Reporting Standards for Percutaneous Interventions in Dialysis Access

Feasibility of trans-radial approach in percutaneous intervention for upper arm dialysis access

BACKGROUND

This retrospective study evaluated the feasibility and efficacy of trans-radial intervention for upper arm dialysis access.

METHODS

This study retrospectively reviewed 165 trans-radial interventions performed for upper arm dialysis access in 101 patients. Sixty-nine patients had arteriovenous graft (AVG), and 32 had arteriovenous fistula (AVF). Balloon angioplasty was performed in 66 stenotic dialysis accesses and 99 thrombosed dialysis accesses. Thrombosed dialysis access was further managed by additional balloon thrombectomy with or without urokinase injection.

RESULTS

Procedural time was 46.7 +/- 25.5 minutes. Anatomic and clinical success rates were 89.7% and 84.2%, respectively. The rate of complications, most of which involved lesion rupture with contrast-media extravasation and distal embolism, was 9.7%. Pretreatment stenosis was more severe (p = 0.01) and the prevalence of total occlusion was higher (p < 0.01) in the AVG group than the AVF group. The success rate and complication rate did not statistically differ (p = 0.59). Additionally, the thrombosed group had a lower success rate (p = 0.02), a higher complication rate (p < 0.01) and a longer procedural time (p < 0.01) than the stenotic group.

CONCLUSIONS

Comparison with previous studies employing the traditional approach reveals that trans-radial intervention has a comparable success rate, procedural time and complication rate for upper arm dialysis access. Therefore, trans-radial intervention is a safe and feasible technique for upper arm dialysis access.

[Management of perianastomotic stenoses complicating vascular accesses for haemodialysis]

OBJECTIVE

Perianastomotic stenoses (PAS) complicating native arteriovenous fistulas (AVF) of the forearm can be treated by angioplasty or surgery. The objective of this study was to report primary patency (PP) and primary assisted patency (PAP) rates of surgery and angioplasty of these stenoses. The secondary objective was to identify factors influencing the patency rates of these reoperations.

MATERIAL AND METHODS

Seventy-three patients with a mean age, 65 years were treated for PAS between January 1999 and December 2005 in two centres (Tours and Le Mans), which were retrospectively included. PAS were treated by surgery (n=21) or angioplasty (n=52). The two groups were comparable. The mean follow-up was 39 months for the angioplasty group and 49 months for the surgery group (p=0.088).

RESULTS

The PP rate was 71+/-10% for surgery and 41+/-6% for angioplasty (p<0.0175). The PAP rate was not significantly different (p=0.462) between angioplasty (92+/-4%) and surgery (95+/-4%). In the endovascular group, the site of stenosis on the anastomosis was a risk factor for early recurrence (95% CI between 0.006 and 0.392; p=0.047).

CONCLUSION

These results suggest that anastomotic stenoses should be treated surgically rather than by angioplasty. Angioplasty and surgery give identical patency rates in other types of perianastomotic stenoses at the cost of a higher reoperation rate for angioplasty.

Stent placement versus angioplasty improves patency of arteriovenous grafts and blood flow of arteriovenous fistulae

BACKGROUND

While endovascular stent placement is the standard of care in most percutaneous coronary and peripheral artery intervention, its role in the salvage of thrombosed and stenotic hemodialysis access remains controversial.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

We compared the effects of stent versus angioplasty on primary patency rates in the treatment of stenotic arteriovenous fistulae (AVF) and arteriovenous grafts (AVGs). Moreover, we compared access flow (Qa) and urea reduction ratio (URR) between the two groups as a metric of the effect of stent placement versus angioplasty on dialysis delivery.

RESULTS

Cox regression analysis revealed that the primary assisted AVG patency was significantly longer for the stent group compared with angioplasty, with a median survival of 138 versus 61 d, respectively (aHR = 0.17; 95% confidence interval, 0.07 to 0.39; P < 0.001). The primary AVG patency for stent versus angioplasty was 91% versus 80% at 30 d, 69% versus 24% at 90 d, and 25% versus 3% at 180 d, respectively. The primary assisted AVF patency did not differ significantly between the stent and angioplasty groups. In patients dialyzing via AVF, multiple regression analysis revealed that stent placement was associated with improved after intervention peak Qa, 1627.50 ml/min versus 911.00 ml/min (beta = 0.494; P = 0.008), change in Qa from before to after intervention, 643.54 ml/min versus 195.35 ml/min (beta = 0.464; P = 0.012), and change in URR from before to after intervention, 5.85% versus 0.733% (beta = 0.389; P = 0.039).

CONCLUSIONS

Our results suggest that stent placement is associated with improved AVG primary assisted patency and improved AVF blood flow, which may significantly impact on dialysis adequacy.

Non-Surgical Salvage of Thrombosed Arterio-Venous Fistulae: A Case Series and Review of the Literature

Attempts to salvage thrombosed hemodialysis arterio-venous fistulae (AVF) using interventional techniques are not universally performed. Patients often require temporary dialysis catheters pending creation of a new vascular access. We determined the long-term outcome of interventional (non-surgical) repair of completely thrombosed AVF in 49 consecutive accesses (22 radio-cephalic, 1 radio-basilic, 19 brachio-cephalic, and 7 brachio-basilic) referred for an intervention within 48 hours of thrombosis. Subjects were 65% male (32), with mean +/- SD age 63.7 +/- 13.5 years (range 33-91), 51% African-American (25), 47% Caucasian (23) and 65% had diabetes (32). Overall, 96% (47/49) of thrombosed AVF were salvaged with complications observed in four cases (two extravasations of contrast; two radial artery emboli), with no serious long-term sequelae. Interventional procedures included 34 venous angioplasties, 11 venous angioplasties with stenting and two combined venous and arterial angioplasties. The primary and secondary patency rates for all salvaged AVF were 50.5 +/- 8.7%, 72.5 +/- 7.8% at 1 year, and 43.3 +/- 10%, 55.4 +/- 12.7% at 2 years, respectively. The median estimate to first intervention after the declot procedure was 14.7 months. The median estimate for continued function exceeded 23.1 months. There was no significant statistical difference in the primary (p = 0.73) and secondary patency rates (p = 0.057) for forearm vs. upper arm AVF. We conclude that interventional repairs should routinely be employed to salvage newly thrombosed AVF. The vast majority of these individuals can avoid receiving dialysis catheters or placement of a new dialysis vascular access.

Angioplasty of Long Venous Stenoses in Hemodialysis Access: At Last an Indication for Cutting Balloon?

PURPOSE

To compare the postintervention primary patency rates of cutting balloon angioplasty (CBA) with those of conventional percutaneous transluminal angioplasty (PTA) in the treatment of hemodialysis-related stenoses at least 2 cm long.

MATERIALS AND METHODS

This retrospective and controlled study included 29 patients with a hemodialysis-related stenosis at least 2 cm long. From August 2002 to August 2003, nine patients (PTA group, six upper-arm and three forearm fistulas) were treated with a conventional balloon (5-8 mm, 4 cm long). From September 2003 to December 2005, 20 patients (CBA group, 12 upper-arm and seven forearm fistulas; one polytetrafluoroethylene hemodialysis graft) were treated with a cutting balloon (5-7 mm, 1 cm long). The median follow-up was 22.1 months for the CBA group and 15.6 months for the PTA group. The Kaplan-Meier method was used to calculate the primary cumulative patency rates, and the log-rank test was used for comparison. Multivariate Cox models were generated by combining three variables: patient age, stenosis length, and treatment type (CBA or PTA).

RESULTS

In the CBA group, the postintervention primary patency was 85% +/- 16 at 6 months, 70% +/- 20 at 1 year, and 32% +/- 26 at 18 months. In the PTA group, the postintervention primary patency was 56% +/- 32 at 6 months and 21% (range, 0%-53%) at 1 year. When comparing PTA versus CBA with the log-rank test, there was a statistically significant difference (P = .009). With the multivariate Cox models, treatment was again a statistically significant (P = .007) determinant of primary patency; patient age and stenosis length were not.

CONCLUSION

The use of a cutting balloon as the first-line treatment for stenoses at least 2 cm long significantly improves the postintervention primary patency rate.

Classification of Complications Associated with Hemodialysis Vascular Access Procedures: A Position Statement from the American Society of Diagnostic and Interventional Nephrology

A procedure-related complication is an unanticipated adverse event that requires therapy. In order to analyze frequency and severity of complications in the process of quality assurance, it is useful to have a classification of complications, indicating the type and severity. The Clinical Practice Committee of American Society of Diagnostic and Interventional Nephrology has developed a Classification of Complications relating to Hemodialysis Vascular Access Procedures, based on the system first proposed by Beathard in 2006. In this system, the "type" refers to the procedure being performed or vessel entered, and the "grade" is based on the intensity of medical care needed to address the complication. This publication describes 10 Types and 4 Grades of complications.

Bidirectional angioplasty with single vascular access in autogenous arteriovenous fistula

PURPOSE

In autogenous arteriovenous (AV) fistulas with multiple stenoses at extreme ends, one option for treatment of the stenoses with angioplasty is dual access directed toward both ends of the fistula. The present study is a retrospective evaluation of experiences with an alternative access technique, bidirectional angioplasty with a single vascular access.

MATERIALS AND METHODS

A total of 124 bidirectional angioplasty procedures with a single vascular access performed in 96 autogenous AV fistulas (48 men and 48 women; mean age, 58 years) were evaluated. After fistulography, a dilated segment of the draining vein located between the proximal and distal stenoses, with its course straight or convex toward the interventional radiologist, was punctured with an 18-gauge needle. The needle was directed antegrade and an introducer sheath was inserted for angioplasty of the proximal or central venous stenoses. Then, with a safety guide wire in place, the introducer sheath was withdrawn and redirected retrograde for angioplasty of the distal stenoses.

RESULTS

Technical success rates of redirection of the introducer sheath and angioplasty were 100% and 96.8%, respectively. The failures of angioplasty were related to elastic recoil (n = 3) and inability to pass the guide wire through an occluded distal vein (n = 1). Overall procedure times were 7-70 minutes (mean, 31 min). One pseudoaneurysm was the only access-related complication.

CONCLUSIONS

Bidirectional angioplasty with a single vascular access is a feasible method of access in angioplasty of autogenous AV fistulas with stenoses at extreme ends.

Percutaneous Interventions in Subclavian Artery–to–Contralateral Subclavian Vein “Necklace” Hemodialysis Grafts: Experience in Five Patients

PURPOSE

To describe clinical outcomes of endovascular interventions in the setting of thrombosis or dysfunction of anterior chest wall ("necklace") arteriovenous (AV) hemodialysis grafts.

MATERIALS AND METHODS

Eight percutaneous interventions (balloon angioplasty, pharmacologic thrombolysis, and mechanical thrombectomy) were performed in five patients with anterior chest wall AV grafts. Primary, assisted, and secondary patencies, as well as technical success and complication rates, were determined.

RESULTS

The technical success rate of percutaneous interventions in re-establishing a normal blood flow pattern within the AV grafts was 100%. Primary patency ranged from one to 23 months (median, 5 months). Primary assisted patency and secondary patency were 36 months and 8 months, respectively, in two patients who underwent more than one intervention. Postintervention access patency ranged from 5 to 36 months (median, 9 months), whereas graft lifetime ranged from 12 to 45 months (median, 24 months). There were no complications related to revascularization procedures.

CONCLUSION

Percutaneous interventions can be performed safely and effectively in anterior chest wall AV grafts. Technical success and long-term patency rates appear to be similar to those of percutaneous interventions in upper-extremity hemodialysis AV grafts.

BRAVO I: A pilot study of vascular brachytherapy in polytetrafluoroethylene dialysis access grafts

Hemodialysis vascular access dysfunction owing to stenosis and thrombosis in polytetrafluoroethylene dialysis access grafts is a huge clinical problem for which there are currently no long lasting durable therapies. Vascular brachytherapy has been used successfully for the prevention of coronary restenosis following angioplasty and stent placement. The Beta Radiation for Treatment of Arterial-Venous Graft Outflow I study was a pilot study of vascular brachytherapy in hemodialysis patients with patent but dysfunctional grafts. Twenty-five patients were randomized to receive either radiation therapy (a single dose of 18.4 Gy) or sham radiation, following angioplasty. The primary efficacy end point of the study was target lesion primary patency at 6 months. The primary safety end point was a composite of death, emergency surgery on the graft, venous rupture, or aneurysm formation. Forty-two percent of the radiated grafts achieved the target lesion primary patency end point at 6 months as compared to 0% of the control group (P = 0.015), but this did not translate into an improvement in secondary patency at either 6 or 12 months. Radiation therapy was found to be safe in the setting of hemodialysis vascular access dysfunction. Our results suggest that vascular brachytherapy is an intervention that is worthy of further examination in the setting of non-thrombosed dialysis access grafts.

Percutaneous Treatment of Dysfunctional Brescia-Cimino Fistulae Through a Radial Arterial Approach

BACKGROUND

Dysfunctional Brescia-Cimino fistulae contribute to significant morbidity in hemodialysis patients. These fistulae normally are treated through a retrograde venous approach. There are no data regarding a transradial approach. Furthermore, measurement of pressure reduction in the radial artery appears to be useful.

METHODS

We retrospectively examined 50 interventions to treat 49 patients (17 men, 32 women; mean age, 61.8 +/- 10.6 years) with Brescia-Cimino fistulae. Inclusion criteria were patients with palpable radial arteries and dysfunctional end-to-side Brescia-Cimino fistulae. Patients with infected fistulae, contrast allergy, upper-arm/synthetic graft/central-vein stenosis, and end-to-end Brescia-Cimino fistulae were excluded from the study. Radial arterial pressures before and after angioplasty were compared as a surrogate of stenosis relief. Anatomic and clinical success rates were calculated.

RESULTS

Sixty-five stenoses and 4 total occlusions were treated through radial access. All radial punctures were successful, except in 1 patient. Most lesions were located in the cephalic vein (87%). Mean length of treated lesions was 4.1 +/- 2.8 cm. Mean pretreatment diameter of lesion stenoses was 76.7% +/- 12.1%. Mean posttreatment diameter stenosis was 22.6% +/- 8.2% (P < 0.001). Systolic, diastolic, and mean blood pressures recorded from the radial artery decreased from 130 +/- 40, 60 +/- 18, and 87 +/- 27 to 88 +/- 40, 43 +/- 18, and 60 +/- 26 mm Hg (P < 0.001, P < 0.001, and P < 0.001), respectively. The anatomic success rate of the transradial approach was 91.3%. The clinical success rate of the transradial approach was 96%.

CONCLUSION

The transradial approach is a feasible and highly effective approach to treat dysfunctional Brescia-Cimino fistulae. Measuring blood pressure reduction through the radial artery appears promising as a hemodynamic evaluation method.

Hemodialysis vascular access dysfunction: a cellular and molecular viewpoint

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population. The major cause of hemodialysis vascular access dysfunction is venous stenosis as a result of neointimal hyperplasia. Despite the magnitude of the clinical problem, however, there has been a paucity of novel therapeutic interventions in this field. This is in marked contrast to a recent plethora of targeted interventions for the treatment of arterial neointimal hyperplasia after coronary angioplasty. The reasons for this are two-fold. First there has been a relative lack of cellular and molecular research that focuses on venous neointimal hyperplasia in the specific setting of hemodialysis vascular access. Second, there have been inadequate efforts by the nephrology community to translate the recent advances in molecular and interventional cardiology into therapies for hemodialysis vascular access. This review therefore (1) briefly examines the different forms of hemodialysis vascular access that are available, (2) describes the pathology and pathogenesis of hemodialysis vascular access dysfunction in both polytetrafluoroethylene grafts and native arteriovenous fistulae, (3) reviews recent concepts about the pathogenesis of vascular stenosis that could potentially be applied in the setting of hemodialysis vascular access dysfunction, (4) summarizes novel experimental and clinical therapies that could potentially be used in the setting of hemodialysis vascular access dysfunction, and, finally, (5) offers some broad guidelines for future innovative translational and clinical research in this area that hopefully will reduce the huge clinical morbidity and economic costs that are associated with this condition.

Does monthly native arteriovenous fistula blood-flow surveillance detect significant stenosis--a randomized controlled trial

BACKGROUND

Clinical practice guidelines recommend that the preferred method of surveillance for arteriovenous fistula (AVF) is the measurement of AVF blood flow (Qa). As these recommendations are based on observational studies, we conducted a randomized, prospective, double-blind, controlled trial to assess whether Qa surveillance results in an increased detection of AVF stenosis.

METHODS

A total of 137 patients were randomly assigned to receive either continuing AVF surveillance using current clinical criteria (control, usual treatment) or usual treatment plus AVF blood-flow surveillance by ultrasound dilution (Qa surveillance group). The primary outcome measure was the detection of a significant (>50%) AVF stenosis.

RESULTS

There were 67 and 68 patients assigned to the control and Qa surveillance groups, respectively. Patients in the Qa surveillance group were twice as likely to have a stenosis detected compared with the control hazard ratio (HR) confidence interval (CI) group (2.27, 95% 0.85-5.98, P = 0.09), with a trend for a significant stenosis to be detected earlier in the Qa surveillance group (P = 0.09, log rank test). However, using the Qa results alone prior to angiography, the area under the receiver operating characteristic curve demonstrated, at best, a moderate prediction of (>50%) AVF stenosis (0.78, 95% CI 0.63-0.94, P = 0.006).

CONCLUSION

This study demonstrates that the addition of AVF Qa monitoring to clinical screening for AVF stenosis resulted in a non-significant doubling in the detection of angiographically significant AVF stenosis. Further, large multi-centre randomized trials are feasible and will be necessary to confirm whether Qa surveillance and the correction of detected AVF stenosis will lead to a reduction in AVF thrombosis and increased AVF survival.

Maintenance and salvage of arteriovenous fistulas

PURPOSE

To describe the number and type of percutaneous interventions required to promote maturation and maintain patency of hemodialysis fistulas.

MATERIALS AND METHODS

One hundred fifty-four hemodialysis fistulas were created in 146 patients by a single surgeon between August 2001 and March 2005. There were 88 male patients (60%), and the median age of the group was 66 years. The records of all percutaneous procedures performed on these patients were retrospectively reviewed. The medical records from the hemodialysis treatment centers were also reviewed to assess fistula patency during the follow-up period.

RESULTS

Of the initial 154 fistulas created, 112 (73%) were successfully used for hemodialysis. One hundred thirteen procedures were performed to promote maturation of 65 fistulas (1.7 procedures per fistula), including 66 venous angioplasty procedures, 16 arterial angioplasty procedures, ligation of 21 venous side branches, five thrombectomy procedures, three banding procedures, and two other procedures. Only 48 of these nonmaturing fistulas (74%) became functional. Sixty-three mature fistulas required 209 procedures (3.3 procedures per fistula, 1.75 procedures per access-year) to maintain vascular access patency. These included 174 venous angioplasty procedures, 18 arterial angioplasty procedures, 14 thrombectomy procedures, ligation of three venous side branches, and two stent placement procedures. The mean follow-up period for all 154 fistulas was 317 days (range, 12-1,138 days). Primary patency rates at 90, 180, and 360 days were 71%, 69%, and 64%, respectively, and secondary patency rates were 73%, 72%, and 68%, respectively.

CONCLUSIONS

Percutaneous procedures can promote maturation and maintain patency of arteriovenous fistulas. However, despite numerous procedures to promote maturation, only 74% of nonmaturing fistulas became functional.

Percutaneous management of perianastomotic stenosis in arteriovenous fistulae: Results of a prospective study

Surgical creation of new anastomosis has been proposed as the preferred treatment for perianastomotic stenoses of fistulae. However, disadvantages of surgical approach have included (1) frequent conversion of fistula to a graft by using synthetic graft material to create a new anastomosis, (2) shortening the length of the cannulation segment by proximal autologous arteriovenous neoanastomosis, and (3) abandoning the fistula altogether in favor of a synthetic graft. We report the results of a prospective study using percutaneous balloon angioplasty (PTA) to treat fistulae with perianastomotic lesions. Seventy-three consecutive patients undergoing 112 PTA procedures for the treatment of perianastomotic lesions were studied. Primary and secondary patency rates were calculated. Procedure success, procedure-related complications, and conversion of fistulae to grafts were recorded. The initial success rate was 97%. The degree of stenosis before and after PTA was 81 +/- 9 and 11+/-11%, respectively. Primary patency rates at 6, 12, and 18 months were 75, 51, and 41%, respectively. Secondary patency rates at 6, 12, and 18 months were 94, 90, and 90%, respectively. Grade I hematoma occurred in three and vein rupture in two cases. No grafts were inserted. These outcomes are superior to those that have been reported for surgery. The outpatient PTA is safe and effective for the management of perianastomotic stenosis. Because of its advantage of fistula preservation, the percutaneous approach should be considered as the preferred first-line therapy for the management of perianastomotic fistula lesions.

Prospective Study of Balloon Inflation Pressures and Other Technical Aspects of Hemodialysis Access Angioplasty

PURPOSE

Balloon angioplasty is a mainstay in the treatment of failing or thrombosed hemodialysis access grafts and fistulas. A sizable body of outcomes data exists concerning percutaneous transluminal angioplasty (PTA) in hemodialysis access, yet there is a relative paucity of technical information available, especially regarding dilation pressures. The aim of the present study was to compile such information, which can be critical to the choice of devices for PTA and to the design of future clinical trials seeking to improve outcomes in this area.

MATERIALS AND METHODS

Technical data were collected prospectively for 102 PTA procedures (66 prophylactic PTA procedures and 36 PTA procedures performed during access thrombectomy). Demographic data concerning the access were collected. Technical data were collected individually for each lesion treated, including lesion location; degree of stenosis (in quartiles); lesion length; PTA balloon brand, size, and length; pressure at which the waist of the balloon was effaced; residual stenosis; and reason for additional balloons or inflations if used. Outcomes data other than residual stenosis were not collected, but the endpoint for all interventions was a thrill in the access.

RESULTS

A total of 230 lesions were treated. Two (1%) could not be successfully treated with PTA despite the use of "ultra high" pressure (approximately 40 atm); one was treated successfully with parallel wire technique and the other was revised surgically after the use of a cutting balloon also failed. Overall, 55% of lesions required pressures greater than 15 atm to efface the waist. Excluding initial failures, 20% of lesions in native fistulas and 9% in grafts required very high pressure (>20 atm) to efface the waist (P = .02). High pressure was needed less frequently in PTA procedures performed in the setting of thrombectomy procedures than in prophylactic PTA procedures (P = .0001). Residual stenosis was positively correlated with severity of initial stenosis and negatively correlated with duration of inflation.

CONCLUSIONS

Conventional angioplasty balloons are inadequate for the treatment of most hemodialysis access stenoses. High pressures (>15 atm) are commonly needed for PTA in hemodialysis access. Very high pressures (>20 atm) are more frequently needed in native fistulas.

Percutaneous declotting of virgin femoral hemodialysis grafts

OBJECTIVE

The objective of our study was to evaluate outcomes of percutaneous declotting procedures in patients with prosthetic femoral dialysis grafts.

MATERIALS AND METHODS

A retrospective review of all pharmacomechanical femoral dialysis graft declotting procedures performed in our hospital between May 11, 1993, and April 30, 2003, was performed. A total of 110 procedures were performed on 25 patients (nine males, 16 females; age range, 17-80 years; mean age, 49 years) with 30 grafts.

RESULTS

Technical success was 97.3%. Using life table analysis, 30-day postinterventional primary patency was 72%, 90-day primary patency was 46%, 180-day primary patency was 25%, and 365-day primary patency was 4%. The 30-day secondary postinterventional patency was 93%, 90-day secondary patency was 86%, 180-day secondary patency was 76%, and the 365-day secondary patency was 51%. An average of 1.96 declotting procedures were performed per year of dialysis.

CONCLUSION

Percutaneous declotting of femoral hemodialysis grafts has technical success and patency rates similar to those for percutaneous declotting in the upper extremities. Results of this series exceeded criteria established by the National Kidney Foundation in the "Dialysis Outcome Quality Initiative" for immediate patency and unassisted 3-month patency.

Tenecteplase in the Treatment of Thrombosed Hemodialysis Grafts

A pilot study was carried out to prospectively evaluate the efficacy and safety of Tenecteplase (TNKase) using a modified 'lyse and wait" technique with percutaneous transluminal angioplasty (PTA) to treat thrombosed hemodialysis arteriovenous grafts (AVG)s. Seven patients with eight hemodialysis AVGs were treated and followed up to 1 year. Dosing included 1 mg TNKase and 3,000-4,000 U of heparin. Technical and clinical success rates were 100% and 88%, respectively. No major complications occurred. Primary patency rates at 30, 90, and 180 days were 62%, 50%, and 33%, respectively. TNKase, used in this fashion, may be comparable to alteplase and reteplase for safe and effective thrombolysis of PTFE dialysis grafts.