Fig. 27.1
A proposed algorithm for evaluating a fistula postoperatively
Most often the etiology as to why the fistula is not maturing can be categorized into three basic categories. There may be problems with arterial inflow, the anastomosis, venous outflow, or a combination of the three. Through physical exam, ultrasound, and fistulagram, the etiology can most likely be delineated [15, 16].
Inflow issues may be due to a diseased artery. On physical exam, feel the artery and note if the artery feels soft and pliable as compared to calcified and hard. Take note if the artery feels small. The same things are evaluated on ultrasound, noting the size of the artery and any calcification. Look for areas of stenosis whether they are over a short segment or extended segment. Then compare the physical exam and ultrasound with the fistulagram. Imaging the arterial inflow in addition to the AVF may help differentiate possible etiologies.
Next, evaluate the anastomotic site. This can be difficult in the early postoperative period due to the swelling and wound healing. Tissues do not always lend themselves to a good physical exam or ultrasound. Obviously, if there is an excellent thrill and bruit, it is a nonissue. If there is a weak thrill and bruit, suspect an anastomotic stricture. When the patient comes for the next visit, there is a great likelihood that the anastomotic site can be evaluated more thoroughly with physical exam and ultrasound.
The outflow vein is then evaluated. On physical exam, examine if the fistula has a good thrill and bruit. If the vein is pulsatile and there is decreased flow during diastole on auscultation, then suspect an outflow stenosis or occlusion. Consider assessing whether you yourself are able to cannulate the AVF. The vein needs to be large, superficial, not tortuous, and have enough length where two needles can be placed. If access needles cannot be placed, then the AVF is inadequate or immature. Ultrasound is again used to evaluate this portion of the AVF and may show an area of stenosis or occlusion. A fistulagram is obtained to confirm findings. Venous problems include failure to dilate, intimal hyperplasia at the juxta-anastomotic area or at valves, branching of the vein, torturous veins, multiple collaterals, and stenotic and occluded segments. A vein that is too deep is not necessarily a failure of maturity, but rather merely an inadequate AVF. Many times this has been anticipated and there is a plan for correction.
Table 27.1 was created by reviewing a number of studies and tabulating the frequency as to the etiology why an AVF was felt not to be maturing [2, 3, 15, 17, 18].
Table 27.1
Frequency of the etiology as to why fistulas do not mature
AVF | Artery | Anastomosis | Swing point | Outflow vein | Central vein | Accessory vein | Multiple |
|---|---|---|---|---|---|---|---|
453 | 21 | 106 | 214 | 203 | 69 | 88 | 202 |
4.6 % | 23.4 % | 47.2 % | 49.8 % | 15.2 % | 19.4 % | 44.6 % |
Treatment
Arterial Inflow Problems
Treatment
- A.
Angioplasty
- B.
Bypass
Arterial inflow problems are not very common. It has been reported to be seen between 4 and 11 % of the time in immature AV fistulas [2, 3, 15, 17, 18]. When the problem is a focal stenosis, it can easily be treated with angioplasty with expected good outcomes.
Turmel–Rodrigues et al. presented good results in treating patients with radial artery stenosis. Some of their patients even had stenosis greater than 5 cm long. They used balloon angioplasty as their means of treatment. Primary patency at 1 and 2 years was 64 % and 61 %, respectively, with a secondary patency of 96 % and 94 % at 1 and 2 years, respectively [19].
When the artery is diffusely diseased over a long segment, bypass procedures can be considered. An example is an AVF that has been created at the wrist, and the radial artery is not deemed suitable to provide adequate flow into an otherwise good outflow vein. A bypass using polytetrafluoroethylene (PTFE) from the brachial artery to the vein can be performed. This maintains the use of a good vein that can still be used for cannulation. Obviously, this requires that the vein is optimal. If the vein is suspect or there are other good options for the creation of a new AVF, then the bypass may not be a good choice.
Arteriovenous Anastomotic and Juxta-Anastomotic Segment
Treatment
- A.
Angioplasty
- B.
Surgery:
- 1.
Redo the anastomosis.
- 2.
Patch angioplasty.
- 3.
Interposition graft.
- 1.
When treating a stenosis at the arteriovenous anastomosis, it appears that both operative intervention and balloon angioplasty are very successful.
Asif et al. reported on their success on treating 73 patients with an anastomotic stricture. A total of 112 percutaneous angioplasty procedures were performed with an early success rate of 97 %. Primary patency at 6 and 12 months was 75 % and 51 %, respectively. The secondary patency at 6 and 12 months was 94 % and 90 %, respectively [20].
Beathard et al. reported a 100 % success rate in the angioplasty of anastomotic stenosis [15].
The surgical approach to correction of a problem at the anastomosis includes redoing the anastomosis more proximal, patch angioplasty, or rarely placing an interposition bypass using vein or synthetic graft. Lee and colleagues looked at interventions on arteriovenous fistulas (AVFs) that were failing to mature and found that surgical interventions had better results than those treated with angioplasty. One-year primary patency for treatment of an immature fistula was 83 % for those treated operatively compared to 40 % of those treated with angioplasty [21]. Long and others similarly looked at surgical revision compared to angioplasty in the treatment of stenosis at anastomotic sites. They also found that surgical revision had better results. Primary patency at 1 year was 71 % with an operation verse 41 % with angioplasty [22].
In the review of these studies and others, both methods do work well with treating a stenosis at the anastomotic site [2, 3, 23, 24]. This leaves the treatment option to the discretion of the vascular access surgeon, along with the team of physicians caring for the patient, as to how they feel the patient should best be cared for.
Venous Outflow
- A.
Surgical:
- 1.
Ligate accessory or competing veins.
- 2.
Patch angioplasty.
- 3.
Provide new outflow.
- 1.
- B.
Percutaneous interventional approach:
- 1.
Coil embolization of accessory or competing veins
- 2.
Balloon-assisted maturation:
- (a)
Innovated idea, but does it work?
- (a)
- 3.
Stenosis
- 4.
Treat multiple areas
- 1.
There are a number of issues that are lumped into the category of having venous outflow problems. There are issues of accessory or competing veins, poor dilation of the main outflow vein, and poor outflow due to stenosis or occlusions. Accessory or competing veins to the main outflow vein have been described as reasons for fistulas not maturing. The incidence has been reported as high as 46 % [15]. In most studies it is not reported as a common problem, and the degree to which they contribute to poor maturation is hard to say. They are rarely an isolated reason for an arteriovenous fistula to not mature. Most often they are related to a significant stenosis or occlusion in the primary outflow vein more distal. When they are present, they can easily be treated with surgical ligation or percutaneous coil embolization.
On occasion, the outflow vein will not dilate. Miller and colleagues evaluated and treated 75 patients with an outflow vein measuring 2–5 mm in diameter. Their goal was to obtain dilation of the vein up to 6 mm. Repeat dilations every 3 weeks were performed until their goal of a 6 mm vein was met by ultrasound evaluation. The mean number of procedures to maturation was 2.6, and the mean time to maturation was 7 weeks. Primary patency at 6 months was 39 % with secondary patency of 77 % at 12 months, 61% at 24 months, and 32 % at 36 months [25]. Samett et al. also had success with balloon-assisted maturation of an AVF [26]. This is an innovative way of trying to get an arteriovenous fistula to mature. Additional studies are needed before it becomes a more routine means of assisting small veins to mature. If the outflow vein is truly small over its entire length, the traditional approach would be to consider abandoning the arteriovenous fistula.
Stenosis and/or occlusion of the outflow vein can again be treated both surgically and with angioplasty. There are some obvious situations where one is preferred over the other. In the case of short isolated areas of stenosis, especially if the areas of stenosis are located where it is difficult to access operatively, it makes sense to do balloon angioplasties. Very good success has been reported [1, 3, 15].
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