Michael R. Hall

Vein graft adaptation and fistula maturation in the arterial environment

Veins are exposed to the arterial environment during two common surgical procedures, creation of vein grafts and arteriovenous fistulae (AVF). In both cases, veins adapt to the arterial environment that is characterized by different hemodynamic conditions and increased oxygen tension compared with the venous environment. Successful venous adaptation to the arterial environment is critical for long-term success of the vein graft or AVF and, in both cases, is generally characterized by venous dilation and wall thickening. However, AVF are exposed to a high flow, high shear stress, low-pressure arterial environment and adapt mainly via outward dilation with less intimal thickening. Vein grafts are exposed to a moderate flow, moderate shear stress, high-pressure arterial environment and adapt mainly via increased wall thickening with less outward dilation. We review the data that describe these differences, as well as the underlying molecular mechanisms that mediate these processes. Despite extensive research, there are few differences in the molecular pathways that regulate cell proliferation and migration or matrix synthesis, secretion, or degradation currently identified between vein graft adaptation and AVF maturation that account for the different types of venous adaptation to arterial environments.

The mouse aortocaval fistula recapitulates human arteriovenous fistula maturation

Several models of arteriovenous fistula (AVF) have excellent patency and help in understanding the mechanisms of venous adaptation to the arterial environment. However, these models fail to exhibit either maturation failure or fail to develop stenoses, both of which are critical modes of AVF failure in human patients. We used high-resolution Doppler ultrasound to serially follow mice with AVFs created by direct 25-gauge needle puncture. By day 21, 75% of AVFs dilate, thicken, and increase flow, i.e., mature, and 25% fail due to immediate thrombosis or maturation failure. Mature AVF thicken due to increased amounts of smooth muscle cells. By day 42, 67% of mature AVFs remain patent, but 33% of AVFs fail due to perianastomotic thickening. These results show that the mouse aortocaval model has an easily detectable maturation phase in the first 21 days followed by a potential failure phase in the subsequent 21 days. This model is the first animal model of AVF to show a course that recapitulates aspects of human AVF maturation.

Disturbed shear stress reduces Klf2 expression in arterial-venous fistulae in vivo

Laminar shear stress (SS) induces an antiproliferative and anti‐inflammatory endothelial phenotype and increases Klf2 expression. We altered the diameter of an arteriovenous fistula (AVF) in the mouse model to determine whether increased fistula diameter produces disturbed SS in vivo and if acutely increased disturbed SS results in decreased Klf2 expression. The mouse aortocaval fistula model was performed with 22, 25, or 28 gauge needles to puncture the aorta and the inferior vena cava. Duplex ultrasound was used to examine the AVF and its arterial inflow and venous outflow, and SS was calculated. Arterial samples were examined with western blot, immunohistochemistry, and immunofluorescence analysis for proteins and qPCR for RNA. Mice with larger diameter fistulae had diminished survival but increased AVF patency. Increased SS magnitudes and range of frequencies were directly proportional to the needle diameter in the arterial limb proximal to the fistula but not in the venous limb distal to the fistula, with 22‐gauge needles producing the most disturbed SS in vivo. Klf2 mRNA and protein expression was diminished in the artery proximal to the fistula in proportion to increasing SS. Increased fistula diameter produces increased SS magnitude and frequency, consistent with disturbed SS in vivo. Disturbed SS is associated with decreased mRNA and protein expression of Klf2. Disturbed SS and reduced Klf2 expression near the fistula are potential therapeutic targets to improve AVF maturation.

Metabolic Syndrome Predicts Restenosis after Carotid Endarterectomy

BACKGROUND Carotid endarterectomy (CEA) is an effective surgical option for stroke prophylaxis for most patients. Restenosis after CEA can lead to additional interventions and adverse outcomes, but the factors that predict restenosis are poorly understood. This study examined which risk factors, such as metabolic syndrome (MetS), are associated with restenosis after CEA. STUDY DESIGN This retrospective study examined the records of all patients who underwent CEA at the Veterans Affairs Connecticut Healthcare System during a 4-year period. Metabolic syndrome was defined as the presence of 3 or more of the following: hypertension (blood pressure ≥130 mmHg/≥85 mmHg); serum triglycerides ≥150 mg/dL; high-density lipoprotein ≤40 mg/dL; BMI ≥25 kg/m(2); and fasting blood glucose ≥110 mg/dL. Major adverse events were defined as death, stroke, or MI. Restenosis was defined as >50% stenosis on follow-up imaging. RESULTS Seventy-eight patients underwent 79 CEAs during the study period. All patients were male and 76% were white. Mean patient age was 72.6 years. The mean duration of follow-up was 5.2 years. Sixty-seven percent of patients had MetS. Patients with MetS were comparable with those without MetS in demographics and preoperative comorbidities, except for increased hypertension and diabetes, as expected, and chronic renal insufficiency (p = 0.05). There was no significant difference in long-term survival or freedom from MAE between patients with and without MetS. Restenosis was significantly higher in patients with MetS (p = 0.02) and occurred 2 years after CEA in patients with MetS only, with a large increase in restenosis after 5 years (p = 0.018). MetS was an independent predictor of restenosis in multivariable analysis (p = 0.01). CONCLUSIONS Metabolic syndrome is an independent predictor for restenosis after CEA in a high-risk population. More frequent and/or long-term surveillance might be warranted in patients with MetS after CEA.

Metabolic syndrome is associated with type II endoleak after endovascular abdominal aortic aneurysm repair

OBJECTIVE Type II endoleak is usually a benign finding after endovascular abdominal aortic aneurysm repair (EVAR). In some patients, however, type II endoleak leads to aneurysm sac expansion and the need for further intervention. We examined which factors, in particular the components of metabolic syndrome (MetS), would lead to an increase risk of endoleak after EVAR. METHODS The medical records of all patients who underwent EVAR between 2002 and 2011 at the Veterans Affairs Connecticut Healthcare System were reviewed. MetS was defined as the presence of three or more of the following: hypertension (blood pressure ≥130 mm Hg/≥90 mm Hg), serum triglycerides ≥150 mg/dL, serum high-density lipoproteins ≤50 mg/dL for women and ≤40 mg/dL for men, body mass index ≥30 kg/m(2), and fasting blood glucose ≥110 mg/dL. Development of endoleak, including specific endoleak type, was determined by review of standard radiologic surveillance. RESULTS During a 9-year period, 79 male patients (mean age, 73.5 years), underwent EVAR for infrarenal abdominal aortic aneurysm (mean 6.2 cm maximal transverse diameter). MetS was present in 52 patients (66%). The distribution of MetS factors among all patients was hypertension in 86%, hypertriglyceridemia in 72%, decreased high-density lipoprotein in 68%, diabetes in 37%, and a body mass index of ≥30 kg/m(2) in 30%. No survival difference was found between the MetS and non-MetS groups (P = .66). There was no difference in perioperative myocardial infarction or visceral ischemia immediately postoperatively between the two groups. Patients with MetS had a significant increase in acute kidney injury (n = 7, P = .0128). Endoleaks of all types were detected in 26% (n = 20) of all patients; patients with MetS had more endoleaks than patients without MetS (35% vs 7.4%, P = .0039). Of the 19 type II endoleaks, 79% were present at the time of EVAR and only 21% developed during surveillance; 95% had MetS (P = .0007). CONCLUSIONS Type II endoleak after EVAR for abdominal aortic aneurysm is associated with MetS. Whether these patients are subject to more subsequent intervention due to sac expansion is unclear. MetS may be a factor to consider in the treatment of type II endoleak.

Systemic Inflammatory Disease and Its Association With Type II Endoleak and Late Interventions After Endovascular Aneurysm Repair

IMPORTANCE Abdominal aortic aneurysms are associated with chronic inflammation within the aortic wall, and previous studies have suggested that chronic inflammation may be a consequence of a dysregulated and persistent autoimmune response. Persistent aortic remodeling after aneurysm repair could place the patient at risk for endoleak or sac rupture. OBJECTIVE To determine whether patients with systemic inflammatory disease and large aneurysms have persistent aortic remodeling after endovascular aneurysm repair (EVAR). DESIGN, SETTING, AND PARTICIPANTS The records of all patients who underwent EVAR between July 2002 and June 2011 at the Veterans Affairs Connecticut Healthcare System were included in this retrospective review. Patients were considered to have a systemic inflammatory disease when confirmed by a referring specialist. Post-EVAR surveillance was performed by yearly imaging. INTERVENTION Endovascular aneurysm repair. MAIN OUTCOMES AND MEASURES Significant endoleak, defined as endoleak and sac diameter increase of 0.5 cm or greater. RESULTS A total of 51 of 79 patients (65%) had a systemic inflammatory disease. These patients had similar comorbid conditions compared with patients without inflammation but significantly greater numbers of major postoperative complications after EVAR (23.5% vs 3.6%; P = .02) and overall postoperative complications after EVAR (27.5% vs 7.1%; P = .03). Patients with a history of systemic inflammatory disease developed more endoleaks (45.1% vs 17.9%; P = .02) and late sac expansion (51.0% vs 21.4%; P = .01) and required more interventions (21.6% vs 3.6%; P = .03) during long-term follow-up. Systemic inflammatory disease was significantly associated with significant endoleak (odds ratio, 5.18; 95% CI, 1.56-17.16; P = .007). CONCLUSIONS AND RELEVANCE Patients with systemic inflammatory disease are at high risk for postoperative complications, type II endoleak, sac expansion, and additional interventions after EVAR. Additional strategies for improving the efficacy of EVAR in these patients may be warranted.

Chronic kidney disease predicts long-term mortality after major lower extremity amputation.

Background: Despite low peri-operative mortality after major lower extremity amputation, long-term mortality remains substantial. Metabolic syndrome is increasing in incidence and prevalence at an alarming rate in the USA. Aim: This study was to determine whether metabolic syndrome predicts outcome after major lower extremity amputation. Patients and Methods: A retrospective review of charts between July 2005 and June 2010. Results: Fifty-four patients underwent a total of 60 major lower extremity amputations. Sixty percent underwent below-knee amputation and 40% underwent above-knee amputation. The 30-day mortality was 7% with no difference in level (below-knee amputation, 8%; above-knee amputation, 4%; P = 0.53). The mean follow-up time was 39.7 months. The 5-year survival was 54% in the whole group, and was independent of level of amputation (P = 0.24) or urgency of the procedure (P = 0.51). Survival was significantly decreased by the presence of underlying chronic kidney disease (P = 0.04) but not by other comorbidities (history of myocardial infarction, P = 0.79; metabolic syndrome, P = 0.64; diabetes mellitus, P = 0.56). Conclusion: Metabolic syndrome is not associated with increased risk of adverse outcomes after lower extremity amputation. However, patients with chronic kidney disease constitute a sub-group of patients at higher risk of postoperative long-term mortality and may be a group to target for intervention.

CD44 Promotes Inflammation and Extracellular Matrix Production During Arteriovenous Fistula Maturation

Objective— Arteriovenous fistulae (AVF) remain the optimal conduit for hemodialysis access but continue to demonstrate poor patency and poor rates of maturation. We hypothesized that CD44, a widely expressed cellular adhesion molecule that serves as a major receptor for extracellular matrix components, promotes wall thickening and extracellular matrix deposition during AVF maturation. Approach and Results— AVF were created via needle puncture in wild-type C57BL/6J and CD44 knockout mice. CD44 mRNA and protein expression was increased in wild-type AVF. CD44 knockout mice showed no increase in AVF wall thickness (8.9 versus 26.8 &mgr;m; P=0.0114), collagen density, and hyaluronic acid density, but similar elastin density when compared with control AVF. CD44 knockout mice also showed no increase in vascular cell adhesion molecule-1 expression, intercellular adhesion molecule-1 expression, and monocyte chemoattractant protein-1 expression in the AVF compared with controls; there were also no increased M2 macrophage markers (transglutaminase-2: 81.5-fold, P=0.0015; interleukin-10: 7.6-fold, P=0.0450) in CD44 knockout mice. Delivery of monocyte chemoattractant protein-1 to CD44 knockout mice rescued the phenotype with thicker AVF walls (27.2 versus 14.7 &mgr;m; P=0.0306), increased collagen density (2.4-fold; P=0.0432), and increased number of M2 macrophages (2.1-fold; P=0.0335). Conclusions— CD44 promotes accumulation of M2 macrophages, extracellular matrix deposition, and wall thickening during AVF maturation. These data show the association of M2 macrophages with wall thickening during AVF maturation and suggest that enhancing CD44 activity may be a strategy to increase AVF maturation.

Assessing Interest and Barriers for Resident and Faculty Involvement in Global Surgery

BACKGROUND Multiple institutions have developed international electives and sustainable global surgery initiatives to facilitate clinical, research, and outreach opportunities with hospitals in resource-poor areas. Despite increasing interest among programs, many institutions have not successfully reached potential involvement. OBJECTIVE This study evaluates the experiences of Yale residents and faculty, measures interest in the development of an international surgical elective, and enumerates barriers to developing or participating in these opportunities. This was performed to develop a formalized elective and assess interest and capacity for surgical global health initiatives, as a seemingly increasing number of trainee applicants and residents were expressing interest in working in resource-poor settings. METHODS Electronic survey of Yale Surgery residents and faculty analyzed using SPSS and Graphpad Prism. RESULTS Among residents, previous global experience correlates with current interest in international opportunities, with 100% remaining interested, and 78% of those without prior experience also expressing interest (p = 0.018). Barriers to pursuing these activities included the use of vacation time, funding, scheduling, family obligations, and concern for personal safety. Among faculty, 28% of respondents have been involved internationally, and most (86%) expressed interest in additional opportunities and all were willing to take residents. Barriers to faculty participation included funding, relative value unit target reduction, protected time, and the desire for institutional support for such activities. CONCLUSIONS A substantial proportion of residents and faculty have experience in global health and motivation to pursue additional opportunities. The main barriers to participation are not a lack of interest, but rather needs for funding support, protected time, and institutional recognition of academic contributions. These findings are being used to develop a global surgery elective and establish long-term partnerships with international colleagues.

Getting Your IACUC Proposal Approved

Before the use of animals in any type of study can be done, the investigator must formulate and submit a proposal to the Institutional Animal Care and Use Committee (IACUC). A self-regulating entity, the IACUC is a part of any institution that uses laboratory animals for research or instructional purposes and oversees all aspects of an institution’s animal care and use. The IACUC protocol is an important element in establishing a research project for the principal investigator (PI) and his/her lab members as well as the institution under which the laboratory resides. In keeping with federal regulations, under the Laboratory Animal Welfare Act passed by Congress in 1966 (Public Law 89–544 Act of August 24, 1966. National Agriculture Library. United States Department of Agriculture. http://awic.nal.usda.gov/public-law-89-544-act-august-24-1966. Accessed 13 Jan 2013), this ensures the safety and humane handling of animals during your research. A properly reviewed and approved protocol will give your project merit and will help you focus on your project’s rationale and validity. Many IACUCs will have a specific application form to fill out. Here we provide a step-by-step introduction to writing, revising, and achieving approval of an IACUC protocol for research involving the use of laboratory animals. Where appropriate, examples from our own approved IACUC protocols are given.