Medial cephalic to proximal ulnar artery fistulas enabled by a nitinol extravascular support device produce significantly higher maturation rates than brachial-based fistulas

Abstract

The proximal ulnar artery is rarely used for arteriovenous fistula creation. Here, an extravascular nitinol support device (VasQ, Laminate Technologies) was evaluated to facilitate maturation, confirmed by successful two-needle cannulation or observed on ultrasound imaging. Outcomes were compared with 158 unsupported brachial and 132 proximal radial artery fistulas by χ² test and logistic regression analysis. Proximal ulnar fistulas were created in 65 consecutive patients. The unassisted maturation rate was 77% (50/65), which was significantly higher in the ulnar artery group (P = .009). Externally supported proximal ulnar artery inflow may be the preferred alternative to unsupported brachial and proximal radial arteries for fistula creation.

Brachial artery-based fistulas (BAFs) tend to be the preferred upper arm access in the United States for their high maturation rates and a relatively superficial conduit, for easier cannulation. However, brachial artery inflow carries the highest risk of steal, aneurysmal formation, cephalic arch stenosis, and compromised cardiac function.1, 2, 3, 4 As an alternative, surgeons have explored the proximal radial artery fistula (proxRAF) as the inflow to leverage the smaller diameter and split flow with the ulnar artery to avoid these high-flow complications.5, 6, 7, 8, 9, 10, 11 The reported outcomes from proxRAFs were promising, but when compared directly with BAFs, the maturation rates were significantly lower.¹² For this reason, BAF remains the primary option for an upper arm fistula at most access centers despite the higher risk of complications.

The proximal ulnar artery fistula (proxUAF), with a diameter and volume flow consistently between the brachial and radial artery diameters, is a rarely explored inflow option that could strike the right balance between high maturation rates with a low risk of high-flow complications. Endovascular fistula studies using the ulnar artery report low incidences of steal and aneurysm formation.13, 14, 15 A description of surgically created proxUAF reports a low incidence of steal, but has been limited to highly selected patients with no other inflow options and using the brachial vein as the outflow.^10,11 Concerns about compromising the dominant distal perfusing artery as well as external compression of the juxta-anastomotic region (JAR) by the surrounding muscles (pronator teres, biceps brachii, and brachialis) have rendered the proxUAF largely unexplored as a viable access option.

Here, the proxUAF was explored as the primary upper arm inflow using a nitinol-based extravascular support device to reinforce the JAR against external compression in patients with an intact palmar arch, detected preoperatively using the modified Allen's test. The rationale for using the device in this location is based on its nitinol construction, consisting of a rigid brace woven into a funnel configuration (Fig 1,A). The brace is positioned around the anastomosis, protecting it from external compression, sets at a 50° angle, and ends as a rigid ring, which inhibits overdilation of the immediate postanastomotic vein (Fig 1,B). The flexible braid continues from the ring at the set angle and gradually increases in diameter by 50% over 2.3 cm to create a funnel, as opposed to the randomly ballooning segments of an unsupported anastomosis; this configuration leads to a less turbulent blood flow pattern and results in early transition to a laminar flow. Fig 2 presents a comparison of Doppler ultrasound evaluation images from a control group with unsupported proxRAFs (Fig 2,A) and from a group with externally supported (ES)-proxUAFs (Fig 2,B). Gradually increasing the vein diameter of the latter configuration is distinctly different from the irregularly changing diameters of the unsupported fistula. The use of this extravascular support device has demonstrated increased functional maturation in multiple studies worldwide for patients with RAF and BAF. However, its application to a proxUAF has not been reported previosuly.16, 17, 18, 19, 20, 21, 22, 23, 24, 25 Longer-term experience in endovascular fistulas with proxUAFs has demonstrated that if, at minimum, the palmar arch is intact, ulnar dominance would not result in compromised distal perfusion to the hand if selected as the inflow artery.^14,15

Fig 1.

(A) The VasQ external support nitinol device (Laminate Technologies). (B) Schematic representation of proximal ulnar externally supported (ES) arteriovenous fistula (AVF) creation through a perpendicular incision over the brachial artery bifurcation.

Fig 2.

Doppler ultrasound imaging of a proximal radial unsupported AVF from the control group (A) and an ES proximal ulnar arteriovenous fistula (B). External support device (VasQ, Laminate Technologies) (C). AVF, Arteriovenous fistula; ES, externally supported.

Methods

This external support device (VasQ, Laminate Technologies) is approved for clinical use in the United States by the Food and Drug Administration. The present report was not part of a clinical trial. The data were collected retrospectively from patient charts. Collection of information for the control group was completed after approval by the Catholic System Institutional Review Board committee. Retrospective collection of the ES-prUAF cohort was approved by the University of Buffalo Institutional Review Board. In both cases, informed consent was waived due to the use of deidentified data

According to a previously published protocol,^12,26 all patients were evaluated by Doppler ultrasound examination on the day of fistula creation for selection of an inflow artery and an outflow vein. Both the control and ES-prUAF groups included consecutive patients following the same clinical practice protocol, with a goal of the creation of an arteriovenous fistula (AVF) at the most distal site, with a combination of a vein diameter of >2.5 mm with a compressible, patent vein and an arterial flow volume of >20 mL/min. Vein wall thickening and arterial morphology (calcifications and atherosclerosis) were not considered within the decision-making process of this protocol. The modified Allen's test was performed by means of a portable pulse oximeter in the ES-prUAF and digital plethysmography in the control group. Recovery of digital perfusion to baseline within a few seconds after flat line observed during compression of both the distal radial and distal ulnar arteries and release of the artery under examination determined patency of the palmar arch and a low risk for the development of steal syndrome. In cases with a lack of perfusion recovery during compression of one artery and only at the level of the wrist, this artery was not used as the inflow artery, as the finding was considered high risk for the development of steal syndrome. In these cases, proximalization of the arterial anastomosis procedure with a polytetrafluoroethylene graft was preferred. No other inclusion or exclusion criteria for any for the groups were applied.

ES-proxUAFs were created in all patients who met these criteria for the ulnar artery and medial cephalic vein. In the control group, ulnar inflow was rarely considered, due to anatomical difficulties encountered with this fistula configuration, because the ES device was not available at the time. When the ulnar artery was used, the patient had an early brachial artery bifurcation (except in one case with conventional anatomy) and the anastomosis constructed was side to side. The ES device has also been used for a small number of other fistula creation configurations during the study period; therefore, these cases are not reported herein. All procedures were performed by a single surgeon, under local anesthesia with sedation.

Intravenous antibiotics (cephalosporin or vancomycin in allergic patients) were administered in all cases before skin incision. Anticoagulants were not administered.

The procedure began with a transverse incision three fingerbreadths from the elbow crease. The medial cephalic vein was identified and mobilized (Fig 3,A). The vein was dissected and the distal segment ligated and transected, leaving a length of approximately 3 to 4 cm distal to the basilic to cephalic confluence. When the perforating vein was encountered joining the median cephalic vein, usually at the most proximal end of the medial cephalic vein, it was ligated and transected (Fig 3,B). At this point, a functional test was performed by inserting vein dilators up to 3 mm within the vein and evaluating resistance. If resistance was encountered, the area of stenosis was evaluated by ultrasound examination, but if dilatation up to 3 mm even by carefully forcing the vein dilators could be accomplished, the vein was used. If the vein was occluded and the occlusion could not be crossed, an alternative fistula or graft configuration was considered, depending on the level of venous obstruction. The medial cephalic vein was then gently dilated with saline and its diameter was measured, using the disposable model selection tool provided with the VasQ Extravascular Support device (Laminate Technologies) (Fig 3,C). In the control group, gentle saline dilatation of the vein was not performed, because there was no need for ES device sizing. The ulnar artery was then accessed by incising the fascia and retracting the pronator teres, freeing enough tissue around the artery to accommodate the extravascular support device (Fig 3,D). Partial transection of the muscle was not considered or performed, because the extravascular support alone was determined to be sufficient to counteract the compressive force. Approximately 1.0 to 1.5 cm of the artery distal to the brachial artery bifurcation was exposed and controlled with vessel loops (Fig 3,D). The artery was measured using a disposable model selection tool. The VasQ extravascular support device was selected as the larger of the two model sizes from either the venous or arterial measurements and slid around the vein via forceps. The device was tucked under the skin flap to allow for unencumbered creation of a standard end-to-side anastomosis with a 6-mm anastomosis, placed just distal to the brachial to ulnar bifurcation. Once hemostasis was confirmed, the vein was depressurized to allow the device to slide down onto the anastomosis. The device eyelets were secured together around the artery with a 7-0 Prolene suture (Ethicon) and blood flow was restored to the vein to complete the procedure (Figs 3E, F).

Fig 3.

Stages of anatomical dissection and creation of the ES proximal ulnar artery AVF. Medial cephalic dissection, transection and inflation with saline for device sizing and evaluation of vein wall compliance (A-C). Ulnar artery dissection and exposure of 1.0 to 1.5 cm after the bifurcation with a 6.0-mm arteriotomy (D). Completion of the ES anastomosis (E). Release of pronator teres retraction (F). AVF, Arteriovenous fistula; ES, externally supported; ES-proxUAF, externally supported proximal ulnar artery fistula.

Patients in both groups were then followed at 2 weeks to assess the surgical wound and flow via a physical and Doppler ultrasound examinations. Assessment for eligibility for cannulation was performed at 4 weeks, with maturation procedures scheduled within 1 week, if not on the same day, as described in the previously published protocol for this center.²⁶ An AVF was considered mature either when it was successfully used for dialysis or a Doppler ultrasound examination was found in the chart, documenting maturity by the National Kidney Foundation Kidney Disease Outcome Quality Initiative guidelines criteria, for patients on predialysis with chronic kidney disease and patients who expired before cannulation of the fistula or confirmed use for dialysis for end-stage kidney disease (ESKD).²⁷ Physiological maturation was defined as an arterial volume flow of 600 mL/min and a 6-mm vein diameter at the cannulation zone. Confirmed use of the AVF was based on patients receiving adequate dialysis via two-needle cannulation in at least one session.

Primary maturation was defined as successful maturation without a procedure other than the initial creation, except for second-stage vein elevations, predicted preoperatively by Doppler ultrasound examination, based on the quality of the upper arm cephalic vein. Small or occluded cephalic veins would result in basilic vein outflow from the ES-proxUAF, requiring a second stage vein elevation procedure. Vein elevations were performed via two or three transverse incisions for mobilization of the vein, placement to a more superficial position, and approximation of the fascia under the vein, without the need to create a new anastomosis. The same procedure was followed for cephalic veins deeper than 1.0 to 1.5 cm. Elevations were performed on mature, by physiological criteria, veins after the 4-week postoperative evaluation. Secondary maturation was defined as maturation accomplished after at least one additional procedure other than elevation.

Outcomes for ES-proxUAFs were compared with 158 BAF and 132 proxRAF historical controls from a previously published database collected at the same center for fistula creations performed by the same surgeon.¹² Statistical analysis was performed using the χ² test and independently compared the ES-proxUAF with BAF and proxRAF historical outcomes. Categorical variables were compared using Fisher's exact test, and relative risks (RRs) with 95% confidence intervals (CIs) were calculated. A multivariate logistic regression analysis was used to determine statistical difference in primary maturation for ES-proxUAF, BAF, and proxRAF. Factors included in the multivariate assessment were AVF location, sex, age >70 years, race, diabetes, body mass index of >30, ESKD, and preoperative vessel diameter. Kaplan-Meir survival analysis was not performed, due to lack of timepoint reports in the control group data.

Results

ES-proxUAFs were created in 66 patients eligible for upper arm fistulas from March 2024 to August 2025. One patient from the ES-proxUAF group expired and was excluded from the analysis. The mean follow-up period was 50 ± 38 days. Control group data were collected from consecutive patients who had an AVF created between October 2013 and November 2017. An external support device was not commercially available during that time. The mean follow-up was 56 ± 77 days (P = .44). Patients with unknown outcomes were excluded from both groups. No other exclusion criteria were applied. The mean vein diameter for the ES-proxUAF was 4.3 ± 0.8 mm. The only available information from the control group was that the vein diameter was always ≥2.5 mm. Demographics are listed in Table I.

Table I.

Demographics

	ES-prox UAF (n = 65)	BAF (n = 158)	Prox RAF (n = 132)
Male sex	45.5%	57.7%	51.10%
Race
White	71.2%	79.8%	75.50%
Black	16.7%	16.7%	18.00%
Age, years, median	71	69	68
BMI, median	28	26.5	29.5
ESKD	42.4%	71.4%	73.40%
Diabetes	59.1%	58.9%	68.30%
Hypertension	93.9%	98.2%	100%
Artery diameter, mm, mean	4.3	5.1	3.8

BMI, Body mass index; BUF, brachial artery based arteriovenous fistula; ESKD, end-stage kidney disease; ES-proxUAF, externally supported proximal ulnar arteriovenous fistula; proxRAF, proximal radial artery based arteriovenous fistula.

In the ES-proxUAF group, no complications were observed over the follow-up period. No infections due to the presence of the extravascular support device and no evidence of steal were observed. In the BAF control group, 0.6% of patients (1/158) had an infection and there was a 3.2% incidence (5/158) of steal syndrome (P = .17). No patient from the prRAF group developed steal syndrome or an infection. Immediate fistula thrombotic episodes diagnosed within 2 weeks from fistula creation were observed in 10.8% of patients (7/65) in the ES-prUAF group. In the control group, the 2-week thrombosis rate was 12.0% (19/158) for the BAF (P = .78) and 8.3% (11/132) in the prRAF (P = .22) groups. Only one patient from the prUAF group underwent early postoperative surgical revision (1.5%) compared with 5.7% (9/158) (P = .28; RR, 0.27) in the BAF group and 16.0% (21/132) on the prRAF group (P = .003; RR, 0.1; 95% CI, 0.01-0.70).

Primary maturation was observed in 76.9% of patients with an ES-proxUAF (50/65). By comparison, primary maturation rates for patients with an ES-proxUAF were significantly higher by χ² test at 76.9% than the historic controls of BAF and proxRAF at 58.8% (93/158; χ² = 4.1; P = .04) and 49.6% (65/131; χ² = 13.3; P = .0003), respectively (Fig 4). In the multivariate analysis, ES-proxUAF was still a statistically significant factor in achieving primary maturation (P = .009). All other factors such as sex, race, ESKD, diabetes, age, and body mass index were not significantly associated with primary maturation (Table II).

Fig 4.

Primary and secondary maturation rates. The P values represent a comparison of primary maturation rates with the ES-proxUAF. BAF, Unsupported brachial artery-based fistulas; ES-proxUAF, externally supported proximal ulnar artery fistulas; Primary maturation, mature fistula without additional procedures; proxRAF, unsupported proximal radial artery-based fistulas; Secondary maturation, mature fistula after additional procedures.

Table II.

Primary maturation logistic regression analysis

Factor	HR [95% CI]	P value
AVF type vs ES-proxUAF
ProxRAF	0.22 [0.11-0.45]	.001
BAF	0.4 [0.20-0.81]	.010
Demographics/comorbidities
Male sex	1.28 [0.80-2.05]	.312
Race: Black	0.8 [0.44-1.43]	.448
Diabetic	1.1 [0.68-1.77]	.703
ESKD	0.71 [0.43-1.16]	.169
Arterial diametera	4.53 [0.55-37.46]	.162
Obese	0.89 [0.55-1.43]	.628
Elderly	0.8 [0.51-1.25]	.326

AVF, Arteriovenous fistula; BAF, brachial artery based arteriovenous fistulas; CI, confidence interval; ES-proxUAF, externally supported proximal ulnar arteriovenous fistula; ESKD, end-stage kidney disease; HR, hazard ratio; proxRAF, unsupported proximal radial artery-based arteriovenous fistulas.

Boldface entries indicate statistical significance.

Obese was defined as having a body mass index of >30.

Elderly was defined as age >70 years.

^aPer 1-mm increase.

At the end of the follow-up period, 20 fistulas were used for dialysis, 4 patients with physiologically matured fistulas refused cannulation, 1 patient expired before cannulation, and another 25 patients with physiological maturation are still in a predialysis state or underwent transplantation. Secondary maturation was achieved in another 9% (6/65), by percutaneous transluminal angioplasty of a distal arm cephalic vein in five cases (7.7%) and percutaneous transluminal angioplasty of central veins in one (1.5%). Four patients (6%) had a history of a previous AVF or arteriovenous graft on the same or contralateral arm. The number of previous access procedures was not investigated in the control group. Logistic regression analysis on the need for a maturation intervention showed significantly higher chances on BAFs and prRAFs (odds ratio, 2.19 [95% CI, 1.03-4.65; P = .04] and odds ratio, 3.71 [95% CI, 1.76-7.79; P = .001]) compared with proxUAFs (Table II). A detailed analysis of maturation procedures per patient is provided in Table III.

Table III.

Maturation procedures per patient

	ES-proxUAF per patient	BAF per patient (P value)	proxRAF per patient (P value)
Maturation procedures	0.23	0.45 (.042)	0.75 (.001)
PTA	0.14	0.21 (.21)	0.35 (.053)
Revision	0.03	0.14 (.04)	0.31 (.001)
Thrombectomy	0.06	0.08 (.53)	0.05 (.78)

BAF, Unsupported brachial artery-based fistulas; ES-proxUAF, externally supported ulnar fistulas; proxRAF, unsupported proximal radial fistulas; PTA: percutaneous transluminal angioplasty.

Boldface entries indicate statistical significance.

Statistical analysis was performed as a logistic regression using ES-proxUAF as the reference.

Five unsupported ulnar-based fistulas were identified in the control group; 80% (4/5) were constructed in patients with early brachial artery bifurcation and 20% (1/5) on a patient with conventional anatomy. They were all side-to-side anastomotic configurations and 40% (2/5) achieved primary maturation on the first category; the others failed immediately without further interventions performed, due to challenging anatomy. Therefore, among ulnar fistulas, 76.9% of ES-proxUAFs reached primary maturation compared with 40% side-to-side unsupported ulnar fistulas. Although maturation was more common in the ES-proxUAF group by Fischer's exact test (odds ratio, 5.0), the difference did not attain statistical significance (P = .11), likely due to the small sample size of the side-to-side group.

Observations made via Doppler ultrasound assessment of both the control and ES-prUAF groups suggest that extravascular support resulted in an earlier transition to a laminar-like low profile and prevented changes to the anastomotic configuration as compared with AVFs without extravascular support (Fig 2). The extravascular support device creates a diametrically tapered transition of flow outward in the JAR as opposed to irregular diametric expansion.

Discussion

The proximal ulnar artery presents consistent anatomical orientation, location, and diameter, making this operation predictable and reproducible, especially in conjunction with an extravascular support device. As described by Al Talalwah and Getachew,²⁸ the proximal segment of the ulnar artery is located distal to the antecubital fossa between the brachial artery confluence and the interosseous branch. The segment descends downward at an angle of 8° to 30° for a length of 19.5 to 19.9 mm long with a consistent diameter of ∼4 mm. Exposing the artery requires dissection through multiple tissue layers and retracting of the pronator teres, which would likely result in some degree of compression of any venous outflow that was mobilized to this position. For this reason, the extravascular support device was used to protect and maintain the desired anastomotic configuration. The preset angle of the extravascular support device was ideal for the natural approach of the median cephalic vein turndown to the ulnar artery.

The selection of the medial cephalic vein at the proximal forearm for the anastomosis provided a straight-line outflow to the upper arm cephalic, as well as leaving the basilic vein as a secondary option without the need for flow diversion procedures. The medial cephalic vein is underused in access creation; surgeons typically select either the cephalic vein proximal to the basilic bifurcation or the perforating vein for an AVF in the proximal forearm.5, 6, 7, 8, 9 The median cubital vein has sufficient length and no side branches to manage, unlike the perforating vein, which tends to be shorter with multiple side branches. Additionally, the perforating vein tends to create a split flow AVF, which has demonstrated to not provide sufficient flow to a target cannulation zone without additional flow diversion procedures to meet the pump speed demands in the United States.^29,30 However, the more distal location on the ulnar artery required to use the median cubital vein leaves the JAR at risk for external compression from the pronator teres muscle in the proximal forearm. For that reason, extravascular support is required to protect the JAR and facilitate functional maturation via the medial cephalic, as was used in this study. No flow diversion procedures were required for the ES-proxUAF in this study; sufficient outflow through the upper arm cephalic vein to support cannulation occurred in most patients. Basilic vein dominance occurred only in cases where the cephalic vein was not anatomically suitable for fistula creation and could be predicted via preoperative ultrasound examination. The predictability of basilic dominant flow allows patients to consent to the procedure with am understanding of the likelihood of a second stage elevation procedure being required. The more distal location of the anastomosis enabled the basilic vein to be elevated using three transverse incisions without the need for disconnecting, tunnelling, and reanastomosing the outflow. This procedure was successful in all basilic vein elevation cases, without the need for conversion to transposition with a new anastomosis. A technical consideration in this scenario is for careful mobilization of the nerves and occasional separation of small sensory nerve bundles from the main nerve to the direction of their fibers, without causing nerve injury. This maneuver allows positioning of the nerve bundles to the sides of the basilic vein, permitting nerve crossover only at desirable areas, without tension. The technique can be used in difficult cases, when the nerves are wrapped around the vein, which can cause occasional self-limiting forearm skin paresthesia. The use of the medial cephalic vein for outflow enables the ES-proxUAF to effectively replace the brachial artery as the primary inflow for both cephalic and basilic upper arm AVFs.

ES-proxUAF hemodynamics present as less turbulent than standard fistulas both in feel and in appearance under color Doppler ultrasound examination, which may account for the higher maturation rates. The extravascular support device is designed with a fixed 50° anastomotic angle and a 50% tapered increase in diameter to the outflow based on computational fluid dynamics modeling with an intent to reduce turbulence in fistula hemodynamics.²⁸ The impact of this design on patients has been found to promote a more stable, laminar-like flow profile as observed on magnetic resonance imaging and ultrasound flow vector studies.^31,32 The importance of a more stable, laminar-like flow in AVFs has been well described in the literature as a mitigating factor in the development of JAR negative remodeling that leads to failures.33, 34, 35, 36 A magnetic resonance imaging-based longitudinal imaging study by Remuzzi et al³⁷ highlighted the importance of retaining an optimal configuration during the maturation process. In that study, fistulas without extravascular support reported changes in structural configurations over the first year that had a significant impact on hemodynamics and functionality, whereas the extravascular supported fistulas retained the configuration created by the surgeon. Changes in structural configurations can be observed via ultrasound examination after creation if extravascular support is not used (Fig 2,A, vs Fig 2,B). The proposed mechanism of action for extravascular support may explain the low rate of JAR stenosis and subsequent significantly higher primary maturation rate reported here. To put the secondary maturation rate in context, defined as the need for maturation procedures, the Hemodialysis Fistula Maturation (HFM) study reported a 33% stenosis rate in the upper arm, with 42% in the JAR,³⁷ which correlated with a secondary maturation rate, as defined in here, of 49.9%.³⁸ Patients with an ES-proxUAF experience a higher primary maturation rates and a lower need for secondary maturation procedures than historical controls reported here or elsewhere in the United States.

Careful patient selection also likely contributed to the overall high primary maturation rate in addition to the clinical effect of the extravascular support. This center previously reported a significant improvement in overall primary maturation from 42% to 67% (P = .007) when only patients with a minimum arterial flow of >20 mL/min were selected for fistula creation, which was the standard protocol for the historic controls in this study.¹² Additionally, some patients who presented with early thrombosis failed the intraoperative functional test, in both groups, because they likely had a highly organized collagen reinforcement from prior vessel trauma, likely from an intravenous needle puncture. Pre-existing severe venous disease with >80% lumen reduction and significant aggregates of organized collagen, the strongest fiber within the extracellular matrix, have been reported to occur in 9.6% of patients.³⁹ A similar frequency of patients failed the intraoperative functional test here, which suggests an inability of the vein to distend in response to insertion of vein dilators or hydrostatic pressure and may be associated with increased venous stiffness from organized collagen in response to previous vessel trauma.40, 41, 42 Warning signs of a thickened vein wall may be observed via ultrasound examination, but the lack of distensibility must be confirmed with a functional test intraoperatively, because vein wall thickening may be due to vasospasm during the ultrasound examination. If the vein will not dilate, the likelihood of maturation failure is high. Unfortunately, the chronic nature of these severely diseased veins does not lend itself to successful interventions or revisions to mature the outflow. The best course of action when observed intraoperatively would be to convert the operative plan to an anastomosis to a more proximal artery or above the elbow with a healthy vein or a graft. This conclusion has changed our center's clinical protocol to rejecting every vein that fails functional testing. If this principle had been followed in the reported cases, a higher maturation rate could possibly have been achieved. Although the etiology of early AVF failure is multifactorial, further investigations of potential strategies to overcome this barrier are certainly warranted.

Delays in fistula primary maturation tend to be associated with the need to schedule and perform maturation procedures on AVFs with failure to mature. Additionally, surgical fatigue has been associated with decreased patient compliance and election to abandon their AVF for permanent central venous catheters (CVCs).⁴³ Strategies to improve primary maturation rates and decrease the need for additional procedures, such as the one described herein, can lead to a decrease in CVC rates. Previously, ES-AVFs have reported earlier times to primary maturation as compared with controls due to a decrease in the need for adjunct maturation procedures.17, 18, 19, 20, 21 However, this center, before the adoption of the ES-proxUAF, developed and applied a rapid maturation protocol, where maturation procedures were performed within 1 week of their first follow-up as necessary, and resulted in a significant decrease in time to functional maturation and CVC removal.²⁶ Even if implementation of such a protocol can be achieved, higher rates of primary maturation accomplished by the ES-proxUAF provide a significant patient benefit by avoiding additional procedures. The hemodynamics of this particular AVF configuration facilitated by the extravascular support as described likely influenced the observed increase in unassisted maturation of the vein. Of note is that, herein, the comparison is limited to being between ES ulnar artery and unsupported brachial and radial artery-based fistulas. The existing literature supports improvement in maturation rates of ES radial and brachiocephalic fistulas.17, 18, 19, 20, 21, 22, 23, 24, 25^,44,⁴⁵ Therefore, future direct comparisons of the ES-proxUAF rates with ES-proxRAF and ES-BAF maturation rates is warrantied. Such evaluations can possibly determine whether the difference observed here can be improved by the external support device only or that the proximal ulnar artery inflow remains an independently significant factor.

Limitations

This study was limited by the retrospective nature of data collection, lack of randomization, and short follow-up period. Although a prospective, randomized controlled study would be ideal, the consecutive nature of our patient inclusion strategy provided a real-world perspective that often is clouded by the stringent patient selection criteria of prospective studies. The comparative data in this study could suffer from a historical bias based on improved operator skill or advances in ultrasound imaging over the years that should be taken into consideration when interpreting the results. Finally, this initial study lacks multiyear follow-up to confirm both long-term patency and mitigation of high-flow complication risks when using the ulnar artery as a primary inflow with extravascular support. An additional follow-up analysis should be performed to confirm the long-term benefits of ES-proxUAFs.

Conclusions

This study demonstrated that the ES-ProxUAF may be a preferred alternative to either the BAFs or the ProxRAF to achieve higher rates of primary maturation and lower rates of additional procedures after AVF creation. Longer-term follow-up should be performed to confirm whether the ES-proxUAF will mitigate the risk of high-flow complications, such as steal and aneurysm formation.

Funding

Financial support for data collection was provided by Laminate Medical Technologies, Ltd.

Disclosures

G.B, is consultant for Laminate Medical Technologies, Ltd.

From the Society for Clinical Vascular Surgery