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Endovascular Management of the “Failing to Mature” Arteriovenous Fistula
Endovascular Management of the “Failing to Mature” Arteriovenous Fistula George M. Nassar, MD, FASN The “failing to mature” arteriovenous fistula (AVF) is frequently encountered among patients in need of hemodialysis (HD). It is essential that its prompt recognition and management are conducted in a timely manner to allow its use in HD. The physical examination is essential in early identification of the “failing to mature” AVF and helps guide initial endovascular management. In most instances, endovascular evaluation successfully identifies all the lesions that have contributed to AVF derangement and retarded its proper maturation. It is common to find juxta-arterial stenosis as well as venous stenosis in the body of the AVF, or its venous outflow tract. However, a wide spectrum of lesions can be seen, and in many instances, multiple lesions coexist in the same deranged AVF. Identifying and understanding the impact of all the lesions is a prerequisite for any intervention. Balloon angioplasty is the mainstay of management of stenotic lesions. Accessory vein obliteration or ligation is necessary in some cases. Procedure-related complications are low and are reduced by caution and experience. Overall, endovascular management is successful in converting the “failing to mature” AVF to usable HD access in the majority of cases, but multiple interventions may be needed in some before the AVF can be used for HD. Once usable, these AVFs have good long-term assisted patency rates. When endovascular management is unsuccessful or not possible, surgical revision of the AVF, or creation of a new AV vascular access is necessary. Tech Vasc Interventional Rad 11:175-180 © 2008 Elsevier Inc. All rights reserved.
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he “failing to mature” arteriovenous fistula (AVF) can be defined as a surgically created AVF that failed to properly grow to become usable for the purpose of hemodialysis (HD) in 8 to 12 weeks after its creation. Such failure is clinically manifest as difficult cannulation, inadequate AVF flow characteristics, or both. One may debate whether or not to include early AVF thrombosis in the category of “failing to mature” AVF. In support of such an inclusion is the fact that early AVF thrombosis has similar underlying derangements, and many could be salvaged using similar endovascular techniques. However, the term primary AVF failure clearly includes all causes of “failing to mature” AVF as well as early AVF thrombosis before any use.
Incidence The incidence of “failing to mature” AVF in the United States has increased in the recent decade. The increasing demand to
Department of Medicine, Weill Medical College of Cornell University, The Methodist Hospital, Houston, Texas; Renal Research, Inc., Houston, Texas; and Dialysis Access Management Centers, a division of Nephrology Dialysis and Transplantation Associates, The Kidney Institute, Houston, Texas. Address reprint requests to George M. Nassar, MD, FASN, The Kidney Institute, 1415 La Concha Lane, Houston, TX 77054. E-mail: geoamal@ sbcglobal.net.
1089-2516/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2008.09.004
create more fistulae has led to their creation in borderline vessels, thereby increasing primary failure rates to between 23 and 46%.1-8 Thus, understanding the underlying derangements and salvage of these primary failures will be essential for increasing AVF prevalence in the United States.
Pathology The “failing to mature” AVF is caused by intrinsically poor native vessels or by post surgical derangements. Poor native vessels relate to the utilization of a suboptimal artery or vein to create the AVF. It has been noted that arteries less than 1.5 to 2 mm and veins less than 2 to 2.5 mm in diameter are associated with poor AVF maturation.9-12 Extensive arterial atherosclerosis and preexisting venous stenosis, or even venous occlusion, are not uncommon derangements among studied cases of “failing to mature” AVF.13-16 The presence of accessory veins is another underlying derangement that is commonly seen. Most often it coexists with other venous outflow derangements that contributed to its growth, but in a minority of cases, it could be the sole cause of “failing to mature” AVF.15 Post surgical derangements are not necessarily errors and include a host of conditions such as narrow arterial anastomosis, juxta-arterial anastomosis stenosis, and emergence of venous stricture formation, especially in the cephalic vein arch and in surgically transposed veins. 175
G.M. Nassar
176 In a study15 of 119 patients who presented to our center with “failing to mature” AVF, multiple derangements were present in 85 (71.4%), while a single derangement was present in 34 (28.6%). Significant accessory veins were present in 35 (29.4%), but as the only cause of AVF dysfunction in 4 (3.4%). The frequencies of specific derangements were as follows: arterial stenosis 6 (5.1%), arterial anastomosis stenosis 56 (47.1%), juxta-arterial anastomosis stenosis 76 (63.9%), venous stenosis in either the body of the AVF or the venous outflow tract 70 (58.8%), and central vein stenosis 10 (8.4%). Six (5.0%) had neither stenosis nor accessory veins but could not be cannulated due to a deep AVF with varying degree of tortuosity.
Physical Examination The physical examination is very helpful in detecting AVF derangements.17,18 While this article is not intended to provide a thorough review of AVF examination, few points need to be stressed. The basic elements of physical examination, namely inspection, palpation, and auscultation, can easily depict AVF derangements, and in many instances, localize the type and location of derangement. For example, inspection may reveal superficial AVF branches that indicate the presence of accessory veins. Noticing an enlarging aneurysmal AVF segment close to the surgical incision indicates the presence of adjacent downstream venous stenosis. Palpation of a well-developing AVF reveals (1) smooth pulsations that quickly augment with occlusion of the AVF venous outflow tract, and (2) an easily palpable thrill, felt in both systole and diastole, detected over a long segment of the AVF. When both the pulsation and the thrill are weak, the AVF is referred to as “flat,” and this indicates poor inflow due to arterial disease or arterial anastomosis stenosis. On the other hand, strong and abrupt AVF pulsations indicate good arterial inflow but problematic venous stenosis. In these cases, the thrill is often limited only to systole, and the location of suspected venous stenosis may be accurately localized to an area in the AVF that corresponds to a transition in the intensity of pulsations from pounding strong to unequivocally weak. A high pitched bruit may be heard at this location. When such strong pulsation is limited only to the initial 5 cm from the arterial anastomosis of the AVF, it is referred to as water-hammer pulse and raises the suspicion of a juxta-arterial stenosis. A thrill that persists despite manual occlusion of the body of the AVF identifies the presence of significant upstream accessory veins. Such physical examination findings help recognition of AVF derangements and also direct the approach by the interventionalist during AVF salvage techniques.
Initial AVF Cannulation and Evaluation Approaching the “failing to mature” AVF is a delicate task due to immaturity of the vessels being intervened on. Very often, there is only a short and narrow segment that can be cannulated. This leaves low margin for error, and higher chance of AVF loss in the event of inadvertent vessel wall injury. Physical examination helps direct initial cannulation (Fig. 1). For suspicion of inflow stenosis, the needle is directed upstream
(toward the arterial anastomosis). For suspicion of outflow stenosis, the initial cannulation is directed downstream (toward the venous outflow). It is generally advised that cannulation be done using a 21-gauge needle that allows the introduction of a 0.018 inch guide wire over which a 5-F dilatorsheath is inserted and exchanged for a larger sheath if necessary. When initial cannulation is directed upstream, a guide wire is advanced to the arterial anastomosis and, if technically possible, it should be advanced upstream in the feeding artery. A 4- or 5-F infusion catheter is then advanced over the wire across the arterial anastomosis and an arteriogram and full antegrade fistulogram are obtained. This is the most ideal method to obtain the necessary images of the AVF and has the added advantage of evaluating distal arterial flow, which becomes important in cases of distal hypoperfusion syndromes. At times, however, the wire may not advance upstream in the feeding artery due to technical difficulties, and in such cases, one may derive the necessary images by injecting contrast as close to the arterial anastomosis as possible. Injecting contrast in the artery distal to the arterial anastomosis can be very helpful as some contrast often refluxes back to the AVF thereby outlining the arterial anastomosis and the initial segment of the AVF. It is noteworthy to mention that when initial cannulation is directed downstream, the arterial and juxta-arterial segments of the AVF can only be seen in a retrograde manner. While in many instances this retrograde approach provides sufficient information, it is a less desired method to evaluate the arterial inflow for several reasons: (1) it does not correspond to actual blood flow; (2) it may underestimate degree of stenosis; (3) it does not evaluate for vascular steal; and (4) it may completely fail to provide any information in the presence of upstream accessory veins. Its advantages however become manifest when intervening on a “failing to mature” AVF that has a very short segment amenable to cannulation where avoidance of a second cannulation is desired. Nevertheless, when necessary to derive more exact information, a second cannulation of the AVF, in an upstream orientation, should be done. In all instances, a full fistulogram should be performed and radiocontrast should be traced to the central veins. This allows identification of all vascular lesions contributing to failure of the AVF to mature. It is crucial to outline the anatomy of the arterial anastomosis and the juxta-arterial segment as these sites are frequently involved with stenotic lesions. In about 10% of referred cases of “failing to mature” AVF (personal experience), one needs to cannulate the brachial artery for full understanding of the AVF anatomy and flow dynamics, or to manage arterial stenosis.
Intervention The goal of intervention is to convert the “failing to mature” AVF to a usable access that lends itself to easy cannulation and provides enough blood flow to sustain HD. It is critical to understand the anatomy and flow dynamics of the AVF and identify all AVF-associated derangements before any intervention is initiated. This means one needs to evaluate the feeding artery, arterial anastomosis, juxta-arterial segment, body of the AVF (cannulation sites), accessory veins, venous outflow tract, and central veins.
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Figure 1 Flow diagram depicting general principles of initial diagnostic evaluation of “failing to mature” AVF.
Intervention usually involves balloon angioplasty of all significant vascular stenoses and obliteration of sizable accessory veins. A necessary requirement for balloon angioplasty is successful passage of a guide wire through the vessel requiring dilation. Angioplasty is attempted by gradually augmenting the balloon pressure by an insufflation device until it fully effaces. It is not uncommon for venous stenoses to require
inflation pressures up to 35 atm by using a Conquest angioplasty balloon (Bard Peripheral, Tempe, AZ). Much lower inflation pressures are generally used for arterial stenoses. In general, the angioplasty balloon used to dilate the arterial anastomosis is 4 to 5 mm in width, but a larger balloon is usually needed to dilate the juxta-arterial anastomosis and other venous segments. Care must be taken to avoid over
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to obliterate them. In most cases these accessory veins have grown in response to a downstream stenosis and dilating such stenosis would help the AVF grow despite the persistence of accessory veins. Large accessory veins, especially in the distal aspect of the AVF, are best ligated or obliterated. The latter entails selective cannulation of the vessel by a 5-F infusion catheter and the subsequent deployment of an intraluminal thrombogenic stainless steel coil. In all cases, a final antegrade fistulogram is obtained to determine technical success (Figs. 2-4).
Thrombosed AV Fistulae If the “failing to mature” AVF has already thrombosed, it may still be salvageable even though its chances of salvage decline.
Figure 2 Tight focal juxta-arterial anastomosis stenosis causing “water hammer” pulse, aneurysmal dilation of juxta-arterial segment, and failure of a brachio-cephalic AVF to mature. (A) Baseline fistulogram shows tight focal stenosis (white arrow) in the initial course of the AVF leading to aneurysmal dilation (arrowheads) of the juxtaarterial segment of the AVF. An accessory vein is present (black arrow). The brachial artery does not show in this image. Initial intervention is focused on traversing and dilating the tight focal stenosis. (B) A final angiogram is done after the intervention is complete, showing resolution of stenosis. In addition, the accessory vein was obliterated by deployment of thrombogenic coils (arrow). The aneurysmal dilation persists unchanged by angiography, but it is less tense by physical examination. This demonstrates that early intervention is of paramount importance in preventing progressive and irreversible aneurysmal formation induced by stenosis.
dilating the arterial anastomosis, thereby creating or aggravating vascular steal. Thus, a careful history of clinical symptoms of distal hypoperfusion would be helpful to obtain before the procedure. The accessory veins should also be the subject of decisions as to when to leave them alone and when
Figure 3 Complete venous tract occlusion causing development of accessory veins and failure of a radiocephalic AVF to mature. (A) Baseline fistulogram shows complete occlusion (white arrow) of the main radiocephalic vein in the mid forearm. Accessory and collateral veins (black arrows) have developed to provide alternate outflow tracts. Initial intervention is focused on traversing and dilating the occluded main radiocephalic vein. Traversing a complete occlusion is very challenging and at times may not be successful. (B) A final angiogram is done after the intervention is complete. In this case, there was successful dilation of the occluded radiocephalic vein. In addition, the accessory and collateral veins do not fill as blood is now flowing in the restored main radiocephalic vein, which is the path of least resistance. This is an example of resolution of accessory and collateral veins with successful angioplasty of the main venous outflow tract.
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Complications With careful technical skills, AVF loss is unusual with endovascular procedures but can occur. In our series,15 local hematoma formation occurred in about 15% of patients. These occurred at either the site of vessel cannulation or the angioplasty. In most cases, the hematoma was self-limiting and was contained simply with application of local pressure and conservative measures. Three patients had local pain and erythema around the site of accessory vein coil insertion, which subsided with conservative measures. In one patient, who also happened to have a deep AVF and is considered among the unsuccessful cases, vascular steal phenomenon worsened following intervention, and the AVF required elective ligation. None of the patients in our published series required endovascular stent placement to manage complications. It is however my advice that the interventionalist performing AVF salvage procedures be versed and equipped with the ability to place endovascular covered stents to manage AVF rupture that does not respond to conservative measures.
Short-Term Follow-Up and Outcomes
Figure 4 Tight juxta-arterial anastomosis stricture causing failure of a radiocephalic AVF to mature. (A) A radiocephalic AVF is “flat” by physical examination. It is a challenge to cannulate due to extreme immaturity. A catheter (white arrow) is advanced toward the arterial anastomosis where contrast in injected. Initial fistulogram shows strictured juxta-arterial anastomosis segment (black arrows). No flow is seen to the AVF, which is blocked by the mere presence of the 5-F infusion catheter. Contrast refluxes to the arterial system and outlines the radial artery (arrowheads). Initial intervention proceeds focusing on dilating the juxta-arterial segment and subsequently the rest of the AVF. (B) A final angiogram is done after the intervention is complete, showing resolution of juxta-arterial stenosis and prominence of blood flow to the AVF. An arterial anastomotic stenosis is revealed by this fistulogram (arrow). At times, this is difficult to reach from the AVF side due to the acute angle between the artery and the AVF. Intervention on this arterial lesion should be undertaken if clinically indicated. It may require direct cannulation of the arterial system to successfully reach and dilate it.
If the AVF or a segment of it is easily palpable by physical examination, or can be clearly outlined by ultrasound, then an attempt at declotting it should be undertaken (Fig. 1). The AVF thrombectomy procedure is described elsewhere.19,20 Thrombectomy should be followed by angioplasty of identified lesions. However, if the AVF is not palpable by physical examination, nor clearly outlined by ultrasonography, the procedure should not be attempted and the patient should be referred back to surgery for salvage of thrombosed AVF (low chances of success even with surgery), or creation of new AVF (hopefully following vascular mapping).
In most instances, the AVF needs additional time to mature following successful intervention. It is important to schedule a follow-up AVF physical examination in about 2 to 3 weeks following any intervention. The purpose is twofold: to inform the HD unit when the AVF can be used (in properly maturing cases), and to determine if additional endovascular intervention is necessary (in those with lack of improvement). During such subsequent intervention, one needs to reassess the status of the previous intervention and at the same time look for other derangements. For recurrent stenoses, angioplasty may need to be performed with a larger size balloon, and any sizable accessory veins left alone in the initial procedure may need to be obliterated. If an AVF fails to grow enough to be a suitable vascular access despite three separate endovascular interventions, one should consider surgical referral. Surgical referral may be best following first intervention if AVF-associated derangements could not be effectively treated. In our series,15 repeat intervention was necessary in about 25% of patients due to lack of clinical improvement as judged by physical examination. Ultimately, about 83% of fistulae became usable for HD. A summary of the reasons for failure of AVF salvage is provided in Table 1.
Long-Term Patency Rates Long-term follow-up of “failing to mature” fistulae that become usable for HD is reassuring. While these AVFs will require repeat procedures to maintain patency, they overall undergo low attrition rates. Again, referring to our own series,15 during a period of 882 patient-months of follow-up, there were a total of 11 deaths and three kidney transplants in patients whose salvaged AVF was still functioning. Only 3 patients lost their AVF due to thrombosis, and 17 required a total of 25 repeat endovascular treatments for angioplasty or thrombectomy. The total AVF event rate was 0.38/access-
G.M. Nassar
180 Table 1 Reasons for Unsuccessful Endovascular Procedures in Management of “Failing to Mature” AVF AVF Outflow Problems: —Occlusion of venous outflow tract that cannot be traversed by guide wire —Long stricture of venous outflow tract that does not respond to angioplasty AVF Inflow Problems: —Diffusely narrow and atherosclerotic feeding artery limiting flow to AVF —Narrow arterial anastomosis that is not amenable to dilatation due to narrow artery —Strictured, tortuous, or occluded juxta-arterial anastomotic segment that cannot be traversed by guide wire, or does not respond to angioplasty Other Anatomic Problems: —Deep and tortuous AVF that poses cannulation difficulty despite adequate flow —Extensive multiple accessory veins in the context of narrow main AVF venous tract
year, AVF thrombosis rate was 0.12/access-year, and AVF loss rate was 0.04/access-year.
Concluding Remarks Endovascular treatment, by experienced interventionalists, is both safe and effective in managing the “failing to mature” AVF. It does not eliminate the need for additional vascular surgery in some patients. However, its advantages as first-line therapy include the following: (1) it is associated with excellent success rates, low complication rates, and promising long-term patency rates14-16; (2) it is done without the introduction and assistance of synthetic jump polytetrafluoroethylene (PTFE) grafts; (3) it uncovers all the contributing lesions to AVF dysfunction. Such information is valuable and is the basis for any successful treatment approach including surgical revision. In other instances, it may mean totally abandoning the existing AVF and saving the patient from unnecessary procedures or surgical revision. Repeat procedures may be necessary to further assist the “failing to mature” AVF, or to maintain its patency subsequent to its use in HD. Overall, salvaged AVFs have good long-term assisted patency rates.
Acknowledgments This work was supported in part by Renal Research, Inc.
References 1. Allon M, Robbin ML: Increasing arteriovenous fistulas in hemodialysis patients: problems and solutions. Kidney Int 62:1109-1124, 2002 2. Miller CD, Robbin ML, Allon M: Gender differences in outcomes of arteriovenous fistulas in hemodialysis patients. Kidney Int 63:346-352, 2003 3. Rao RK, Azin GD, Hood DB, et al: Basilic vein transposition fistula: a good option for maintaining hemodialysis access site options? J Vasc Surg 39:1043-1047, 2004 4. Dixon BS, Novak L, Fangman J: Hemodialysis vascular access survival: the upper arm native arteriovenous fistula. Am J Kidney Dis 39:92-101, 2002 5. Lok CE, Oliver MJ, Su J, et al: Arteriovenous fistula outcomes in the era of the elderly dialysis population. Kidney Int 67:2462-2469, 2005 6. Oliver MJ, McCann RL, Indridason OS, et al: Comparison of transposed brachiobasilic fistulas to upper arm grafts and brachiocephalic fistulas. Kidney Int 60:1532-1539, 2001 7. Miller PE, Tolwani A, Luscy CP, et al: Predictors of adequacy of arteriovenous fistulas in hemodialysis patients. Kidney Int 56:275-280, 1999 8. Patel ST, Hughes J, Mills JL Sr: Failure of arteriovenous fistula maturation: an unintended consequence of exceeding dialysis outcome quality initiative guidelines for hemodialysis access. J Vasc Surg 38:439-445, 2003 9. Brimble KS, Rabbat CG, Schiff D, et al: The clinical utility of Doppler ultrasound prior to arteriovenous fistula creation. Semin Dial 14:314317, 2001 10. Malovrh M: Native arteriovenous fistula: preoperative evaluation. Am J Kidney Dis 39:1218-1225, 2002 11. Parmar J, Aslam M, Standfield N: Pre-operative radial arterial diameter predicts early failure of arteriovenous fistula (AVF) for hemodialysis. Eur J Vasc Endocasc Surg 33:113-115, 2007 12. Silva MB Jr, Hobson RW 2nd, Pappas PJ, et al: A strategy for increasing use of autogenous hemodialysis access procedures: impact of preoperative noninvasive evaluation. J Vasc Surg 27:302-308, 1998 13. Beathard GA, Settle SM, Shields MW: Salvage of poorly developed arteriovenous fistulae. Am J Kidney Dis 33:910-916, 1999 14. Beathard GA, Arnold P, Jackson J, et al: Aggressive treatment of early fistula failure. Kidney Int 64:1487-1494, 2003 15. Nassar GM, Nguyen B, Rhee E, et al: Endovascular treatment of the “failing to mature” arteriovenous fistula. Clin J Am Soc Nephrol 1:275280, 2006 16. Turmel-Rodrigues L, Mouton A, Birmele B, et al: Salvage of immature fistulas of haemodialysis by interventional radiology. Nephrol Dial Transplant 16:2365-2371, 2001 17. Beathard GA: Physical examination of the dialysis vascular access. Semin Dial 11:231-236, 1998 18. Beathard GA: Physical examination: the forgotten tool, in Gray R, Sands J (eds): A Multidisciplinary Approach for Hemodialysis Access. New York, NY, Lippincott Williams & Wilkins, 2002, pp 111-118 19. Schon D, Mishler R: Pharmacomechanical thrombolysis of natural vein fistulas: reduced dose of TPA and long-term follow-up. Semin Dial 16:272-275, 2003 20. Nassar GM: What should nephrologists do to maximize the use of AVFs. Semin Dial 19:207-209, 2006
T
he “failing to mature” arteriovenous fistula (AVF) can be defined as a surgically created AVF that failed to properly grow to become usable for the purpose of hemodialysis (HD) in 8 to 12 weeks after its creation. Such failure is clinically manifest as difficult cannulation, inadequate AVF flow characteristics, or both. One may debate whether or not to include early AVF thrombosis in the category of “failing to mature” AVF. In support of such an inclusion is the fact that early AVF thrombosis has similar underlying derangements, and many could be salvaged using similar endovascular techniques. However, the term primary AVF failure clearly includes all causes of “failing to mature” AVF as well as early AVF thrombosis before any use.
Incidence The incidence of “failing to mature” AVF in the United States has increased in the recent decade. The increasing demand to
Department of Medicine, Weill Medical College of Cornell University, The Methodist Hospital, Houston, Texas; Renal Research, Inc., Houston, Texas; and Dialysis Access Management Centers, a division of Nephrology Dialysis and Transplantation Associates, The Kidney Institute, Houston, Texas. Address reprint requests to George M. Nassar, MD, FASN, The Kidney Institute, 1415 La Concha Lane, Houston, TX 77054. E-mail: geoamal@ sbcglobal.net.
1089-2516/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2008.09.004
create more fistulae has led to their creation in borderline vessels, thereby increasing primary failure rates to between 23 and 46%.1-8 Thus, understanding the underlying derangements and salvage of these primary failures will be essential for increasing AVF prevalence in the United States.
Pathology The “failing to mature” AVF is caused by intrinsically poor native vessels or by post surgical derangements. Poor native vessels relate to the utilization of a suboptimal artery or vein to create the AVF. It has been noted that arteries less than 1.5 to 2 mm and veins less than 2 to 2.5 mm in diameter are associated with poor AVF maturation.9-12 Extensive arterial atherosclerosis and preexisting venous stenosis, or even venous occlusion, are not uncommon derangements among studied cases of “failing to mature” AVF.13-16 The presence of accessory veins is another underlying derangement that is commonly seen. Most often it coexists with other venous outflow derangements that contributed to its growth, but in a minority of cases, it could be the sole cause of “failing to mature” AVF.15 Post surgical derangements are not necessarily errors and include a host of conditions such as narrow arterial anastomosis, juxta-arterial anastomosis stenosis, and emergence of venous stricture formation, especially in the cephalic vein arch and in surgically transposed veins. 175
G.M. Nassar
176 In a study15 of 119 patients who presented to our center with “failing to mature” AVF, multiple derangements were present in 85 (71.4%), while a single derangement was present in 34 (28.6%). Significant accessory veins were present in 35 (29.4%), but as the only cause of AVF dysfunction in 4 (3.4%). The frequencies of specific derangements were as follows: arterial stenosis 6 (5.1%), arterial anastomosis stenosis 56 (47.1%), juxta-arterial anastomosis stenosis 76 (63.9%), venous stenosis in either the body of the AVF or the venous outflow tract 70 (58.8%), and central vein stenosis 10 (8.4%). Six (5.0%) had neither stenosis nor accessory veins but could not be cannulated due to a deep AVF with varying degree of tortuosity.
Physical Examination The physical examination is very helpful in detecting AVF derangements.17,18 While this article is not intended to provide a thorough review of AVF examination, few points need to be stressed. The basic elements of physical examination, namely inspection, palpation, and auscultation, can easily depict AVF derangements, and in many instances, localize the type and location of derangement. For example, inspection may reveal superficial AVF branches that indicate the presence of accessory veins. Noticing an enlarging aneurysmal AVF segment close to the surgical incision indicates the presence of adjacent downstream venous stenosis. Palpation of a well-developing AVF reveals (1) smooth pulsations that quickly augment with occlusion of the AVF venous outflow tract, and (2) an easily palpable thrill, felt in both systole and diastole, detected over a long segment of the AVF. When both the pulsation and the thrill are weak, the AVF is referred to as “flat,” and this indicates poor inflow due to arterial disease or arterial anastomosis stenosis. On the other hand, strong and abrupt AVF pulsations indicate good arterial inflow but problematic venous stenosis. In these cases, the thrill is often limited only to systole, and the location of suspected venous stenosis may be accurately localized to an area in the AVF that corresponds to a transition in the intensity of pulsations from pounding strong to unequivocally weak. A high pitched bruit may be heard at this location. When such strong pulsation is limited only to the initial 5 cm from the arterial anastomosis of the AVF, it is referred to as water-hammer pulse and raises the suspicion of a juxta-arterial stenosis. A thrill that persists despite manual occlusion of the body of the AVF identifies the presence of significant upstream accessory veins. Such physical examination findings help recognition of AVF derangements and also direct the approach by the interventionalist during AVF salvage techniques.
Initial AVF Cannulation and Evaluation Approaching the “failing to mature” AVF is a delicate task due to immaturity of the vessels being intervened on. Very often, there is only a short and narrow segment that can be cannulated. This leaves low margin for error, and higher chance of AVF loss in the event of inadvertent vessel wall injury. Physical examination helps direct initial cannulation (Fig. 1). For suspicion of inflow stenosis, the needle is directed upstream
(toward the arterial anastomosis). For suspicion of outflow stenosis, the initial cannulation is directed downstream (toward the venous outflow). It is generally advised that cannulation be done using a 21-gauge needle that allows the introduction of a 0.018 inch guide wire over which a 5-F dilatorsheath is inserted and exchanged for a larger sheath if necessary. When initial cannulation is directed upstream, a guide wire is advanced to the arterial anastomosis and, if technically possible, it should be advanced upstream in the feeding artery. A 4- or 5-F infusion catheter is then advanced over the wire across the arterial anastomosis and an arteriogram and full antegrade fistulogram are obtained. This is the most ideal method to obtain the necessary images of the AVF and has the added advantage of evaluating distal arterial flow, which becomes important in cases of distal hypoperfusion syndromes. At times, however, the wire may not advance upstream in the feeding artery due to technical difficulties, and in such cases, one may derive the necessary images by injecting contrast as close to the arterial anastomosis as possible. Injecting contrast in the artery distal to the arterial anastomosis can be very helpful as some contrast often refluxes back to the AVF thereby outlining the arterial anastomosis and the initial segment of the AVF. It is noteworthy to mention that when initial cannulation is directed downstream, the arterial and juxta-arterial segments of the AVF can only be seen in a retrograde manner. While in many instances this retrograde approach provides sufficient information, it is a less desired method to evaluate the arterial inflow for several reasons: (1) it does not correspond to actual blood flow; (2) it may underestimate degree of stenosis; (3) it does not evaluate for vascular steal; and (4) it may completely fail to provide any information in the presence of upstream accessory veins. Its advantages however become manifest when intervening on a “failing to mature” AVF that has a very short segment amenable to cannulation where avoidance of a second cannulation is desired. Nevertheless, when necessary to derive more exact information, a second cannulation of the AVF, in an upstream orientation, should be done. In all instances, a full fistulogram should be performed and radiocontrast should be traced to the central veins. This allows identification of all vascular lesions contributing to failure of the AVF to mature. It is crucial to outline the anatomy of the arterial anastomosis and the juxta-arterial segment as these sites are frequently involved with stenotic lesions. In about 10% of referred cases of “failing to mature” AVF (personal experience), one needs to cannulate the brachial artery for full understanding of the AVF anatomy and flow dynamics, or to manage arterial stenosis.
Intervention The goal of intervention is to convert the “failing to mature” AVF to a usable access that lends itself to easy cannulation and provides enough blood flow to sustain HD. It is critical to understand the anatomy and flow dynamics of the AVF and identify all AVF-associated derangements before any intervention is initiated. This means one needs to evaluate the feeding artery, arterial anastomosis, juxta-arterial segment, body of the AVF (cannulation sites), accessory veins, venous outflow tract, and central veins.
Management of “failing to mature” AVF
177
Figure 1 Flow diagram depicting general principles of initial diagnostic evaluation of “failing to mature” AVF.
Intervention usually involves balloon angioplasty of all significant vascular stenoses and obliteration of sizable accessory veins. A necessary requirement for balloon angioplasty is successful passage of a guide wire through the vessel requiring dilation. Angioplasty is attempted by gradually augmenting the balloon pressure by an insufflation device until it fully effaces. It is not uncommon for venous stenoses to require
inflation pressures up to 35 atm by using a Conquest angioplasty balloon (Bard Peripheral, Tempe, AZ). Much lower inflation pressures are generally used for arterial stenoses. In general, the angioplasty balloon used to dilate the arterial anastomosis is 4 to 5 mm in width, but a larger balloon is usually needed to dilate the juxta-arterial anastomosis and other venous segments. Care must be taken to avoid over
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to obliterate them. In most cases these accessory veins have grown in response to a downstream stenosis and dilating such stenosis would help the AVF grow despite the persistence of accessory veins. Large accessory veins, especially in the distal aspect of the AVF, are best ligated or obliterated. The latter entails selective cannulation of the vessel by a 5-F infusion catheter and the subsequent deployment of an intraluminal thrombogenic stainless steel coil. In all cases, a final antegrade fistulogram is obtained to determine technical success (Figs. 2-4).
Thrombosed AV Fistulae If the “failing to mature” AVF has already thrombosed, it may still be salvageable even though its chances of salvage decline.
Figure 2 Tight focal juxta-arterial anastomosis stenosis causing “water hammer” pulse, aneurysmal dilation of juxta-arterial segment, and failure of a brachio-cephalic AVF to mature. (A) Baseline fistulogram shows tight focal stenosis (white arrow) in the initial course of the AVF leading to aneurysmal dilation (arrowheads) of the juxtaarterial segment of the AVF. An accessory vein is present (black arrow). The brachial artery does not show in this image. Initial intervention is focused on traversing and dilating the tight focal stenosis. (B) A final angiogram is done after the intervention is complete, showing resolution of stenosis. In addition, the accessory vein was obliterated by deployment of thrombogenic coils (arrow). The aneurysmal dilation persists unchanged by angiography, but it is less tense by physical examination. This demonstrates that early intervention is of paramount importance in preventing progressive and irreversible aneurysmal formation induced by stenosis.
dilating the arterial anastomosis, thereby creating or aggravating vascular steal. Thus, a careful history of clinical symptoms of distal hypoperfusion would be helpful to obtain before the procedure. The accessory veins should also be the subject of decisions as to when to leave them alone and when
Figure 3 Complete venous tract occlusion causing development of accessory veins and failure of a radiocephalic AVF to mature. (A) Baseline fistulogram shows complete occlusion (white arrow) of the main radiocephalic vein in the mid forearm. Accessory and collateral veins (black arrows) have developed to provide alternate outflow tracts. Initial intervention is focused on traversing and dilating the occluded main radiocephalic vein. Traversing a complete occlusion is very challenging and at times may not be successful. (B) A final angiogram is done after the intervention is complete. In this case, there was successful dilation of the occluded radiocephalic vein. In addition, the accessory and collateral veins do not fill as blood is now flowing in the restored main radiocephalic vein, which is the path of least resistance. This is an example of resolution of accessory and collateral veins with successful angioplasty of the main venous outflow tract.
Management of “failing to mature” AVF
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Complications With careful technical skills, AVF loss is unusual with endovascular procedures but can occur. In our series,15 local hematoma formation occurred in about 15% of patients. These occurred at either the site of vessel cannulation or the angioplasty. In most cases, the hematoma was self-limiting and was contained simply with application of local pressure and conservative measures. Three patients had local pain and erythema around the site of accessory vein coil insertion, which subsided with conservative measures. In one patient, who also happened to have a deep AVF and is considered among the unsuccessful cases, vascular steal phenomenon worsened following intervention, and the AVF required elective ligation. None of the patients in our published series required endovascular stent placement to manage complications. It is however my advice that the interventionalist performing AVF salvage procedures be versed and equipped with the ability to place endovascular covered stents to manage AVF rupture that does not respond to conservative measures.
Short-Term Follow-Up and Outcomes
Figure 4 Tight juxta-arterial anastomosis stricture causing failure of a radiocephalic AVF to mature. (A) A radiocephalic AVF is “flat” by physical examination. It is a challenge to cannulate due to extreme immaturity. A catheter (white arrow) is advanced toward the arterial anastomosis where contrast in injected. Initial fistulogram shows strictured juxta-arterial anastomosis segment (black arrows). No flow is seen to the AVF, which is blocked by the mere presence of the 5-F infusion catheter. Contrast refluxes to the arterial system and outlines the radial artery (arrowheads). Initial intervention proceeds focusing on dilating the juxta-arterial segment and subsequently the rest of the AVF. (B) A final angiogram is done after the intervention is complete, showing resolution of juxta-arterial stenosis and prominence of blood flow to the AVF. An arterial anastomotic stenosis is revealed by this fistulogram (arrow). At times, this is difficult to reach from the AVF side due to the acute angle between the artery and the AVF. Intervention on this arterial lesion should be undertaken if clinically indicated. It may require direct cannulation of the arterial system to successfully reach and dilate it.
If the AVF or a segment of it is easily palpable by physical examination, or can be clearly outlined by ultrasound, then an attempt at declotting it should be undertaken (Fig. 1). The AVF thrombectomy procedure is described elsewhere.19,20 Thrombectomy should be followed by angioplasty of identified lesions. However, if the AVF is not palpable by physical examination, nor clearly outlined by ultrasonography, the procedure should not be attempted and the patient should be referred back to surgery for salvage of thrombosed AVF (low chances of success even with surgery), or creation of new AVF (hopefully following vascular mapping).
In most instances, the AVF needs additional time to mature following successful intervention. It is important to schedule a follow-up AVF physical examination in about 2 to 3 weeks following any intervention. The purpose is twofold: to inform the HD unit when the AVF can be used (in properly maturing cases), and to determine if additional endovascular intervention is necessary (in those with lack of improvement). During such subsequent intervention, one needs to reassess the status of the previous intervention and at the same time look for other derangements. For recurrent stenoses, angioplasty may need to be performed with a larger size balloon, and any sizable accessory veins left alone in the initial procedure may need to be obliterated. If an AVF fails to grow enough to be a suitable vascular access despite three separate endovascular interventions, one should consider surgical referral. Surgical referral may be best following first intervention if AVF-associated derangements could not be effectively treated. In our series,15 repeat intervention was necessary in about 25% of patients due to lack of clinical improvement as judged by physical examination. Ultimately, about 83% of fistulae became usable for HD. A summary of the reasons for failure of AVF salvage is provided in Table 1.
Long-Term Patency Rates Long-term follow-up of “failing to mature” fistulae that become usable for HD is reassuring. While these AVFs will require repeat procedures to maintain patency, they overall undergo low attrition rates. Again, referring to our own series,15 during a period of 882 patient-months of follow-up, there were a total of 11 deaths and three kidney transplants in patients whose salvaged AVF was still functioning. Only 3 patients lost their AVF due to thrombosis, and 17 required a total of 25 repeat endovascular treatments for angioplasty or thrombectomy. The total AVF event rate was 0.38/access-
G.M. Nassar
180 Table 1 Reasons for Unsuccessful Endovascular Procedures in Management of “Failing to Mature” AVF AVF Outflow Problems: —Occlusion of venous outflow tract that cannot be traversed by guide wire —Long stricture of venous outflow tract that does not respond to angioplasty AVF Inflow Problems: —Diffusely narrow and atherosclerotic feeding artery limiting flow to AVF —Narrow arterial anastomosis that is not amenable to dilatation due to narrow artery —Strictured, tortuous, or occluded juxta-arterial anastomotic segment that cannot be traversed by guide wire, or does not respond to angioplasty Other Anatomic Problems: —Deep and tortuous AVF that poses cannulation difficulty despite adequate flow —Extensive multiple accessory veins in the context of narrow main AVF venous tract
year, AVF thrombosis rate was 0.12/access-year, and AVF loss rate was 0.04/access-year.
Concluding Remarks Endovascular treatment, by experienced interventionalists, is both safe and effective in managing the “failing to mature” AVF. It does not eliminate the need for additional vascular surgery in some patients. However, its advantages as first-line therapy include the following: (1) it is associated with excellent success rates, low complication rates, and promising long-term patency rates14-16; (2) it is done without the introduction and assistance of synthetic jump polytetrafluoroethylene (PTFE) grafts; (3) it uncovers all the contributing lesions to AVF dysfunction. Such information is valuable and is the basis for any successful treatment approach including surgical revision. In other instances, it may mean totally abandoning the existing AVF and saving the patient from unnecessary procedures or surgical revision. Repeat procedures may be necessary to further assist the “failing to mature” AVF, or to maintain its patency subsequent to its use in HD. Overall, salvaged AVFs have good long-term assisted patency rates.
Acknowledgments This work was supported in part by Renal Research, Inc.
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