Significance and Method of Balloon Angioplasty for Arteriovenous Fistula in Dialysis Patients with Residual Stenosis ≤30% as a Success Indicator

Introduction

Balloon angioplasty for arteriovenous fistulas (AVF) is a useful treatment for maintaining AVF, but its patency rate is not satisfactory.^1,2

A residual stenosis ≤30% is the success indicator for balloon angioplasty for AVF.³ In particular, paclitaxel-coated balloons are indicated when residual stenosis ≤30% or less on pre- and post-dilation angiography,⁴ underscoring the importance of achieving this target.

However, there are no optimal procedural strategies for reliably achieving ≤30% residual stenosis, and evidence on the association between achieving this goal and clinical outcomes is limited.

This study aims to evaluate methods for reducing residual stenosis to ≤30% and to investigate the associated 1-year patency outcomes.

Materials and Methods

This study is a single-center retrospective study. We extracted 366 patients who underwent balloon angioplasty for AVF in the forearm and anatomical snuff box at our hospital from January 2012 to August 2022.

Vascular access intervention (VAI) for arteriovenous graft was excluded. Cases with AVF in the elbow or upper arm were excluded. Tandem and completely occluded lesions were excluded. Thrombotic lesions requiring thrombus aspiration therapy were also excluded. Because the maximum balloon diameter in Japan must be ≤7 mm, lesions with target vessel diameters of ≥8 mm were excluded.

The remaining 198 cases were studied. The residual stenosis was measured by angiography after balloon dilatation. All cases were divided into two groups: (i) residual stenosis ≤30% (expanded group N=60) and (ii) group with residual stenosis ≥30% (non-expanded group N=138). The groups were compared in terms of procedural strategy and 1-year primary patency rate.

The reference vessel diameter was defined as the smaller diameter of the normal vessels on the central and peripheral sides of the lesion, measured by angiographic quantification. The residual stenosis was defined as “(minimum lesion diameter - target vessel diameter)/target vessel diameter × 100’’ measured by angiographic quantification after balloon dilation.

Primary patency was defined as the proportion of patients on dialysis for 1 year without the need for additional VAIs or shunt reconstruction. Regarding the indications for VAI to AVF, we perform dialysis shunt vascular echocardiography for cases with poor blood flow during dialysis, and the brachial artery blood flow must be ≤400 mL/min or the resistance index (RI) must be ≥0.60. It is indicated for cases with severe symptoms. Exceptionally, in cases where blood flow was ≤100 mL/min, we performed VAI without measuring brachial artery blood flow or RI, after vascular echocardiography revealed shunt vessel stenosis.

Interventional procedures were performed at the discretion of the operator, including selection of balloon size and balloon type. At our hospital, two cardiovascular interventional specialists perform VAI under angiography guidance. The balloon is selected by the operator as a compliant or scoring balloon. The scoring balloon used in our hospital is NSE PTA (NIPRO Japan) in all cases. In Japan, only one balloon can be used in one VAI. In all cases in this study, this was followed.

Written informed consent was obtained from all patients, and the study protocol was approved by our local institutional review board. The article conformed to the ethical guidelines of the 1975 Declaration of Helsinki. The article protocol was approved by the local Institutional Committee on Human Research at our institution.

Results

The rate of achieving a residual stenosis ≤30% after balloon dilatation was 30.3%. There were no significant differences in age, sex, height, weight, and BMI between the two groups [Table 1].

The two groups had no significant difference regarding the minimum lesion diameter on angiography before balloon dilatation (1.43±0.66 mm vs. 1.48±0.62 mm, P=0.60). There was also no difference in the stenosis rate before balloon dilation between the two groups (67.6% vs. 69.2%, P=0.74). The reference vessel diameter was significantly smaller in the expanded group than in the non-expanded group (4.41±0.93 mm vs. 4.81±1.08 mm, P=0.009).

Balloon size was significantly larger in the expanded group than in the non-expanded group (4.85±0.91 mm vs. 4.45±0.79 mm, P<0.001). The ratio of balloon size to control vessel diameter (balloon-to-vessel ratio) was significantly larger in the expanded group than in the non-expanded group (1.12±0.51 mm vs. 0.96±0.45 mm, P<0.001). The ROC curve an appropriate cutoff value of 0.96 for balloon-to-vessel ratio to achieve a residual stenosis rate ≤30% [Figure 1].

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Figure 1:

ROC curve for ratio of balloon size to reference vessel diameter and residual stenosis rate ≤30%. ROC: Receiver operating characteristic.

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In the expanded group, the scoring balloon usage rate (36.7% vs. 17.3%, P=0.003) was significantly higher [Table 2].

The scoring balloon group and conventional balloon group compared in terms of lesion location, stenosis rate, reference vessel diameter, age, and gender, with no significant differences between the two groups [Table 3]. The residual stenosis was significantly lower in the scoring balloon group than in the conventional balloon group (30.3% vs. 40.0%, P<0.001).

There was no significant difference between the two groups in the amounts of total fluoroscopy dose and contrast medium [Table 2]. No vessel perforation due to balloon dilation was observed. The one-year primary patency rate was significantly higher in the expanded group than in the non-expanded group (93.3% vs. 82.6%, P=0.04) [Figure 2].

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Figure 2:

Kaplan-Meier curve for primary patency.

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Discussion

Our study showed that only about 30% of cases achieved a residual stenosis <30% through balloon angioplasty. In Japan, only one balloon can be used per balloon angioplasty under health insurance. The inability to increase the balloon size is one of the reasons why many cases of balloon angioplasty are terminated without achieving a residual stenosis <30%. In fact, only one balloon was used in all cases in this study.

Our research suggests that the strategy for reducing the residual stenosis ≤30% in balloon angioplasty is to increase the ratio of balloon size to reference vessel as much as possible. Increasing the balloon size increases the risk of vascular perforation due to balloon expansion. It is necessary to know the appropriate balloon size to reduce the residual stenosis ≤30%. Our study suggests that a balloon-to-vessel ratio of 0.96 or higher is an appropriate strategy to achieve a residual stenosis ≤30%.

The use of a scoring balloon was also considered to be a useful strategy to achieve a residual stenosis ≤30% after balloon dilatation.

The scoring balloon used in this study (NSE PTA NIPRO Japan) is a specialized angioplasty balloon, designed to improve the efficacy of vessel dilation. It features three longitudinal nylon elements mounted on the balloon surface, which score the stenotic lesion during inflation. This focused force application allows for controlled plaque modification, enhanced luminal gain, and reduced elastic recoil while minimizing vessel trauma. It was believed that the characteristics of the scoring balloon led to a reduction in the residual stenosis.

Previous reports have also shown that vasodilation using a cutting balloon (type of scoring balloon with microsurgical blades on the surface of the balloon) improves the patency rate of AVF.^5,6 It has also been reported that treatment combining cutting and paclitaxel-coated balloons is safe.⁷ Cutting balloon can cut and disrupt the fibroelastic continuity of the ring of neointimal hyperplasia.⁸ This was thought to be the reason for reducing the residual stenosis rate. Although it is assumed that there is a risk of vascular perforation due to the use of scoring balloons, past reports have not shown an increase in vascular perforation when using scoring balloons in balloon angioplasty. In our current study, no vascular perforation was observed due to the scoring balloon.

We found no significant differences in patient background, pretreatment vessel diameter, or balloon size between the scoring and the conventional balloon groups. However, the residual stenosis after treatment was lower in the scoring balloon group. This reduction in residual stenosis may be one of the reasons why scoring balloons are more effective in balloon angioplasty.

The primary patency rate after balloon angioplasty in this study was higher than in previous reports.⁹ The exclusion of thrombotic lesions, occlusive lesions, tandem lesions, and graft vessels is thought to have led to high patency rate.

Our study is a single-center retrospective study. Operator bias exists because the strategy for balloon angioplasty, including selection of balloon and balloon size, is determined by the operator. We considered cases in which the brachial blood flow on ultrasound was ≤400 mL/min to be indications for VAI. This is because the Japanese health insurance system defines the indication for VAI as an upper arm blood flow ≤400 mL/min.

It is unclear whether similar results to ours would be obtained in countries or regions where indications for VAI are different. In Japan, due to the national insurance system, only one balloon is generally permitted per balloon angioplasty. If lesion dilation is inadequate, the use of additional balloons is not allowed. This limitation is thought to be a major reason why many cases in this study did not achieve a residual stenosis rate ≤30%. These results may differ from those in regions where there are no restrictions on the number of balloons that can be used.