**3. Arteriovenous fistulas**

In 1966, Brescia et. al. created a connection between an artery and a vein and allowed it to mature giving rise to the AVF [16]. This was groundbreaking in delivering optimal blood flow for hemodialysis. Initial side-to-side anastomoses had issues with hand edema, so it was further refined to end-to-end anastomoses to prevent this. Even today, AVFs have lower infection rates and better patency than CVCs, as they remain the ideal option for dialysis access.

In the last decade, endovascular techniques have been devised to create AVFs, revolutionizing dialysis access creation with the power to improve patient access to high-quality AVFs. Two novel devices for endovascular interventions have been approved by the US Food and Drug Administration.

The first device, the everlinQ endoAVF system (TVA Medical, Austin, TX), was studied in the Novel Endovascular Access Trial (**Figure 2**) [17, 18]. This uses radiofrequency energy and catheter technology to create an AVF. Specifically in this procedure, the brachial vein is penetrated with a needle and guidewire, which is then passed into the ulnar vein. Separately, the brachial artery is punctured in an antegrade direction, and a guidewire is advanced to the ulnar artery. A venous magnetic catheter is introduced into the ulnar vein, while an arterial magnetic catheter is introduced

#### **Figure 2.**

*EverlinQ EndoAVF system. This system allows for an endovascular approach to creation of an arteriovenous fistula (AVF). A venous magnetic catheter is introduced into the vein, while an arterial magnetic catheter is introduced into the artery. An anastomosis between the vein and artery is created as the magnetic catheters are aligned, allowing for activation of a radiofrequency electrode and creation of an AVF. Reprinted from: [17]. Copyright 2022, with permission from Elsevier. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/).*

into the ulnar artery. An anastomosis is created between the ulnar artery and vein as the magnetic catheters are aligned, allowing for activation of a radiofrequency electrode. In the trial examining 59 AVFs created using this technique, the primary and cumulative patency at 12 months were 69 and 84%, respectively. Mean time for fistula maturation was 111 days [18].

The second device used to create an AVF is the thermal resistance anastomosis device (TRAD) [19]. This uses thermal resistance energy to create an anastomosis between a vein and artery. In this procedure, a needle cannulates the vein (usually brachial or cubital) in a retrograde fashion using ultrasound, and then punctures into the proximal radial artery, allowing a guidewire to follow. Next, the TRAD advances into the vein-artery junction and creates a durable anastomosis. Angioplasty is done afterwards to augment flow into this anastomosis. In a study examining 107 percutaneous AVFs created using this Ellipsys Vascular Access System (Avenu Medical, San Juan Capistrano, CA), cumulative patency at 90, 180, and 360 days was 91.6, 89.3, and 86.7%, respectively [19].

These early results demonstrate that AVFs can be created through endovascular intervention, with reliable function afterwards. This can be accomplished by interventionalists without general anesthesia. If this were to become mainstream, patients needing dialysis access creation would have many more options rather than the necessity of waiting to see a vascular surgeon for AVF creation. Access to dialysis creation would be revolutionized.

Far infrared therapy has been studied for its effects in improving maturation and patency of newly created AVFs [20]. These are electromagnetic waves that may improve cutaneous blood flow. Many theorized mechanisms have been postulated

*Innovations in Hemodialysis Access DOI: http://dx.doi.org/10.5772/intechopen.110467*

for how it may improve AVF function, including thermal effects, inflammation suppression, and decreased oxidative injury. In a randomized controlled study of 122 patients, 62 patients received 40 minutes of far infrared therapy 3 times weekly for a year. The intervention group had a higher blood flow rate, a lower occurrence of AVF malfunction (12% vs. 29%, p = 0.02), and more cumulative unassisted patency (87% vs. 70%, p = 0.01) within 12 months [20].

Neointimal hyperplasia presents a challenge to the patency of vascular access. Because of this, it is a therapeutic target. Vonapanitase (recombinant human elastase) has been studied in a randomized controlled trial to determine if it improved primary and secondary patency [21]. It is known to disrupt elastin and other peptides that may attract cell proliferation, and has potential benefit in improving AVF patency. When applied during radiocephalic AVF creation, vonapanitase reduced primary (HR = 0.37, p = 0.02) and secondary (HR = 0.24, p = 0.046) patency loss. It also was associated with fewer procedures to restore or maintain fistula patency. However, there was no significant difference in risk of primary patency loss with vonapanitase overall in this study. Further research is essential to evaluate the efficacy of vonapanitase in improving dialysis access patency.
