In this retrospective analysis, the overall target lesion patency rates of CAS following PTA at 3, 6 and 12-months were 76.1%, 51.7% and 30.9%, respectively, which were comparable with the reported rates in literature (D’cruz et al., 2018). The target lesion patency rates following PTA with PCB at 3, 6 and 12-months were 68%, 52% and 22.7% respectively, with no significant differences compared to treatment with POBA. Mean estimated cephalic arch primary patency rates were also similar for the 2 groups.
While the superiority of PCB over POBA in preventing arteriovenous access re-stenosis has been demonstrated in several large scale randomized controlled trials in recent years, these studies have generally looked at arteriovenous accesses, and not specifically at the cephalic arch (Lookstein et al. 2020; Trerotola et al. 2018; Swinnen et al. 2018; Irani et al. 2018). The pathophysiology of development of stenosis differs across different anatomical sites in AVFs and may influence the treatment outcomes of PTA. This audit specifically compared PCB vs. POBA in the treatment of cephalic arch lesions and our findings failed to demonstrate a significant difference in terms of circuit primary and assisted patency rates and target lesion patency rates. This is likely due to the etiology of CAS being multifactorial in nature, with the anti-proliferative properties of PCB only addressing one of the many factors involved, and hence may not be superior to POBA alone. In addition, the structural properties of the cephalic arch will not be altered by the PCB, with the cephalic arch being compressed by surrounding rigid structures of the deltopectoral and claviculopectoral fascia causing haemodynamically significant stenosis which is susceptible to recoil post-PTA. Another reason contributing to the lack of difference between PCB vs. POBA for our audit could be due to a difference in Paclitaxel dosing of the PCB, with the majority of PCB used in our audit being of a dose of 2μg/mm2 compared to other studies with higher dosing of 3.5μg/mm2 (Lookstein et al. 2020; Swinnen et al. 2018; Irani et al. 2018).
Several studies have explored different technologies for prolonging the cephalic arch patency rates. In a small retrospective study including 17 patients with CAS, the use of cutting balloon angioplasty showed 3, 6, and 12-month patency rates of 94%, 81% and 38% respectively (Heerwagen et al. 2010). Although the patency rates appeared better than the reported rates in our audit and existing literature, the study did not directly compare cutting balloon angioplasty with POBA.
Bare metal stents serve as a metallic scaffold that preserve luminal gain following PTA and was thought to be able to prevent recoil and re-stenosis caused by extrinsic compression. However, results on the use of bare metal stents to treat CAS have been variable (D’cruz et al., 2018). Theoretically, in-stent re-stenosis can still occur due to cellular proliferation through the bare stent fenestration. Hence, deploying a stent without combating neointimal hyperplasia may not prolong the patency rates of the cephalic arch.
The stent graft, a type of covered vascular stent to impede neointimal hyperplasia and tissue in-growth, may therefore have the best potential to maintain the patency of the cephalic arch. Although only studied in small populations, the use of stent grafts have been encouraging with positive results reported. Rajan et al. reported target lesion patency at 3, 6 and 12-month of 100%, 100%, 29% respectively for stent graft vs. 60%, 0, 0 for PTA (Rajan and Falk 2015). Shemesh et al. compared bare metal stents to stent grafts for the treatment of CAS, and showed superior primary access patency rates of 39% vs. 82% at 3-months, and 0 vs. 32% at 12-months. It was however surprising to note that the 12-month CAS following stent graft deployment was similar to the reported rates of POBA in the current audit and several other studies (D’cruz et al., 2018; Shemesh et al. 2008). There have been increasing evidence showing that neointimal hyperplasia can occur at stent edges at a later stage, limiting flow and resulting in patency loss. As such, a combination of stent or stent graft with PCB may be the future direction for the treatment of CAS. In a prospective proof of concept study of 8 patients, a combination of helical stent and PCB have been shown to result in primary patency rates of 83.3% at 1-year (Tang et al. 2020). Although the stents used were bare metal stents, the positive results from this small study suggest that stent or stent graft placement in the cephalic arch with PCB treatment in-stent or along the stent edges may prevent neointimal hyperplasia and help to maintain long-term patency for CAS.
Besides endovascular techniques, acute restoration of AVF function and CAS treatment with surgical management has also been described. Davies et al. demonstrated superiority in patency rates of cephalic arch transposition or bypass compared to PTA or bare metal stent placement (Davies et al. 2017). However, the results were confounded by the fact that surgical interventions were offered only to younger and healthier patients. The risks of open surgey may outweigh its benefit in older patients with higher cardiac risk compared to endovascular treatment.
Our audit is limited by several factors: being a single centre audit, the findings may not be generalizable to other patient populations. Due to the inherent limitations of a retrospective audit, the results may have potential confounders. Furthermore, selection bias could not be excluded. Specifically, the group of patients who received PCB had a greater severity of CAS in terms of percentage of stenosis compared to POBA, which may have contributed to the failure to achieve patency improvement with PCB. However, recurrent and de novo stenosis, median time from prior intervention and previous stenting were similar (Table 2). In addition, due to the small sample size of the audit, a type 2 error cannot be excluded. Nonetheless, it is a unique study reporting PCB use solely in one location i.e. the cephalic arch and comparing to a POBA group performed over a similar period of time and by the same operators.