While present day best practices for HD access vary from patient to patient, observational studies have shown that AVFs, compared to central venous catheters and arteriovenous grafts, have longer patency and access survival, and fewer complications including infection, stenosis and thrombosis. Despite the introduction of new fistula surgical techniques and locations over the last fifty-four years, AVFs are mired by high primary failure rates. In fact, USRDS data shows that of all AVFs placed between June 2014 and May 2016, 38.9% failed to mature sufficiently for use in dialysis (USRDS 2018, PDF link). It has also been shown that AVFs that require multiple interventions to assist with maturation have poor long term access patency (Harms et al. J Vasc Surg 2016). Additionally, the high the failure rate of dialysis arteriovenous access due to vascular stenosis remains pervasive, contributing to significant morbidity and mortality; including but not limited to missed or inadequate treatments, hospitalization, incident catheter use, infectious complications and death (USRDS 2010, PDF link).
Vascular stenosis occurs due to endothelial and smooth muscle injury resulting in neointimal hyperplasia. Percutaneous transluminal angioplasty (PTA) is the standard treatment for AV access stenosis, but unfortunately it causes vessel wall trauma further contributing to intimal hyperplasia and restenosis. In this scenario, the intervention itself contributes to the pathophysiologic process implicated in AVF stenosis. Not surprisingly, balloon angioplasty is associated with poor patency rates and high-reintervention rates. In a systematic review and meta-analysis, the primary AVF patency rates post-balloon angioplasty were 50% at 6 months, and 20% at 12 months (Wee et al. J Vasc Surg 2019).
More recent data shows that the annual vascular access costs in the United States are approximately $2.8 billion annually (Thamer et al, AJKD 2018). Vascular access related complications and resultant interventions cause significant morbidity and mortality. Therefore, undoubtedly there is a need for innovation in this arena to improve AVF outcomes.
In addition to standard balloon angioplasty, endovascular stents have shown promise in improving patency for some anatomic locations in AV accesses, such as the AVG venous anastomosis. (Haskal et al. NEJM 2010, Vesely et al. J Vasc Surg 2016). However, balloon angioplasty remains the standard of care and the first line treatment for most AV access stenosis.
The percutaneous endovascular AVF (endoAVF) techniques utilizing the WavelinQ and Ellipsys systems introduced over the last 5 years have demonstrated promising results, yielding lower AVF primary failure rates and lower reintervention rates. (NEAT & PIVOTAL trials; Hull et al. J Vasc Interv Radiol 2018, Lok et al. AJKD 2017, Yang et al. J vasc Access 2017). Unfortunately, not all patients fulfill the criteria required to qualify for endovascular AVF creation. Additionally, endovascular AVF outcomes have not been directly compared to surgical AVFs. Hence, endovascular AVFs provide additional vascular access options for patients but are not a replacement for surgical AVFs. See the 2020 NephMadness scouting report for more on this topic.
To combat neointimal hyperplasia and restenosis, the concept of a drug coated balloon (DCB) was introduced two decades ago with the first animal trial beginning in 2002. Paclitaxel crystals, derived from a cytotoxic agent that blocks the cell cycle during mitosis, are loaded onto the DCB and delivered directly to the vessel wall during balloon deployment. The crystalline formulation has a half-life of weeks to months, delivering prolonged vessel exposure to the drug, inhibiting the smooth muscle remodeling and fibrosis that contributes to stenosis. The first human trial of DCB began in 2003. DCBs have been used successfully in the treatment of coronary and peripheral artery disease for the revascularization of stenotic lesions (Scheller et al, NEJM 2006, Rosenfield et al. NEJM 2015).
The efficacy data for DCB use for stenotic lesions in dialysis vascular access has been mixed. Multiple single-center and small randomized control trials have demonstrated safe and effective use of DCB for AVF stenosis at 6 and 12 months post-intervention. See summary studies and outcomes of DCB use in dialysis vascular access below (Wee et al. J vasc Surg. 2019).