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Objective. To assess the effectiveness of cutting balloon angioplasty in the treatment of stenosis in hemodialysis arteriovenous fistulas (AVF). Materials and Methods. Over the past two years, we have observed 75 patients with hemodialysis AVFs. Twenty-one patients (mean age 66.4 years, range 51–81) with AVF stenosis (19 Cimino-Brescia fistulas and 2 loop grafts) were selected for cutting balloon angioplasty. In 10 cases, the cutting balloon device was used after failure of dilatation with a high-pressure balloon, while in 11 cases (9 focal stenosis and 2 restenosis), it was used as a primary approach. We utilized cutting balloons with the following diameters: 8 mm (n = 2), 6 mm (n = 10), 5 mm (n = 8) and 4 mm (n = 1). The follow-up was performed by color Doppler ultrasound (CDU) and clinical evaluation at 1, 3, 6, 12, 18 and 24 months. Results. In all patients, the post-procedure angiography demonstrated an immediate technical success. No peri-procedural complications occurred. In all cases, follow-up examinations (range 3–24 months, mean 11.1 months) demonstrated the patency of AVFs with CDU. All patients showed good function of the AVF during their dialysis. No further procedures were necessary. In one case, restenosis was observed, but it was not hemodynamically significant and did not result in flow reduction during dialysis. Conclusion. Cutting balloon angioplasty is safe and can be utilized as an alternative treatment for stenosis in hemodialysis AVFs, especially in cases of severe stenosis, with a low restenosis rate both in the short and medium term. However, further studies are necessary to assess the effectiveness of the device in improving the long-term AVF patency.

Introduction
Hemodialysis fistulas (AVFs) are an element of fundamental importance in the treatment of patients undergoing dialysis. Their correct functioning is an indispensable condition for the success of the dialysis procedure.

Interventional radiology has taken on an increasingly important role in the percutaneous management of failing grafts and fistulas.^1,2 In some patients, the fistula stenosis can be resistant to dilation with conventional angioplasty balloons^3,4 and even high-pressure balloons.⁵

The cutting balloon (Boston Scientific, Maple Grove, MN), utilized for the first time by Barath in 1991, is a device that combines the principles of conventional angioplasty with the techniques of microsurgery.⁶ Over the last decade, numerous series regarding this device have been published, most concerning the use of the device in the fields of cardiology⁷ and endo-urology.⁸ The cutting balloon has also been considered for other applications in the extra-cardiac vessel^9–16 and, in particular, for the treatment of stenosis in hemodialyisis AVFs.^3,17–19

Material and Methods
Of the 21 patients with tight focal stenosis of hemodialysis AVFs that were selected for cutting balloon angioplasty, 20 of 21 patients had radio-cephalic fistulas and 1 patient had a femoral fistula.
All patients presented a with “failing fistula” with a flow capacity < 300ml/min. Prior to the treatment, all patients were assessed with CDU (Philips ATL® 5000) to study the feeding artery, arterial anastomosis, graft, venous anastomosis and venous outflow to the subclavian artery. Stenosis greater than 50% was considered present if the maximum systolic velocity was more than 4 m/sec, the maximum velocity ratio was more than 3:1, or both. The velocity ratio was calculated by comparing the velocity of the area of suspected stenosis with the velocity next to the area of suspected stenosis.

On the basis of the abnormal findings of a preliminary angiography, a decision was made to carry out angioplasty of the venous stenosis. Informed consent was obtained from all patients. Focal tight stenoses due to intimal hyperplasia were considered suitable for treatment with a cutting balloon, either as a first treatment or after failure of high-pressure balloon angioplasty.

After opacifying the ipsilateral brachial artery (n = 20) and common femoral artery (n = 1) with Terumo® 4F glide catheters and crossing the anastomosis with a 0.035” Terumo hydrophilic guidewire, a 6-7Fr sheath was inserted and angioplasty with a high-pressure balloon (Blue Max®20™ Balloon Catheter, Boston Scientific) was performed.

Ten patients who underwent incomplete dilation with a high-pressure balloon were treated with a cutting balloon (Boston Scientific). The guidewire was exchanged for a 0.014” Terumo guidewire with a 5F catheter for advancing the cutting balloon. The dilatation was carried out with a syringe equipped with a manometer (Medflator II, Medex Medical, Carlsbad, CA) with a gradual inflation of the balloon until it reached a pressure of 20 atm if a high-pressure balloon was utilized, and 6 atm with the use of a cutting balloon. During the procedure, 2000 UI of heparin was administered. Cutting balloons with the following diameters were used: 8 mm (n = 2), 6 mm (n = 10), 5 mm (n = 8) and 4 mm (n = 1). Results were assessed by means of an angiographic study at the end of the procedure.

A follow-up was carried out using CDU after 1, 3, 6, 12, 18 and 24 months and by clinical assessment of the flow capacity of the fistula during the dialysis procedure.

Results
Of the 21 patients, preliminary angiography demonstrated the presence of stenosis at the level of the efferent vein in 17 patients (Figures 1a, 2a) and at the level of the anastomoses in the remaining 4 patients (Figures 1a, 3a). After incomplete dilation with a high-pressure balloon (Figures 3b-c), 10 patients were treated with a cutting balloon. In the other cases (9 focal stenosis and 2 cases of restenosis, respectively, at 6 and 9 months from a prior angioplasty), a “primary cutting balloon angioplasty” was carried out (Figures 1b, 2b). In 13 cases, complete resolution of the stenosis was achieved (Figures 1c, 3d). In 7 cases, the angiography carried out at the end of the procedure demonstrated a residual stenosis of < 10%, and in one case, a residual stenosis of 30% was detected. In this latter case, the elimination of collateral circles confirmed the hemodynamic success of the procedure (Figures 3c).

The device was inserted easily in 20 patients, resulting from the use of a 0.014” stiff guidewire. In the remaining case, the balloon advanced with difficulty due to the rigidity of the device and to the small caliber of the supporting guidewire. Eventually the sheath was advanced beyond the stenosis with the help of a stiff guidewire (Amplatz Super Stiff®, Boston Scientific) and the balloon was pushed inside the sheath, which was then removed before inflation.

cious thrombosis. In 3 cases, the cutting balloon ruptured when inflated at a pressure of 7 and 8 atm, but in all 3 cases, it was removed in one piece without any difficulty or complications. During the dilatation with the cutting balloon, none of the patients reported any pain.

Discussion
Constant monitoring of the fistula flow and the prompt treatment of a hemodynamically significant stenosis (> 50%) is necessary in order to increase the life of the fistula and to reduce the percentage of thrombosis.²⁰

Endovascular treatment has taken on a fundamental role in the follow-up of AVF accesses and today it represents the most appropriate therapeutic approach,²⁰ as it has a lower risk of complications compared to surgical treatment.⁵

Angioplasty is the most important endovascular treatment^1,2 for stenosis of the AVF, with a technical success rate of between 85 and 94%.²¹ Limitations of angioplasty, however, are in regard to resistant stenosis, especially in proximity to the anastomoses³ and may increase the rate of restenosis with a patency rate of 20–30% at 2 years.²¹

The elevated occurrence of recoil, determined by the particular pathogenic character of this type of stenosis,^3,4 has encouraged new device and alternative endovascular procedure research.¹⁸ As far as angioplasty is concerned, the use of high-pressure balloons^5,17 and prolonged inflation with devices, which allow the contemporaneous perfusion of the fistula³ have all been proposed. The integration with stenting does not seem to improve the results of angioplasty; furthermore, the presence of the stent increases the occurrence of thrombosis and reduces the area available for injections.²²

The cutting balloon combines the principles of microsurgery with percutaneous angioplasty, and its use was first proposed for coronary angioplasty in order to control intimal hyperplasia and to reduce the rate of restenosis.⁶ It is a non-compliant balloon equipped with 3 or 4 micro-blades mounted longitudinally along the external surface of the balloon (Figure 4). When the balloon is inflated, the micro-blades are exposed and are able to make controlled incisions in the intima so as to permit the dilatation of the vessel without the irregular lacerations caused by conventional balloons. These regular incisions mean a minimal exposition of the media with a reduction of the procoagulating activity, decreased local inflammation, and minor healing processes.^6,23 It appears that after dilatation with a cutting balloon there is a minor expression of vascular adhesion molecules for the platelets. In addition, the expression of growth factor and cell proliferation are not circumferential but limited to the incisions in the intima. These factors lead to a reduction in the rate of restenosis.²³

The action of the micro-blades creates an area of minor resistance in the fibrous band around the stenosis to permit the balloon to open. The cutting balloon can also increase the effectiveness of the conventional angioplasty by allowing a greater expansion of the balloon.3 Recent studies have produced positive results in resistant stenosis in other areas, especially where the reduced caliber is sustained by intimal and fibrous hyperplasia.^8–16

The use of this device in the venous area and particularly for the treatment of stenosis in AVF has been described by Vorverk in 1995.¹⁹ Literature reported the treatment of 24 cases with 91.6% immediate technical success, and with a restenosis rate of 16.6% during follow-up, carried out after an average period of 6.7 months (Table I).^3,17–19 Among the complications, only two cases of leakage from the venous walls were reported, but they resolved spontaneously without compromising the functioning of the fistula.³

In our study, we achieved an immediate technical and clinical success in 100% of patients and an absence of hemodynamically significant restenosis during follow-up after an average period of 11.1 months. No complications were observed during the procedure and the patients did not suffer any pain caused by the inflation of the balloon, contrary to that observed during angioplasty procedures using a high-pressure balloon. This observation is probably related to the fact that the incisions in the intima reduce the barotraumas on the vessel walls, as they require less inflation pressure. Neither did we observe any particular difficulty in advancing the balloon. We chose to use a rigid 0.014” guidewire, as the small caliber of the device and the supporting guide reduces the pushability.

On the base of data that emerged from personal experience and from the data reported in literature, we affirmed that angioplasty with a cutting balloon is safe and can be considered as an alternative treatment for stenosis of hemodialysis AVFs. It permitted us to achieve excellent results in cases of tight focal stenosis, resistant to dilatation with high-pressure balloons, with a low restenosis rate both in the short- and medium-term. Furthermore, the reduction of pain during the procedure increased patient compliance and comfort. However, further studies, with a greater number of patients and with a longer period of follow-up, are necessary in order to assess the effectiveness of the device to improve the long-term patency of the hemodialysis AVFs.

gcarraf@tin.it