A reliable vascular access is a key component of successfully treating end-stage renal disease. Surveillance of the access can identify luminal narrowing and provide sufficient lead time for intervention prior to thrombosis.1

Angioplasty has become the main therapy of choice to treat access dysfunction. Despite technical success in treating the luminal narrowing, the restenosis rate is very high. Only 40-50% of accesses maintain patency in the six months post-angioplasty without further procedures.2 Success of an angioplasty procedure is measured in terms of immediate radiological improvement in luminal diameter. A decrease to 30% or lower residual stenosis is considered “success.”3 Elastic recoil is common after an angioplasty which may or may not be apparent immediately.4

Assessment of the success of an angioplasty is not optimal due to lack of a standardized test or methodology. To address this need, researchers from Henry Ford Hospital in Detroit reported in a study presented at ASN Renal Week last November about using change in derived static venous pressure ratio as a predictive measure for access survival and the need for further intervention post-angioplasty.5

Surveillance and its impact

Surveillance methods based on either flow or pressure are available for monitoring vascular access in hemodialysis patients. Surveillance is traditionally used to identify an access with a significant stenosis which might cause clinical symptoms.

Hemodialysis patients affiliated with Henry Ford Health System /Greenfield Health System are monitored using the surveillance tool Vasc-Alert. During each dialysis session, the arterial and venous pressure recorded as part of the hemodialysis procedure is captured and used to calculate a venous access pressure ratio. An alert is issued when the ratio is over 0.55 for three consecutive dialysis sessions. Based on this, staff can refer patients for further evaluation, which might include invasive studies like angiography and/or angioplasty. If a stenosis producing >50% luminal narrowing by diameter (> 75% cross sectional) is noted on an angiogram, then angioplasty can be performed. This may decrease the pressure across the angioplasty site but may not be consistent after every intervention.

The aim of the reported study was to define the change in VA pressure ratio after angioplasty, and determine if this change can be predictive of access survival.

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Analysis was completed on 92 subjects [females 57%; black 88%; and diabetes mellitus 61%] including 46 patients with an arteriovenous fistula having 94 procedures and 46 patients having an arteriovenous graft with 86 procedures. Patients with a VAPR Delta < 0% had a two-fold increase in the likelihood of fistula failure, as compared to those with a VAPR Delta ≥ 0%, p = 0.003. Arteriovenous fistula with no VAPR decline (<0%) post-intervention when compared to AVF with any decline (> 0%) required more subsequent procedures (64% vs 47%) and with fewer days to next procedure (75 vs 149 d). Likelihood of graft failure in AVG patients with VAPR Delta <10% doubled, as compared to those with a VAPR Delta ≥10% (p = 0.010) and required more subsequent interventions and with fewer days to their next procedure.

Significance

Vascular accesses for dialysis experience frequent dysfunction due to intra-access stenosis from neo-intimal hyperplasia. Surveillance methods like the venous access pressure ratio test can be used to monitor and identify dysfunctional accesses and allow timely referral for evaluation and treatment to prevent future thrombosis. Anatomic factors related to access age, location, and extent of stenosis are known to be predictors of restenosis post angioplasty. Distal radial artery pressure gradient, trans-lesional pressure ratio, and catheter based flow studies are reported to predict interventional procedure’s technical and patency outcomes.However, a lack of standardization with limited usability and requirement of additional resources make them less applicable as a standard measure in clinical practice.

Researchers from Henry Ford Hospital report for the first time an automated vascular access pressure-based measure (Vasc-Alert), which can predict access survivability and necessity of further interventions. Identifying an inadequate access pressure response to an intervention may identify patients in need for further evaluation and treatment, probably reflecting on the quality and relative effectiveness of the procedures performed. The differing response noted in AVF and AVG suggests the notion that AVF and AVG may not respond similarly to an intervention.  This dissimilarity in response could be attributable to the ability of a fistula to soften pressure raised by its extendibility.

Conclusion

In the era of value based payment scenario, it is extremely important to identify measures to assess the quality of an intervention which are simple, readily available and can predate warning from traditional symptoms of access dysfunction. Early recognition of failing access, and/or a functional failure of an endovascular intervention would be an additional advantage. Hemodialysis access interventions have been increasing but objective measure to assess the quality of interventions are lacking. Parameters currently described in medical literature need specialized tests, add to the cost of intervention and are not standardized across differing practice patterns. Further studies are needed to standardize the use of a VAPR Delta into a routine procedure outcome measure.

References

  1. Besarab A, Sullivan KL, Ross RP, Moritz MJ. Utility of intra-access pressure monitoring in detecting and correcting venous outlet stenoses prior to thrombosis. Kid Int. 1995;47:1364-1373.
  2. Dember LM, Beck GJ, Allon M et al. Effect of clopidogrel on early failure of arteriovenous fistulas for hemodialysis: a randomized controlled trial. JAMA. 2008;299:2164-2171.
  3. Navuluri R, Regalado S. The KDOQI 2006 Vascular Access Update and Fistula First Program Synopsis. Semin Intervent Radiol. 2009;26:122-124.
  4. Rajan DK, Sidhu A, Noel-Lamy M et al. Elastic recoil after balloon angioplasty in hemodialysis accesses: Does it actually occur and is it clinically relevant? Radiology. 2016;279:961-967.
  5. Kumbar L, Zasuwa G, Besarab A, Hirschman K, Yee J. Post-endovascular intervention venous access pressure ratio (VAPR) predicts access