Cath Lab Digest

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