Marwan Tabbara

A Meta-analysis of Randomized Clinical Trials Assessing Hemodialysis Access Thrombosis Based on Access Flow Monitoring: Where Do We Stand?

The National Kidney Foundation Kidney Disease Outcomes Quality Initiative recommends the routine use of hemodialysis arteriovenous (AV) access surveillance to detect hemodynamically significant stenoses and appropriately correct them to reduce the incidence of thrombosis and to improve accesses patency rates. Access blood flow monitoring is considered as one of the preferred surveillance method for both AV fistulas (AVF) and AV grafts (AVG); however, published studies have reported conflicting results of its utility that led healthcare professionals to doubt the benefits of this surveillance method. We performed a meta‐analysis of the published randomized controlled trials (RCTs) of AV access surveillance using access blood flow monitoring. Our hypothesis was that access blood flow monitoring lowers the risk of AV access thrombosis and that the outcome differs between AVF and AVG. The estimated overall pooled risk ratio (RR) of thrombosis was 0.87 (95% confidence interval [CI], 0.67–1.13) favoring access blood flow monitoring. The pooled RR of thrombosis were 0.64 (95% CI, 0.41–1.01) and 1.06 (95% CI, 0.77–1.46) in the subgroups of only AVF and only AVG, respectively. Our results added to the uncertainty of access blood flow monitoring as a surveillance method of hemodialysis accesses.

Modified use of the Hemodialysis Reliable Outflow (HeRO) graft for salvage of threatened dialysis access.

The Hemodialysis Reliable Outflow (HeRO) graft (Hemosphere Inc, Eden Prairie, Minn) offers a new option to provide upper extremity arteriovenous (AV) dialysis access in patients with central venous occlusive disease. Creative use of this device can allow for salvage of failing or threatened AV fistulas and grafts. We present two patients who underwent a modified implantation of the HeRO device for immediate salvage of a malfunctioning AV access. Ipsilateral central venous occlusions were successfully overcome by anastomosing a HeRO device to the existing AV access and tunneled across the chest to the contralateral internal jugular vein.

Distinct impact of three different statins on arteriovenous fistula outcomes: a retrospective analysis.

Purpose Whether statins improve arteriovenous fistula (AVF) outcomes is still a matter of debate. Taking into consideration the existing physicochemical differences between individual drugs, this study evaluates the impact of three different statins (atorvastatin, rosuvastatin and simvastatin) on one-stage and two-stage AVF outcomes. Methods Using a retrospective cohort of 535 patients, we analyzed the effects of each statin on primary failure and primary patency using multivariate logistic regressions and Cox proportional hazard models. Results Out of the three statins analyzed, only atorvastatin improved the overall primary failure of AVF (odds ratio [OR] = 0.18, p = 0.005). Comparisons between the two AVF types demonstrated that this effect was due to a prominent reduction in primary failure of one-stage (OR = 0.03; p = 0.005), but not two-stage fistulas (OR = 0.43; p = 0.25). In contrast, primary patency of two-stage (hazards ratio [HR] = 0.51; p = 0.024), but not one-stage fistulas (HR = 0.98; p = 0.95), was improved by all statins as a group, but not by individual drugs. Conclusions Our results suggest that the potential benefit of statins on AVF outcomes is a drug-specific and not a class effect, and that such effect is also influenced by the type of fistula.

Fibrotic Venous Remodeling and Nonmaturation of Arteriovenous Fistulas

The frequency of primary failure in arteriovenous fistulas (AVFs) remains unacceptably high. This lack of improvement is due in part to a poor understanding of the pathobiology underlying AVF nonmaturation. This observational study quantified the progression of three vascular features, medial fibrosis, intimal hyperplasia (IH), and collagen fiber organization, during early AVF remodeling and evaluated the associations thereof with AVF nonmaturation. We obtained venous samples from patients undergoing two-stage upper-arm AVF surgeries at a single center, including intraoperative veins at the first-stage access creation surgery and AVFs at the second-stage transposition procedure. Paired venous samples from both stages were used to evaluate change in these vascular features after anastomosis. Anatomic nonmaturation (AVF diameter never ≥6 mm) occurred in 39 of 161 (24%) patients. Neither preexisting fibrosis nor IH predicted AVF outcomes. Postoperative medial fibrosis associated with nonmaturation (odds ratio [OR], 1.55; 95% confidence interval [95% CI], 1.05 to 2.30; P=0.03, per 10% absolute increase in fibrosis), whereas postoperative IH only associated with failure in those individuals with medial fibrosis over the populations median value (OR, 2.63; 95% CI, 1.07 to 6.46; P=0.04, per increase of 1 in the intima/media ratio). Analysis of postoperative medial collagen organization revealed that circumferential alignment of fibers around the lumen associated with AVF nonmaturation (OR, 1.38; 95% CI, 1.03 to 1.84; P=0.03, per 10° increase in angle). This study demonstrates that excessive fibrotic remodeling of the vein after AVF creation is an important risk factor for nonmaturation and that high medial fibrosis determines the stenotic potential of IH.

CD4(+) lymphocytes improve venous blood flow in experimental arteriovenous fistulae.

BACKGROUND The role of immune cells in arteriovenous fistulae (AVF) maturation is poorly understood and has received, until quite recently, little attention. This study examines the function of T lymphocytes in AVF vascular remodeling. METHODS Experimental fistulae were created in athymic rnu nude rats lacking mature T lymphocytes and euthymic control animals by anastomosing the left superior epigastric vein to the nearby femoral artery. Blood flow rates, wall morphology, and histologic changes were assessed in AVF 21 days after creation. The effect of CD4(+) lymphocytes on AVF maturation in athymic animals was analyzed by adoptive transfer of cells after fistula creation. RESULTS The absence of T lymphocytes compromised blood flow in experimental fistulae. Histopathologic inspection of AVF from athymic rats revealed that T-cell immunodeficiency negatively affected venous vascular remodeling, as evidenced by a reduced lumen, a thick muscular layer, and a low number of inflammatory cells compared with control animals. Adoptive transfer of CD4(+) lymphocytes from euthymic rats into athymic animals after fistula creation improved blood flow and reduced intima-media thickness. CONCLUSION These results point at the protective role of CD4(+) lymphocytes in the remodeling of the AVF vascular wall.

The Impact of Arteriovenous Fistulae on the Myocardium: The Impact of Creation and Ligation in the Transplant Era

Cardiac hypertrophy is a relatively common complication seen in patients with advanced chronic kidney disease (CKD) and end‐stage renal disease (ESRD). Moreover, cardiac hypertrophy is even more frequently seen in patients with ESRD who have an arteriovenous (AV) access. There has been substantial evidence pertaining to the effects of AV access creation on the heart structure and function. Similarly, there is increasing evidence on the effects of AV access closure, flow reduction, transplantation, and immunosuppressive medication on both endpoints. In this review, we present the evidence available in the literature on these topics and open the dialog for further research in this interesting field.

Similar degree of intimal hyperplasia in surgically detected stenotic and nonstenotic arteriovenous fistula segments: a preliminary report

Background. Intimal hyperplasia has been historically associated with improper venous remodeling and stenosis after creation of an arteriovenous fistula. Recently, however, we showed that intimal hyperplasia by itself does not explain the failure of maturation of 2‐stage arteriovenous fistulas. We seek to evaluate whether intimal hyperplasia plays a role in the development of focal stenosis of an arteriovenous fistula. Methods. This study compares intimal hyperplasia lesions in stenotic and nearby nonstenotic segments collected from the same arteriovenous fistula. Focal areas of stenosis were detected in the operating room in patients (n = 14) undergoing the second‐stage vein transposition procedure. The entire vein was inspected, and areas of stenosis were visually located with the aid of manual palpation and hemodynamic changes in the vein peripheral and central to the narrowing. Stenotic and nonstenotic segments were documented by photography before tissue collection (14 tissue pairs). Intimal area and thickness, intima‐media thickness, and intima to media area ratio were measured in hematoxylin and eosin stained cross‐sections followed by pairwise statistical comparisons. Results. The intimal area in stenotic and nonstenotic segments ranged from 1.25 to 11.61 mm2 and 1.29 to 5.81 mm2, respectively. There was no significant difference between these 2 groups (P = .26). Maximal intimal thickness (P = .22), maximal intima‐media thickness (P = .13), and intima to media area ratio (P = .73) were also similar between both types of segments. Conclusion. This preliminary study indicates that postoperative intimal hyperplasia by itself is not associated with the development of focal venous stenosis in 2‐stage fistulas.

Arteriovenous fistula maturation in patients with permanent access created prior to or after hemodialysis initiation

Introduction Multiple factors and comorbidities have been implicated in the ability of arteriovenous fistulas (AVF) to mature, including vessel anatomy, advanced age, and the presence of coronary artery disease or peripheral vascular disease. However, little is known about the role of uremia on AVF primary failure. In this study, we attempt to evaluate the effect of uremia on AVF maturation by comparing AVF outcomes between pre-dialysis chronic kidney disease (CKD) stage five patients and those who had their AVF created after hemodialysis (HD) initiation. Methods We included 612 patients who underwent AVF creation between 2003 and 2015 at the University of Miami Hospital and Jackson Memorial Hospital. Effects of uremia on primary failure were evaluated using univariate statistical comparisons and multivariate logistic regression analyses. Results Primary failure occurred in 28.1% and 26.3% of patients with an AVF created prior to or after HD initiation, respectively (p = 0.73). The time of HD initiation was not associated with AVF maturation in multivariate logistic regression analysis (p = 0.57). In addition, pre-operative blood urea nitrogen (p = 0.78), estimated glomerular filtration rate (p = 0.66), and serum creatinine levels (p = 0.14) were not associated with AVF primary failure in pre-dialysis patients. Conclusions Our results show that clearance of uremia with regular HD treatments prior to AVF creation does not improve the frequency of vascular access maturation.

Minimally invasive axillary to right atrial graft for hemodialysis access utilizing the intraluminal flow guard graft

As the medical treatment of patients suffering from endstage renal disease improves, patients are being maintained with chronic hemodialysis for longer periods of time. Lack of autologous venous conduits, complex central venous occlusive disease, and indwelling catheter or arteriovenous (AV) graft infections all pose a significant risk of morbidity and mortality (1). Several advancements have been developed to address these increasingly common problems, including immediate/ early access grafts, the Hemodialysis Reliable Outflow (HeRO) graft (Cryolife, Kennesaw, Georgia, USA) (2), the Gore Hybrid Vascular Graft (Gore Medical, Inc, Flagstaff, Arizona, USA), and the Flixene IFG (intraluminal flow guard) Graft (Atrium Medical, Hudson, New Hampshire, USA). The Flixene IFG graft combines an early access PTFE graft with a perpendicular ‘T-shaped’ stented venous outflow segment intended for inline placement in the outflow vein. The intended goal of this configuration is to redirect the turbulent flow and prevent venous intimal hyperplasia (3). We present the case of a 51-year-old male suffering from end-stage renal disease for 6 years, who had exhausted all traditional access sites. A Flixene IFG graft was successfully implanted in a minimally invasive fashion from the left axillary artery to the right atrium, providing a chest wall AV graft for hemodialysis. The patient had a history of severe learning impairment, requiring care in an adult assisted living facility. He had undergone countless AV access procedures (seen as multiple prior access scars in Fig. 1A, B arrows) over the last 6 years. On presentation, he was dialyzed via a transhepatic tunneled catheter, due to complete occlusions of all other upper and lower extremity central veins. This access had had to be re-