Drug Eluting Balloon for Early Fistula Failure Trial

Hemodialysis (HD) remains the most prevalent form of RRT for patients with End Stage Renal Disease (ESRD). Just in the United States there are more than 380,000 patients with ESRD on hemodialysis (HD) and the number is expected to increase to 500,000 by the year 2020. Recent data provided by Saudi Centre for Organ Transplantation (www.scot.org.sa) shows that there are just over 13000 patients with End-stage renal disease (ESRD) on hemodialysis in the Kingdom of Saudi Arabia. This number is expected to rise at a rate of 7-8% annually reaching 18000 by year 2018. Establishing a viable vascular access is crucial and is considered the 'life-line' for such patients. Loss and dysfunction of vascular access is a significant contributor to morbidity in ESRD patients on HD. In the United States <50% of all hemodialysis accesses remain patent at 3 years with the economic burden of maintaining vascular access patency calculated to exceed $1 billion with a >6% annual trend. The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines suggest that all ESRD patients should initiate dialysis with a functioning permanent vascular access with arteriovenous fistulas (AVF) preferred over arteriovenous grafts (AVG). Central venous catheters (CVC) are the least preferred vascular access for HD due to the complications associated with them. Despite these recommendations and clear benefits of using arteriovenous access for hemodialysis, up to 80% patients start dialysis with a CVC. One of the reasons for low AVF rates is early fistula failure (EFF). EFF is defined as an AVF that never develops adequately for dialysis (failure to mature) or which fails within 3 months of starting dialysis. An adequate AVF for dialysis according to KDOQI guidelines is the one which a) Has a flow of greater than 600ml/min, b) Has a diameter of 0.6cm or greater and c) Is approximately not deeper than 0.6cm from the skin surface. Between 23%-46% of newly constructed AVF have problems with early failure resulting in a dismal one year patency of 60-65%.

In order to devise a strategy to prevent EFF, one needs to understand the physiology of fistula maturation. Creation of an AVF leads to an immediate increase in flow through the vein due to the pressure gradient created. This increase in flow leads to increase wall shear stress which is defined mathematically by the formula 4ηQ/πr3, where η is blood viscosity, Q is blood flow and r is vessel radius. Shear stress thus is directly proportional to blood flow while inversely proportional to vessel diameter. After the creation of the AVF, the flow mediated increase in shear stress is mitigated by vessel dilatation through biological mediators. Consequently the shear stress is brought back to pre-anastomosis levels leading to vessel dilation. It seems that this positive remodeling of the vein leading to AVF maturation is dependent on increase in blood flow rather than the increase in pressure. Any pathology affecting the blood flow through the newly constructed AVF can thus lead to failure to mature.

The two most important causes for EFF amenable to intervention are stenosis anywhere in the circuit (present in around 80% of EFF) and/or presence of accessory veins. While stenosis development is pathological and accessory vein presence is natural, both lead to decreased blood flow through the main AVF circuit, which may be responsible for failure to mature. Addressing these two entities in a timely fashion can lead to salvage of many AVF, which otherwise would have been abandoned.

Development of neo-intimal hyperplasia (NIH) is the main pathology causing stenosis in the AVF circuit. There are many factors thought to be responsible for the development of this NIH. These include turbulent flow with wall shear stress disturbances, uremic endothelial dysfunction, repeated venipunctures, and unique anatomic factors. The pathogenesis includes migration of smooth muscle cells and myofibroblasts from media to intima, neoangiogenesis of microvessels inside neointima, and high levels of inflammatory blood markers.

Since its introduction, endovascular approach has shown a high rate of technical success in the treatment of stenotic lesions related to HD arteriovenous access. Percutaneous balloon angioplasty (PBA) is considered the treatment of choice for these lesions. Despite good technical and immediate success PBA has poor long term outcomes with recurrence rates of 60-70% at 6 months. One of the reasons could be the damage caused by angioplasty itself leading to intima-media rupture promoting the cascade of events leading to further development of NIH. Recently the use of covered stents at the time of angioplasty has shown better patency rates at 6 months but still not optimal. Lately the idea of delivering loco-regional pharmacological agents at the time of angioplasty to prevent NIH from happening has been extensively studied mostly in coronary arteries. This lead to the development of drug eluting stents and drug eluting balloons (DEB). These therapies have shown considerable advantage in clinical trials related to coronary and peripheral arterial disease. Although promising but advantages in coronary and peripheral arteries may not be applicable to arteriovenous access where the lesions are mostly venous with different characteristics. The role of these more costly interventions needs to be addressed in stenosis related to AVF, before wide spread use can be recommended. In a recent randomized non-blinded study involving 40 patients, Kostanos et al showed better 6 month patency rates (70% vs 25%) with DEB angioplasty as compared to standard PBA. The study is non-blinded and involved both AVG and AVF with target lesion spread all over the arteriovenous access circuit. Patane et al recently performed a study on 26 failing radiocephalic AVF's with juxta-anastamosis stenosis, defined as stenosis within 3 cm of arteriovenous anastamosis. In this study DEB angioplasty showed a 6 month primary patency of 96.1% which is much higher than historical conventional balloon angioplasty. The investigators targeted a lesion which resembles more closely arterial lesions where DEB has been shown to be effective, which seems more reasonable but there were no controls in the study. Due to the lack of a control group such high patency rates become questionable. Nevertheless this study highlights the importance of doing a randomized control trial targeting a specific lesion. In a controlled pilot study of radio-cephalic AVF with inflow stenosis Lai et al from Taiwan showed short term patency benefits with DEB angioplasty as compared to standard PBA. This being a pilot study had only 20 patients and was not adequately powered to answer the question. If these results are indeed proven to be true, this can lead to great improvement in patency of AVF's. In a randomized control trial the researchers are planning to assess the efficacy of DEB angioplasty as compared to standard PBA in AVF's with EFF.