEASURES

The primary end point was all-cause mortality; the secondary end point was death plus nonfatal myocardial infarction and stroke.

RESULTS

There were no significant differences between treatment groups for the primary or secondary study end points. All-cause deaths occurred in 148 patients (23%) in the control group and in 125 (20%) in the iron-reduction group (hazard ratio (HR), 0.85; 95% confidence interval (CI), 0.67-1.08; P = .17). Death plus nonfatal myocardial infarction and stroke occurred in 205 patients (32%) in the control group and in 180 (28%) in the iron-reduction group (HR, 0.88; 95% CI, 0.72-1.07; P = .20).

CONCLUSION

Reduction of body iron stores in patients with symptomatic PAD did not significantly decrease all-cause mortality or death plus nonfatal myocardial infarction and stroke.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT00032357.

Tumor necrosis factor-alpha and the early vein graft

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) has been implicated in the blood vessel wall response to hemodynamic forces. We hypothesized that TNF-alpha activity drives neointimal hyperplasia (NIH) during vein graft arterialization and that anti-TNF-alpha therapy would inhibit NIH.

METHODS

Rabbits underwent bilateral vein grafting using jugular vein. All distal branches except the occipital artery were unilaterally ligated to create distinct flow environments between the bilateral grafts. Vein grafts were harvested sequentially up to 28 days for TNF-alpha messenger RNA (mRNA) quantitation. In separate experiments, animals received short-term or long-term dosing with pegylated soluble TNF-alpha type I receptor (PEG sTNF-RI) or vehicle. After 14 to 28 days, grafts were analyzed for morphometry, proliferation, apoptosis, and PEG sTNF-RI distribution.

RESULTS

Quantitative mRNA assay (TaqMan) revealed shear-dependent (P < .001) and time-dependent (P < .001) TNF-alpha expression. TNF-alpha induction was maximal at day 1 and gradually decreased over time, but was persistently elevated even 4 weeks later (P < .001). Low shear (associated with increased NIH) resulted in significantly higher TNF-alpha mRNA expression (P = .03). PEG sTNF-RI was found in high concentrations in the serum and localized to NIH. The high-flow and low-flow vein grafts from treated animals demonstrated similar volumes of NIH compared with controls. PEG-sTNF-RI had only modest impact on vascular wall cell turnover, as reflected by terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling (P = .064) and anti-Ki-67 (P = .12) assays.

CONCLUSIONS

Placement of a vein into the arterial circulation acutely upregulates TNF-alpha; this expression level correlates with the degree of subsequent NIH. Pharmacologic interruption of this signaling pathway has no significant impact on NIH or wall cellular proliferation/apoptosis, suggesting that early vein graft adaptations can proceed via TNF-alpha-independent mechanisms.

Clinical outcomes after closed, staged, and open forefoot amputations

BACKGROUND

Surgical approaches for forefoot osteomyelitis include amputation with immediate wound closure or resection followed by either staged re-resection and wound closure or local care of the open wound for secondary healing. This study evaluated the effectiveness of closed, staged, and open forefoot amputations in preventing major leg amputation and identified those variables that are associated with successful limb preservation.

METHODS

From July 2002 to June 2004, 208 patients with forefoot osteomyelitis or gangrene underwent minor amputation according to a standard treatment algorithm. Wounds with limited cellulitis underwent immediate wound closure (CLOSED), wounds with marginally viable soft tissue underwent open amputation followed by wound closure at 2 to 7 days (STAGED), and wounds with tenosynovitis or extensive necrosis underwent débridement with no attempt at wound closure (OPEN). Patient demographics, need for further operative interventions, time to complete healing, and progression to major amputation were recorded.

RESULTS

With four subjects lost to follow-up, 204 patients (98%) (94 CLOSED, 56 STAGED, and 54 OPEN) were monitored to complete healing, major amputation, or death. OPEN amputations had a significantly reduced initial healing rate (37%, P < .001) and a frequent need for repeat operative intervention (43%), although successful limb salvage was ultimately achieved in 70% of the cases. Initial healing in the CLOSED and STAGED amputation groups was similar (71% and 78%, respectively), leading to excellent early limb salvage (86% and 91%). The median time to healing for closed, staged, and open amputations was 1.2, 1.6, and 4.6 months, respectively (P < .001). Follow-up evaluation demonstrated the initial improvements in limb salvage with the CLOSED and STAGED groups were lost, resulting in similar amputation rates among the three groups of 30% to 35% over 36 months.

CONCLUSIONS

Although open amputation of extensive forefoot infections frequently requires repeat operative interventions and a prolonged time to complete healing, this approach provides limb salvage rates approaching those observed for less invasive infections amenable to immediate closure. Staged closure offers an improved time to healing without negatively impacting the risk of major limb amputation. Independent of their initial operative approach, these patients frequently progress to early leg amputation.

Early Differential MMP-2 and -9 Dynamics During Flow-Induced Arterial and Vein Graft Adaptations

BACKGROUND

Arteries and vein grafts respond differently to reductions in flow, with arteries demonstrating inward remodeling through only limited structural reorganization of the media and vein grafts developing a thickened intima, with little change in the external diameter. In an effort to mechanistically explore the biology of this contrasting behavior, we hypothesized that this differential response in flow-mediated remodeling is driven by unique temporal expression patterns and functional activities of the matrix metalloproteinase (MMP)-2 and -9, key effectors of blood vessel architecture remodeling.

MATERIAL AND METHODS

In rabbits, bilateral carotid vein grafting was coupled with unilateral partial distal ligation to create a sevenfold flow differential between sides. Vein grafts and proximal carotid arteries were then harvested for morphological and biochemical studies at time points ranging from 1 to 14 days.

RESULTS

Vein grafts demonstrated an early, transient increase in pro-MMP-9 within adherent monocytes and endothelial cells. This was followed by a delayed increase in smooth muscle cell active MMP-2, which was coincident with the onset of intimal thickening at days 7 and 14 and significantly elevated by low flow. In contrast, arteries showed no elevation in pro MMP-9 above baseline, but demonstrated a transient increase in latent MMP-2 preceding the flow-mediated change in vessel diameter.

CONCLUSIONS

These data provide evidence for unique and independent roles of MMP-2 and -9 in the process of hemodynamically driven vascular remodeling.

Anti-tumor necrosis factor-{alpha} therapies attenuate adaptive arteriogenesis in the rabbit

The specific antagonists of tumor necrosis factor-alpha (TNF-alpha), infliximab and etanercept, are established therapeutic agents for inflammatory diseases such as rheumatoid arthritis and Crohn's disease. Although the importance of TNF-alpha in chronic inflammatory diseases is well established, little is known about its implications in the cardiovascular system. Because proliferation of arteriolar connections toward functional collateral arteries (arteriogenesis) is an inflammatory-like process, we tested in vivo the hypothesis that infliximab and etanercept have antiarteriogenic actions. Sixty-three New Zealand White rabbits underwent femoral artery occlusion and received infliximab, etanercept, or vehicle according to clinical dosage regimes. After 1 wk, collateral conductance, assessed with fluorescent microspheres, revealed significant inhibition of arteriogenesis (collateral conductance): 52.4 (SD 8.1), 35.2 (SD 7.7), and 33.3 (SD 10.1) ml x min(-1) x 100 mmHg(-1) with PBS, infliximab, and etanercept, respectively (P < 0.001). High-resolution angiography showed no significant differences in number of collateral arteries, but immunohistochemical analysis demonstrated a decrease in mean collateral diameter, proliferation of vascular smooth muscle cells, and reduction of leukocyte accumulation around collateral arteries in treated groups. Infliximab and etanercept bound to infiltrating leukocytes, which are important mediators of arteriogenesis. Infliximab induced monocyte apoptosis, and neither substance affected monocyte expression of the adhesion molecule Mac-1. We demonstrated that TNF-alpha serves as a pivotal modulator of arteriogenesis, which is attenuated by treatment with TNF-alpha inhibitors. Reduction of collateral conductance is most likely due to inhibition of perivascular leukocyte infiltration and subsequent lower vascular smooth muscle cell proliferation. This is the first report showing a negative influence of TNF-alpha inhibitors on collateral artery growth.

Impact of Shear Stress on Early Vein Graft Remodeling: A Biomechanical Analysis

In this study, an analytical technique was developed to estimate the dynamic, three-dimensional wall shear and tensile forces within the arterial circulation and applied to our established model of flow-mediated graft remodeling within the rabbit carotid system. Through selective unilateral distal ligation, vein grafts were exposed to distinct flow environments, characterized by a sixfold difference in mean flow rate. Implanted vein grafts were harvested at 1, 3, 7, 14, and 28 days to evaluate graft morphology. Hemodynamic and real-time imaging data, obtained at graft implantation and harvest, served as input for estimation of dynamic shear stress and wall tension. Marked differences in the remodeling process were observed in high vs. low flow grafts, with low flow grafts demonstrating accelerated intimal hyperplasia and reduced outward remodeling. The impact was a peak in the maximum and minimum shear stress at Day 7, with a delayed increase in lumen diameter leading to partial normalization of the wall shear by Day 28. Intramural wall tension reached a maximum at Day 3, with an increase in wall thickness leading to a significant reduction in these forces by Day 14. Despite the significant morphologic changes, no differences in the incremental moduli of elasticity were observed.

Altered rheology of lymphocytes in the diabetic mouse

AIMS/HYPOTHESIS

Clinical complications associated with diabetes may be related to altered physical properties of leucocytes. We used micropipette techniques to examine leucocyte rheology (specifically lymphocyte rheology) in the non-obese diabetic (NOD) mouse model of diabetes mellitus. We hypothesised that diabetes affects lymphocyte rheology, and specifically that lymphocyte membranes from diabetic mammals have a higher cortical tension than those from non-diabetic mammals.

METHODS

Lymphocytes were isolated from diabetic and control mice. Lymphocyte deformation and activation were assessed with a micropipette apparatus. Cellular activation was assessed visually. Projection length into the micropipette during aspiration was used to calculate the viscosity of the cell. Recovery length following expulsion from the micropipette was used to derive the recovery time constant, which is the ratio of cortical tension : viscosity (T(o)/mu) for each cell. The cell cortical/surface tension was calculated from this ratio.

RESULTS

Of 692 control lymphocytes, 29% were spontaneously activated compared with 39% of 624 diabetic cells (p<0.06) and 31.5% of 315 non-diabetic NOD cells (p=0.14). Viscosity values for diabetic lymphocytes were equivalent to those for control cells (1345.12+/-1420.97 Pa.s vs 996.84+/-585.07 Pa.s, p=0.13). The average T(o)/micro value for diabetic lymphocytes (35.4+/-16.5x10(-6) cm/s) was significantly higher than that for control cells (24.8+/-11.3x10(-6) cm/s, p<0.03) and cells from non-diabetic NOD mice (26.3+/-9.0x10(-6) cm/s, p<0.005). The mean cortical tension values for diabetic and control cells were 4.7+/-2.3x10(-4) N/m and 2.8+/-0.7x10(-4) N/m respectively (p<0.003).

CONCLUSIONS/INTERPRETATION

Lymphocytes from diabetic mice tend to spontaneously activate. They have an equivalent cytoplasmic viscosity but a larger recovery time constant compared with cells from control mice. The results suggest that diabetic lymphocytes are stiffer than control cells.

Wall shear modulation of cytokines in early vein grafts

OBJECTIVE

Pro-inflammatory cytokine-driven mechanisms have been implicated in vein graft failure, though little is known about the effect of hemodynamic factors and anti-inflammatory counter-regulatory mechanisms. We hypothesized that early temporal expression of the pro-inflammatory cytokine interleukin (IL)-1 beta and the anti-inflammatory cytokine IL-10 proceeds by way of wall shear stress-dependent pathways in the arterializing vein graft.

METHODS

Rabbits (n = 27) underwent bilateral jugular vein carotid interposition grafts, and simultaneous unilateral distal carotid branch ligation, to produce both low-flow and high-flow grafts in the same animal. Vein grafts were harvested at 1, 3, 7, 14, and 28 days and were assessed for architecture, wall shear stress, and cytokine messenger RNA levels (quantitative real-time two-step reverse transcription polymerase chain reaction).

RESULTS

The model resulted in an immediate 90% flow reduction (P <.001, paired t test) in the vein graft on the ligated side, and a 36% increase (P =.01) in contralateral graft flow. This persisted as approximately 15-fold flow differential throughout the 28-day period. The construction yielded a 15-fold differential in wall shear stress between low-flow and high-flow vein grafts (P <.001, two-way repeated measures analysis of variance). Intimal hyperplasia began by day 3, and was 6-fold more in low wall shear grafts by 28 days (230.6 +/- 35.4 microm intimal thickness vs 36.1 +/- 17.6 microm for low shear versus high shear grafts; P =.001). For both cytokines time independently affected mRNA expression (P <.001, global analysis of variance). Exposure of vein grafts to the arterial circulation markedly up-regulated IL-1 beta at 1 day, with significantly more induction in the low shear setting (P =.002). IL-1 beta protein localized to the developing neointima at days 1 and 3. Conversely, IL-10 slowly increased until day 14, with significantly more expression in the high shear grafts (P <.001).

CONCLUSIONS

Vein graft adaptation induces early pro-inflammatory cytokine IL-1 beta expression and delayed protective IL-10 expression (most notable under high shear conditions), both of which are modulated by wall shear. These differential temporal windows offer strategies for appropriately timed pro-inflammatory or anti-inflammatory therapies to interrupt pathologic vein graft adaptations.

CLINICAL RELEVANCE

Neointimal hyperplasia continues to limit the durability of vein bypass grafts. Emerging evidence suggests that inflammatory mechanisms drive the neointimal hyperplasic response. This study demonstrates that specific hemodynamic forces (altered wall shear stress) differentially affect early pro-inflammatory interleukin (IL)-1 beta and delayed anti-inflammatory IL-10 signaling. These distinct temporal windows for IL-1 beta and IL-10 cytokine expression offer strategies for appropriately timed pro-inflammatory and anti-inflammatory therapies to interrupt pathologic vein graft adaptations.

Impact of IL-1β on flow-induced outward arterial remodeling

BACKGROUND

Flow reduction upregulates arterial wall interleukin 1beta (IL-1beta), and IL-1beta independently modulates intimal hyperplasia under low flow conditions. We hypothesized that IL-1beta expression is also augmented under high flow, and outward remodeling occurs by way of IL-1beta-dependent mechanisms.

METHODS

Carotid artery (CA) flow was surgically augmented in rabbits (n = 20). CAs were harvested at 1, 3, 7, and 14 days, and assayed via quantitative reverse transcriptase-polymerase chain reaction. IL-1 receptor I null mice (KO) and wild-type controls underwent unilateral CA ligation and harvest 4 weeks later to assess the impact of increased flow on the contralateral CA (n = 82).

RESULTS

The rabbit model led to an immediate 36% increase in contralateral flow (P = .01) with an 80% increase at 14 days (P = .016) with subsequent positive remodeling. High flow induced IL-1beta messenger RNA expression (114-fold at 1 day, P < .05), with levels remaining elevated through 14 days (61-fold, P < .05). In murine experiments, CA ligation resulted in a 44% increase in contralateral flow. Wild-type and KO animals responded with equivalent 83% and 78% increases in luminal area (P = .87).

CONCLUSIONS

Positive and negative perturbations of arterial blood flow induce IL-1beta in a time-dependent fashion. However, as opposed to intimal hyperplasia after flow reduction, positive arterial remodeling in response to increased flow occurs via IL-1beta independent mechanisms.

Differential expression and activity of matrix metalloproteinases during flow-modulated vein graft remodeling

OBJECTIVE

While shear stress closely regulates vascular remodeling, the mediators of this process have been only partially elucidated. The current study examined the role of the gelatinases in flow-mediated vein graft intimal hyperplasia. We hypothesized that matrix metalloproteinase (MMP)-2 and MMP-9 expression and protein levels, relative to tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2, are upregulated in a flow-dependent manner during vein graft arterialization.

METHODS

Bilateral common carotid interposition vein grafting was performed in rabbits. Reduction in flow was achieved through unilateral ligation of the internal carotid artery and three of four branches of the external carotid artery. At 28 days grafts were harvested and analyzed for intimal area; MMP-2 and MMP-9, and TIMP-1 and TIMP-2 messenger RNA content, via quantitative reverse transcription polymerase chain reaction; and MMP-2 and MMP-9, and TIMP-1 and TIMP-2 protein concentrations, via both bioactivity assay and zymography.

RESULTS

Branch ligation resulted in a 10-fold difference in mean flow rate and accelerated development of intimal hyperplasia in a low-flow environment. Exposure of the vein graft to arterial hemodynamics induced a marked rise in MMP-9 mRNA levels, whereas only a modest increase in MMP-2 mRNA was observed. MMP-2 protein was 50 to 100 times more abundant than MMP-9, and was significantly upregulated in grafts that demonstrated enhanced intimal thickening. Immunohistochemistry demonstrated that MMP-2 was located throughout the myointima, whereas MMP-9 was localized almost exclusively to the region of endothelium. No differences in TIMP-1 and TIMP-2 mRNA or protein levels were detected between high-flow and low-flow grafts.

CONCLUSION

MMP-2 is the predominate gelatinase that regulates early vein graft remodeling. Despite a marked increase in MMP-9 gene expression, development of intimal hyperplasia after a reduction in wall shear rate correlates with an increase in MMP-2 protein levels. These data suggest differential regulatory mechanisms for proteases within the remodeling vein graft wall. Modulation of extracellular matrix biologic features may offer therapeutic strategies for the prevention of vein graft failure.

Arteriogenesis proceeds via ICAM-1/Mac-1- mediated mechanisms

Monocyte adhesion to shear stress-activated endothelium stands as an important initial step during arteriogenesis (collateral artery growth). Using multiple approaches, we tested the hypothesis that monocyte adhesion via intercellular adhesion molecule-1 (ICAM-1) and selectin interactions is essential for adaptive arteriogenesis. Forty-eight New Zealand White rabbits received either solvent, monocyte chemoattractant protein-1 (MCP-1) alone, MCP-1 plus ICAM-mab, or MCP-1 plus an IgG2a isotype control via osmotic minipumps. After 7 days, collateral conductance was evaluated: solvent 4.01 (mL/min per 100 mm Hg), MCP-1 plus ICAM-mab 8.04 (versus solvent P=NS), and MCP-1 alone 33.11 (versus solvent P<0.05). Furthermore, the right femoral arteries of ICAM-1-/-, Mac-1-/- and mice having defective selectin interactions (FT4/7-/-) as well as their corresponding controls were ligated. One week later, perfusion ratios were determined by the use of fluorescent microspheres. FT4/7-/- mice did not show any significant difference in perfusion restoration whereas ICAM-1-/- and Mac-1-/- mice had a significant reduction in arteriogenesis as compared with matching controls (FT4/7-WT 37+/-9%, FT4/7-/- 32+/-3%, P=0.31; C57BL/6J 59+/-9%, ICAM-1-/- 36+/-8%, P<0.05; Mac-1-/- 42+/-3%, P<0.05). ICAM-1/Mac-1-mediated monocyte adhesion to the endothelium of collateral arteries is an essential step for arteriogenesis, whereas this process can proceed via selectin interaction independent mechanisms. Furthermore, in vivo treatment with monoclonal antibodies against ICAM-1 totally abolishes the stimulatory effect of MCP-1 on collateral artery growth, suggesting that the mechanism of the MCP-1-induced arteriogenesis proceeds via the localization of monocytes rather than the action of the MCP-1 molecule itself.

A novel vein graft model: adaptation to differential flow environments

Accelerated intimal hyperplasia in response to altered flow environment is critical to the process of vein bypass graft failure. Lack of a reproducible animal model for dissecting the mechanisms of vein graft (VG) remodeling has limited progress toward solving this clinically significant problem. Combining a cuffed anastomotic technique with other surgical manipulations, we developed a well-defined, more robust method for studying hemodynamic factors in VG arterialization. VG with fistula placement, complete occlusion, or partial distal branch ligation (DBL) was performed in the carotid artery of 56 rabbits. Extensive hemodynamic and physiological analyses were performed to define the hemodynamic forces and histological adaptations of the wall at 1-28 days. Anastomotic time averaged 12 min, with 100% patency of bilateral grafts and unilateral grafts plus no adjunct or delayed fistula. Bilateral VG-DBL resulted in an immediate disparity in wall shear (0.8 +/- 0.1 vs. 12.4 +/- 1.1 dyn/cm2, ligated vs. contralateral graft). Grafts exposed to low shear stress responded primarily through enhanced intimal thickening (231 +/- 35 vs. 36 +/- 18 microm, low vs. high shear). High-shear-stress grafts adapted through enhanced outward remodeling, with a 24% increase in lumen diameter at 28 days (3.0 +/- 0.1 vs. 3.7 +/- 0.2 mm, low vs. high shear). We have taken advantage of the cuffed anastomotic technique and combined it with a bilateral VG-DBL model to dissect the impact of hemodynamic forces on VG arterialization. This novel model offers a robust, clinically relevant, statistically powerful small animal model for evaluation of high- and low-shear-regulated VG remodeling.

Morbidity with retroperitoneal procedures during endovascular abdominal aortic aneurysm repair

PURPOSE

Retroperitoneal iliac procedures can enable successful endovascular repair of abdominal aortic aneurysm (AAA) in patients who otherwise would not be anatomically eligible. The purpose of this study was to determine perioperative outcome with adjunctive retroperitoneal procedures compared with standard bilateral femoral exposure.

METHODS

Between August 1997 and November 2002, 164 patients underwent elective endovascular AAA repair at a single university medical center. Anatomic, demographic, and early postoperative outcome data gathered prospectively were analyzed. Thirty-two patients (20%) underwent 38 separate adjunctive retroperitoneal procedures. Indications included small external iliac arteries (16 of 32 patients; 50%) and concomitant iliac aneurysm that precluded fixation of the endograft limbs in the common iliac arteries (16 of 32 patients; 50%). The 38 procedures consisted of 8 iliac conduits only, 14 iliac conduits with iliofemoral bypass grafts, and 16 hypogastric revascularization procedures. Data for the study patients were compared with data for 132 patients who underwent endovascular AAA repair through femoral incisions. Primary end points were hospital length of stay, and early morbidity and mortality.

RESULTS

Retroperitoneal procedures enabled an additional 14% of patients with AAA to undergo endovascular techniques. However, there was a significantly higher proportion of women and patients at high risk for anesthesia (American Society of Anesthesiologists class IV or higher) in the group who underwent retroperitoneal procedures. On average, retroperitoneal procedures were associated with 2.6-fold greater blood loss, 82% longer procedure time, 1.5 days additional hospital stay, and 1.8-fold higher rate of perioperative complications, compared with endovascular AAA repair with femoral exposure alone. In contrast, early mortality was similar in the two groups.

CONCLUSION

Adjunctive retroperitoneal procedures during endovascular AAA repair are associated with increased risk for complications and longer hospital length of stay, compared with AAA repair with standard femoral exposure only. They do not, however, increase early mortality, even in patients at high risk, and enable a larger subset of patients with AAA to undergo endovascular repair.

Prospective validation of an algorithm to maximize native arteriovenous fistulae for chronic hemodialysis access

OBJECTIVE

The purpose of this study was to evaluate an algorithm to maximize native arteriovenous fistulae (AVF) for hemodialysis access.

METHODS

The prospective study design was set in an academic, tertiary care medical center. The study subjects were adults referred for permanent, upper extremity hemodialysis access between April 1999 and May 2001. Intervention included Doppler arterial pressures/waveforms and duplex imaging of the basilic, cephalic, and central veins. The optimal configuration for an AVF was determined (criteria: vein >3 mm, no arterial inflow stenosis, no venous outflow stenosis) on the basis of the noninvasive studies, and unilateral arteriography/venography was performed to confirm the choice. Permanent hemodialysis access was created on the basis of the imaging studies, and remedial imaging/intervention was performed if the AVF failed to mature. Outcome measures included impact of the noninvasive/invasive imaging, perioperative morbidity/mortality, incidence of successful AVF, time to cannulation, and predictors of AVF failure with multivariate analysis.

RESULTS

A total of 139 new access procedures was performed in 131 patients (age, 53 +/- 16 years; male, 51%; white, 60%; diabetic, 49%; actively undergoing dialysis, 50%; prior permanent access, 26%). The noninvasive imaging showed that 83% of the patients were candidates for AVF, with a mean of 2.7 +/- 2.1 possible configurations. Invasive imaging was abnormal in 38% (forearm arterial disease > central vein stenosis > inflow stenosis) and impacted the operative plan in 19%. AVF were performed in 90% of the cases (brachiobasilic > brachiocephalic > radiocephalic > radiobasilic), with prosthetic AVF performed primarily because of inadequate veins. Among the patients who underwent AVF, the 30-day mortality rate was 1%, the complication rate was 20% (wound, 10%; hand ischemia, 8%), and 24% needed a remedial procedure. The AVF matured sufficiently for cannulation in 84% of those with sufficient follow-up and was suitable for cannulation by 3.4 +/- 1.8 months. On the basis of an intention to treat approach, an AVF sufficient for cannulation developed in 71% of the 139 cases referred for access. The multivariate analysis predicted that female gender (odds ratio, 9.7; 95% CI, 2.2 to 43.5) and the radiocephalic configuration (odds ratio, 4.6; 95% CI, 1.1 to 18.6) were both independent predictors of failure of the fistula to mature.

CONCLUSION

With the aggressive algorithm, the construction of native AVF is possible in the overwhelming majority of patients presenting for new hemodialysis access.

Durability of antegrade synthetic aortomesenteric bypass for chronic mesenteric ischemia

OBJECTIVE

The optimal treatment (endovascular/open repair, conduit, configuration) for chronic mesenteric ischemia (CMI) remains unresolved. This study was designed to review the outcome of patients with CMI treated with antegrade synthetic aortomesenteric bypass.

METHODS

The study was designed as a retrospective review in an academic tertiary care medical center. Patients with CMI who underwent antegrade synthetic aortomesenteric bypass were identified from a computerized vascular registry (from January 1987 to January 2001) with antegrade synthetic aortomesenteric bypass as intervention. Outcome measures were functional outcome (symptom relief, weight gain) and both graft patency (duplex ultrasound/angiography) and survival rates as determined with life-table analysis.

RESULTS

Forty-seven patients (female, 70%; age, 62 +/- 12 years) underwent aortomesenteric bypass (aortoceliac/aortosuperior mesenteric, n = 45; aortosuperior mesenteric, n = 2) for CMI (abdominal pain, 98%; weight loss, 83%). In-hospital mortality rate was 11% (four multiple organ dysfunction, one bowel infarction), mean length of stay was 32 +/- 30 days, three patients (6%) were discharged to a nursing home, and one (2%) was discharged home on parenteral nutrition (duration 4 months). At a mean follow-up period of 31 +/- 27 months, all patients had relief of abdominal pain and 86% had gained weight (at > or =1 year follow-up: mean ideal body weight 103 +/- 22%; versus before surgery: 87 +/- 17%; P <.001). Fourteen patients (34%) had diarrhea at discharge that persisted more than 6 months in 10. One patient had acute mesenteric ischemia develop from a failed graft (at 20 months), two patients had recurrent CMI develop from failing grafts (at 46 months and 49 months), and one asymptomatic patient was found to have a failing graft with duplex ultrasound scan (at 17 months); all grafts were revised. Primary, primary assisted, and secondary 5-year graft patency rates with life-table analysis were 69% (standard error [SE], 17%), 94% (SE, 7%), and 100%, respectively, and the 5-year survival rate was 74% (SE, 12%).

CONCLUSION

Antegrade synthetic aortomesenteric bypass for CMI is associated with good functional outcome and long-term graft patency.

Direct evidence for tumor necrosis factor-alpha signaling in arteriogenesis

BACKGROUND

Arteriogenesis serves as an efficient mechanism for flow restoration after arterial occlusion. This process is associated with inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), although their role in arteriogenesis remains unclear. We hypothesized that arteriogenesis is reduced in mice lacking functional TNF-alpha or p55 receptor. To test this hypothesis, we developed a novel microsphere-based murine model of hindlimb perfusion measurement.

METHODS AND RESULTS

Unilateral femoral arteries of nude (n=9), TNF-alpha(-/-) (n=9), TNF-alpha receptor p55(-/-) (n=8), and p75(-/-) (n=8) mice as well as their appropriate genetic background controls were occluded. The nude mice underwent laser Doppler hindlimb flux measurements preoperatively, postoperatively, and after 7 days. Seven days after ligation, all animals underwent tissue perfusion determinations using fluorescent microspheres. Laser Doppler findings confirmed acute decrease in flux with falsely normal values after 1 week. Microsphere results from control mice showed perfusion restoration to values approximately 50% of normal within 7 days. TNF-alpha(-/-) mice demonstrated a significant reduction (45.1%) in collateral artery perfusion compared with controls (TNF-alpha(-/-) 22.4+/-5.1% versus B6x129 49.7+/-9.3%; P<0.01). p55(-/-) mice exhibited an almost identical 45.8% reduction in collateral artery formation (p55(-/-) 28.3+/-4.3% versus C57BL/6J 61.8+/-9.1%; P<0.01), whereas p75(-/-) mice were equivalent to controls (p75(-/-) 54.5+/-5.5%; P=0.13).

CONCLUSIONS

Microsphere techniques in mice offer a tool for the molecular dissection of arteriogenesis mechanisms. These results suggest that TNF-alpha positively modulates arteriogenesis probably via signaling through its p55 receptor.

Functional outcome after thoracoabdominal aortic aneurysm repair

OBJECTIVE

Repair of thoracoabdominal aortic aneurysms (TAAAs) is performed for the improvement of long-term survival and the preservation of function. The determination of functional outcome and the identification of predictors of survival and functional recovery after TAAA repair are key to proper patient selection.

METHODS

This retrospective review of clinical data was performed in an academic medical center. The demographics, Crawford aneurysm type (I-18, II-33, III-22, IV-28), preoperative risk factors, operative characteristics, and postoperative complications and outcomes were recorded from the medical records for 101 consecutive patients who underwent TAAA repair (58 elective and 43 urgent/emergent). Functional status and living situation at hospital discharge and 12 months after discharge were determined from follow-up examination records or telephone contact with surviving patients. The patients then were categorized into "good" (survival, home, discharge to rehabilitation center, ambulatory) or "bad" (death, discharge to or residence in a long-term care facility, non-ambulatory) outcomes.

RESULTS

The postoperative mortality rate was 17.8% (10% in elective cases and 28% in urgent cases), and significant postoperative complications occurred in 77% of the cases (pulmonary complications in 41%, renal complications in 28%, and cord injury in 12%). The mean length of stay was 22.8 + 23.6 days, and at discharge, 80% of the patients were sent to home or rehabilitation and 20% were sent to long-term care facilities. At 1 year, 15 additional patients had died. All but two patients who had been initially discharged to rehabilitation had returned home, but only two patients who had been discharged to long-term care facilities had returned home and both were nonambulatory. Therefore, the survival rate at 1 year was 67%, and only 52.4% of the patients had a "good" outcome at 1 year (survival rate was 78% and rate of "good" outcome was 63% in patients who underwent elective TAAA repair). Independent predictors of postoperative death and "bad" outcome were age more than 75 years, preoperative heart disease, duration of visceral ischemia, use of left atrial femoral bypass graft, postoperative renal dysfunction, and number of organs failing after surgery.

CONCLUSION

Survival and good functional outcome after TAAA repair is significantly less common than expected and is primarily predicted with intraoperative factors and postoperative complications. Improved operative techniques and limitation of visceral ischemia reperfusion injury may improve outcome after TAAA repair.

Interleukin-10 fails to modulate low shear stress-induced neointimal hyperplasia

INTRODUCTION

Overexpression of the anti-inflammatory cytokine interleukin-10 (IL-10) blocks atherosclerotic events in vivo, and IL-10 has been recently hailed as an "immunologic scalpel" for atherosclerosis. Alternatively, mice lacking IL-10 receiving atherogenic diets have increased occlusive lesions. It remains unclear whether such IL-10 modulation broadly applies to other forms of occlusive arterial remodeling. We hypothesized that lack of IL-10 would exacerbate, and exogenous or overexpression of IL-10 would abrogate low shear stress-induced neointimal hyperplasia (NIH).

METHODS

Wild-type (WT) and IL-10-deficient (IL-10-/-) mice underwent unilateral common carotid artery (CCA) ligation. Low shear stress in the patent ligated artery results in remodeling and formation of neointima containing BrdU and SMC alpha-actin-positive cells. Additional groups of WT mice underwent CCA ligation and were treated daily with intraperitoneal saline or 1 microg of human IL-10. Chronic delivery gene therapy approaches were also utilized to define the role of IL-10 signaling. WT mice were treated adventitially with 1 x 10(10) adenovirus/green fluorescent protein (Ad/gfp) and an Ad/empty control to confirm the veracity of adventitial delivery. Then, Ad viral IL-10 (vIL-10), Ad/empty, and virus buffer alone were applied directly to the adventitia of the CAA immediately following ligation. In separate experiments, 1 x 10(10) Ad/empty or Ad/vIL-10 was injected intramuscularly. CCAs were perfusion fixed 28 days postligation, the time at which NIH is near maximum.

RESULTS

IL-10-/- mice developed identical NIH areas compared to WT controls. Mice receiving IL-10 demonstrated NIH equivalent to saline controls. Mice receiving intramuscular or adventitial Ad/IL-10 developed high serum levels of IL-10 yet formed NIH areas similar to those of controls. Serum IL-10 levels were significantly higher (P = 0.04) with adventitial delivery. Mice treated adventitially with Ad/gfp showed reliable transfection of cells within the adventitia of CAA. No antibody to human IL-10 was found in the sera of intraperitoneal IL-10-treated mice, which failed to attenuate NIH.

CONCLUSION

Under the conditions of this experiment, lack of IL-10 does not exacerbate low shear stress-induced NIH, nor does exogenous administration or overexpression of IL-10 attenuate it. Despite high serum levels of vIL-10 in mice treated with ad/vIL-10 adventitially, there appears to be no therapeutic effect despite the confirmed transfection of adventitial cells. Discrepancies between these findings and previous research may be related to IL-10 dosing, inflammation induced by the adenoviral vector, or disparities between the NIH models.

The outcome in the United States after thoracoabdominal aortic aneurysm repair, renal artery bypass, and mesenteric revascularization

OBJECTIVES

The purpose of this study was to determine outcome and identify predictors of death after thoracoabdominal aortic aneurysm (TAA) repair, renal artery bypass (RAB), and revascularization for chronic mesenteric ischemia (CMI).

PATIENTS AND METHODS

In this retrospective analysis, data were obtained from the Nationwide Inpatient Sample, a 20% all-payer stratified sample of hospitals in the United States during 1993 to 1997. Patients were identified by the presence of a diagnostic or procedure code from the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The main outcomes we examined were death, ICD-9-CM -based complications, length of stay, hospital charges, and disposition. A multivariate model was constructed to predict death.

RESULTS

A total of 2934 patients were identified (TAA, 540; RAB, 2058; CMI, 336) in the database. The mean age was comparable (TAA, 69 +/- 9 years; RAB, 66 +/- 12 years; CMI, 66 +/- 11 years), but the breakdown between the sexes varied by procedure (male: TAA, 53%; RAB, 55%; CMI, 24%). The mortality rate (TAA, 20.3%; RAB, 7.1%; CMI, 14.7%), complication rate (TAA, 62.2%; RAB, 37.4%; CMI, 44.6%), and the percentage of patients discharged to another institution (TAA, 21.2%; RAB, 9.3%; CMI, 12.0%) were clinically significant for all procedures. The mortality rate for RAB was greater when performed concomitant with an aortic reconstruction (4.4% vs 8.3%). All three procedures were resource intensive as reflected by the median length of stay (TAA, 14 days; RAB, 9 days; CMI, 14 days) and median hospital charges (TAA, $64,493; RAB, $36,830; CMI, $47,390). The multivariate model identified several variables for each procedure that had an impact on the predicted mortality rate (TAA, 14%-76%; RAB, < 1%-46%; CMI, < 2%-87%).

CONCLUSIONS

The operative mortality rates across the United States for patients undergoing TAA repair and RAB are greater than commonly reported in the literature and mandate reexamining the treatment strategies for these complex vascular problems.

External-beam radiation therapy for improved dialysis access patency: feasibility and early safety

Rectenwald, J. E., Pretus, H. A., Seeger, J. M., Huber, T. S., Mendenhall, N. P., Zlotecki, R. A., Palta, J. R., Li, Z. F., Hook, S. Y., Sarac, T. P., Welborn, M. B., Klingman, N. V., Abouhamze, Z. S. and Ozaki, C. K. External-Beam Radiation Therapy for Improved Dialysis Access Patency: Feasibility and Early Safety. Radiat. Res. 156, 53-60 (2001).Prosthetic dialysis access grafts fail secondary to neointimal hyperplasia at the venous anastomosis. We hypothesized that postoperative single-fraction external-beam radiation therapy to the venous anastomosis of hemodialysis grafts can be used safely in an effort to improve access patency. Dogs (n = 8) underwent placement of expanded polytetrafluoroethylene grafts from the right carotid artery to the left jugular vein. Five dogs received single-fraction external-beam photon irradiation (8 Gy) to the venous anastomosis after surgery. Controls were not irradiated. Shunt angiograms were completed 3 and 6 months postoperatively. Anastomoses, mid-graft, and the surrounding tissues were analyzed. Immunohistochemistry for smooth muscle cell alpha-actin, proliferating cellular nuclear antigen (PCNA), and apoptosis was performed. Incisions healed well, though all animals developed wound seromas. One control suffered graft thrombosis 4 months postoperatively. Angiography/histology confirmed severe neointimal hyperplasia at the venous anastomosis. The remaining seven dogs developed similar amounts of neointimal hyperplasia. PCNA studies showed no accelerated fibroproliferative response at irradiated anastomoses compared to controls. Skin incisions and soft tissues over irradiated anastomoses revealed no radiation-induced changes or increase in apoptosis. Thus we conclude that postoperative single-fraction external-beam irradiation of the venous anastomosis of a prosthetic arteriovenous graft that mimics the situation in humans is feasible and safe with regard to early wound healing.

Experience in the United States with intact abdominal aortic aneurysm repair

OBJECTIVES

The purpose of this study was to determine the current outcome in the United States and to identify predictors of mortality and "bad outcome" after open, intact abdominal aortic aneurysm (AAA) repair.

METHODS

In a retrospective analysis, data were obtained from the Nationwide Inpatient Sample during 1994-1996. The Nationwide Inpatient Sample is a 20% all-payer stratified sample of nonfederal United States hospitals. Patients older than 49 years were identified by the presence of primary diagnostic (441.4-intact AAA) and procedure (38.44-resection of abdominal aorta with replacement) codes of the International Classification of Diseases, Ninth Revision (ICD-9 ). In-hospital mortality rate, discharge disposition, bad outcome (death or discharge to an institution), complications (ICD-9 postoperative codes), length of stay, and charges were determined. The mortality rate and bad outcome were analyzed by the use of patient demographics (age, sex, race), patient comorbidities (ICD-9 diagnostic codes), calendar year, and hospital characteristics (size, location, teaching status) with univariate and multivariate analyses.

RESULTS

We identified 16,450 intact AAAs repairs during the study years. The mean patient age was 72 +/- 7 (+/- SD) years, and most patients were male (79.7%) and white (94.6%). Most repairs were performed at large (67.3%), urban (92.5%), and nonteaching (66.7%) institutions. The in-hospital mortality rate was 4.2%, the overall complication rate was 32.4%, and 91.2% of patients were discharged home, whereas the bad outcome rate was 12.6%. The median length of stay was 8 days (mean, 10.0 +/- 8.1), and median hospital charges were $28,052 (mean, $35,681 +/- $33,006) in 1996 dollars. Multivariate analysis showed that the mortality rate (P <.05) increased with age (70-79 years, 1.8 odds ratio [OR] [95% CI, 1.4-2.3], > 79 years, 3.8 OR [95% CI, 2.9-4.9]), sex (female, 1.6 OR [95% CI, 1.3-1.9]), cerebral vascular occlusive disease (1.8 OR [95% CI, 1.3-2.5]), preoperative renal insufficiency (9.5 OR [95% CI, 7.7-11.7]), and more than three comorbidities (11.2 OR [95% CI, 3.6-35.4]). Multivariate analysis also showed that bad outcome was associated with the same variables in addition to hospital size (small/medium), year of procedure (1996), chronic obstructive pulmonary disease, and two to three comorbidities.

CONCLUSIONS

Outcome after open repair of intact AAA across the United States is quite good. Older, sicker patients may benefit from nonoperative treatment or the potentially lower risk endovascular approaches.

Direct evidence for cytokine involvement in neointimal hyperplasia

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) and interleukin 1 (IL-1) are proximal inflammatory cytokines that stimulate expression of adhesion molecules and induce synthesis of other proinflammatory cytokines. In addition, TNF-alpha and IL-1 influence vascular smooth muscle cell migration and proliferation in vitro. In view of the inflammatory nature of neointimal hyperplasia (NIH), we tested the hypothesis that endogenous TNF-alpha and IL-1 modulate low shear stress-induced NIH.

METHODS AND RESULTS

Mice underwent unilateral common carotid artery (CCA) ligation. Low shear stress in the patent ligated CCA has previously been shown to result in remodeling and NIH. Reverse transcriptase-polymerase chain reaction for TNF-alpha and IL-1alpha mRNA demonstrated both TNF-alpha and IL-1alpha mRNA in ligated CCAs, whereas normal and sham-operated CCAs had none. Mice lacking functional TNF-alpha (TNF-/-) developed 14-fold less neointimal area than WT controls (P:<0.05). p80 IL-1 type I receptor knockout (IL-1RI-/-) mice tended to develop less (7-fold, P:>0.05) neointimal area than WT controls. Furthermore, no IL-1alpha mRNA expression was detected in CCAs from TNF-/- mice; however, TNF-alpha mRNA expression was found in the IL-1RI-/- mice. Mice that overexpress membrane-bound TNF-alpha but produce no soluble TNF-alpha display an accentuated fibroproliferative response to low shear stress (P:<0.05).

CONCLUSIONS

These results directly demonstrate that TNF-alpha and IL-1 modulate NIH induced by low shear stress. NIH can proceed by way of soluble TNF-alpha-independent mechanisms. Specific anti-TNF-alpha and anti-IL-1 therapies may lessen NIH.

Long-term outcome after treatment of aortic graft infection with staged extra-anatomic bypass grafting and aortic graft removal

OBJECTIVE

The purpose of this study was to determine long-term outcome in patients with infected prosthetic aortic grafts who were treated with extra-anatomic bypass grafting and aortic graft removal.

METHODS

Between January 1989 and July 1999, 36 patients were treated for aortic graft infection with extra-anatomic bypass grafting and aortic graft removal. Extra-anatomic bypass graft types were axillofemoral femoral (5), axillofemoral (26; bilateral in 20), axillopopliteal (3; bilateral in 1) and axillofemoral/axillopopliteal (2). The mean follow-up was 32.3 +/- 4. 8 months.

RESULTS

Four patients (11%) died in the postoperative period, and two patients died during follow-up as a direct consequence of extra-anatomic bypass grafting and aortic graft removal (one died 7 months after extra-anatomic bypass graft failure, one died 36 months after aortic stump disruption). One additional patient died 72 months after failure of a subsequent aortic reconstruction, so that the overall treatment-related mortality was 19%, whereas overall survival by means of life table analysis was 56% at 5 years. No amputations were required in the postoperative period, but four patients (11%) required amputation during follow-up. Twelve patients (35%) had extra-anatomic bypass graft failure during follow-up, and six patients underwent secondary aortic reconstruction (thoracobifemoral [2], iliofemoral [2], femorofemoral [2]). However, with the exclusion of patients undergoing axillopopliteal grafts (primary patency 0% at 7 months), only seven patients (25%) had extra-anatomic bypass graft failure, and only two patients required amputation (one after extra-anatomic bypass graft removal for infection, one after failure of a secondary aortic reconstruction). Furthermore, primary and secondary patency rates by means of life table analysis were 75% and 100% at 41 months for axillofemoral femoral grafts and 64% and 100% at 60 months for axillofemoral grafts. Only one patient required extra-anatomic bypass graft removal for recurrent infection, and only one late aortic stump disruption occurred.

CONCLUSIONS

Staged extra-anatomic bypass grafting (with axillofemoral bypass graft) and aortic graft removal for treatment of aortic graft infection are associated with acceptable early and long-term outcomes and should remain a primary approach in selected patients with this grave problem.

Financial impact of tertiary care in an academic medical center

OBJECTIVE

To analyze the financial impact of three complex vascular surgical procedures to both an academic hospital and a department of surgery and to examine the potential impact of decreased reimbursements.

SUMMARY BACKGROUND DATA

The cost of providing tertiary care has been implicated as one potential cause of the financial difficulties affecting academic medical centers.

METHODS

Patients undergoing revascularization for chronic mesenteric ischemia, elective thoracoabdominal aortic aneurysm repair, and treatment of infected aortic grafts at the University of Florida were compared with those undergoing elective infrarenal aortic reconstruction and carotid endarterectomy. Hospital costs and profit summaries were obtained from the Clinical Resource Management Office. Departmental costs and profit summary were estimated based on the procedural relative value units (RVUs), the average clinical cost per RVU ($33.12), surgeon charges, and the collection rate for the vascular surgery division (30.2%) obtained from the Faculty Group Practice. Surgeon work effort was analyzed using the procedural work RVUs and the estimated total care time. The analyses were performed for all payors and the subset of Medicare patients, and the potential impact of a 15% reduction in hospital and physician reimbursement was analyzed.

RESULTS

Net hospital income was positive for all but one of the tertiary care procedures, but net losses were sustained by the hospital for the mesenteric ischemia and infected aortic graft groups among the Medicare patients. In contrast, the estimated reimbursement to the department of surgery for all payors was insufficient to offset the clinical cost of providing the RVUs for all procedures, and the estimated losses were greater for the Medicare patients alone. The surgeon work effort was dramatically higher for the tertiary care procedures, whereas the reimbursement per work effort was lower. A 15% reduction in reimbursement would result in an estimated net loss to the hospital for each of the tertiary care procedures and would exacerbate the estimated losses to the department.

CONCLUSIONS

Caring for complex surgical problems is currently profitable to an academic hospital but is associated with marginal losses for a department of surgery. Economic forces resulting from further decreases in hospital and physician reimbursement may limit access to academic medical centers and surgeons for patients with complex surgical problems and may compromise the overall academic mission.