Development and validation of a risk score to prioritize patients for evaluation of access stenosis

Background

Access flow dysfunction, often associated with stenosis, is a common problem in hemodialysis access and may result in progression to thrombosis. Timely identification of accesses in need of evaluation is critical to preserving a functioning access. We hypothesized that a risk score using measurements obtained from the Vasc‐Alert surveillance device could be used to predict subsequent interventions.

Methods

Measurement of five factors over the preceding 28 days from 1.46 million hemodialysis treatments (6163 patients) were used to develop a score associated with interventions over the subsequent 60 days. The score was validated in a separate dataset of 298,620 treatments (2641 patients).

Results

Interventions in arteriovenous fistulae (AVF; n = 4125) were much more common in those with the highest score (36.2%) than in those with the lowest score (11.0). The score also was strongly associated with interventions in patients with an arteriovenous graft (AVG; n = 2,038; 43.2% vs. 21.1%). There was excellent agreement in the Validation datasets for AVF (OR = 2.67 comparing the highest to lowest score) and good agreement for AVG (OR = 1.92).

Conclusions

This simple risk score based on surveillance data may be useful for prioritizing patients for physical examination and potentially early referral for intervention.

Comparison of ultrasound scan blood flow measurement versus other forms of surveillance in the thrombosis rate of hemodialysis access: A systemic review and meta-analysis

BACKGROUND

The benefit of access flow surveillance in preventing vascular access thrombosis and failure remains controversial, as many randomized clinical trials (RCTs) have failed to demonstrate consistent results. The aim of this study was to perform a meta-analysis including newly published RCTs with a subgroup analysis for arteriovenous fistulas (AVFs) and arteriovenous grafts (AVGs).

METHODS

A systematic review of the available literature was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. An electronic search was conducted using the MEDLINE, EMBASE, and Cochrane Library databases of RCTs conducted from 1970 to 2017 that involved access flow surveillance. As a result, 9 RCTs met our criteria. The control group was defined by indirect and various surveillance methods such as dynamic venous pressure measurement and physical examination. Conversely, the interventional group was defined as a noninvasive duplex ultrasound scan (USS) or ultrasound dilution that directly measured the flow of vascular access.

RESULTS

The studies included 990 patients comprising 658 native AVFs and 332 AVGs. The prevalence of diabetes was 29.3%and 30.5% in the interventional and control groups, respectively. The estimated overall pooled risk ratio (RR) of thrombosis was 0.782 [95% confidence interval (95% CI), 0.553-1.107; P = .17], favoring interventional group, although this was not statistically significant. In the subgroup analysis, the pooled RR of thrombosis was .562 (95% CI, 0.346-0.915; P = .02) for AVFs, which significantly favored the interventional group. Conversely, the pooled RR for AVGs was 1.104 (95% CI, 0.672-1.816; P = .70).

CONCLUSION

The surveillance method to measure access flow through USS showed a significant benefit for reducing thrombosis in AVFs. The result encourages adherence to the current guidelines for AVFs. However, no benefit was found regarding AVGs. Recent guidelines with a "one-size-fits-all" approach may be revised to a "tailored-to-risk" approach.

Applicability of an entry flow model of the brachial artery for flow models of the hemodialysis fistula

The native arteriovenous fistula creates a shunt that provides the high blood flow that is needed for dialysis. Lumped parameter hemodynamic models of the arteriovenous fistula can be used to predict shear stresses and pressure losses and can be applied to help understand unsolved problems such as the high rate of arteriovenous fistula maturation failure. These models combine together flow components, such as arteries, stenosis, anastomoses, arterial compliance, and blood inertia, and each component must be modeled with an appropriate pressure-flow relationship. Poiseuille flow is generally assumed for straight vessels, but the unique high flow rates within the brachial artery of an arteriovenous fistula are expected to induce entry flow effects that are neglected in this model. To estimate the importance of these effects, brachial artery flow was modeled in a low-resistance network, such as the one that occurs when an arteriovenous fistula is constructed, through the lumped parameter model, and the predicted flow rates and pressures were compared to those predicted by computational fluid dynamics. When Poiseuille flow was assumed, the flow rate from the lumped parameter model was consistently larger than that from computational fluid dynamics, with a cycle-averaged error of 36.8%. When an entry flow model (Shah) was assumed, the lumped parameter-based flow was 6% lower than the computational fluid dynamics model at the peak of the flow waveform, and the cycle-averaged error was reduced to 7.8%. Thus, in a low-resistance (high flow) arteriovenous fistula circuit, an entry flow model can account for steeper near-wall velocity gradients. This result can provide a useful guide for designing engineering models of the arteriovenous fistula.

Monitoring and Surveillance of Hemodialysis Vascular Access Using StenTec and Physical Exam

Hemodialysis vascular access surveillance for hemodynamically significant stenosis can be a challenge because no universal gold standard exists. The StenTec Gauge measures static intra-access peak pressure and graphically displays the ratio of this pressure to systemic systolic (peak) arterial pressure (PIA ratio). In combination with careful physical exam (PE), the StenTec Gauge is an acceptable and cost-effective way of detecting hemodynamically significant stenosis in arteriovenous fistulas (AVF) or grafts (AVG). In a selected population of 21 hemodialysis patients with mature arteriovenous access, a StenTec reading and physical examination was measured on a weekly basis. Interventional procedures for suspected access dysfunction were performed if there was a greater than 25% increase of the PIA ratio from baseline in two consecutive readings, along with correlating clinical suspicion from physical examination findings. StenTec independently had a sensitivity of 56% and a specificity of 99% in detecting clinically significant stenosis. PE alone had a sensitivity of 89% and a specificity of 100%. StenTec combined with PE had a sensitivity of 100% and a specificity of 99% for predicting hemodynamically significant stenosis. StenTec detected 4 of 10 patients who had a PIA ratio value of ≥0.5, which correlates with current National Kidney Foundation Disease Outcomes Quality Initiative (KDOQI) criteria for mean intra-access pressure ratios indicating a clinically significant outflow stenosis. PE predicted 9 of 10 patients with stenosis, and the combination of StenTec and PE predicted all 10 patients with clinically significant stenosis using the KDOQI criteria for PIA ratio. Hemodynamically significant access stenosis can be detected with excellent accuracy using both StenTec and PE measurements combined for monitoring and surveillance methods.

Translesional pressure ratio predicts technical outcome and patency in angioplasty on outflow stenosis of hemodialysis graft

PURPOSE

Translesional pressure ratio (TLPR) indicating fractional flow reserve has been applied to physiological assessment of moderate coronary stenosis. The role of TLPR in hemodialysis (HD) patients with arteriovenous graft (AVG) outflow stenosis undergoing percutaneous transluminal angioplasty (PTA) is unclear. The purpose of the study was to assess the validation of TLPR in such patients undergoing PTA.

METHODS

Patients with pure AVG outflow stenosis confirmed by angiography were prospectively enrolled. A TLPR defined as a ratio of the mean pressure downstream to the lesion(s) to the vein-sided intragraft pressure was measured using a catheter pullback method. Relationship among TLPR, angiographic result and clinical outcome within 6 months was detected.

RESULTS

Of 65 PTAs, the post-PTA TLPR significantly increased (from 0.28±0.10 to 0.50±0.11; p<0.0001). A significantly greater pre-PTA TLPR was observed in the simple lesions at baseline compared with the complex lesions (0.32±0.09 vs. 0.20±0.06; p<0.0001). Post-PTA TLPR ≥0.5 was powerfully related to angiographic success (p<0.0001). The group with angiographic success plus post-PTA TLPR ≥0.5 had a longer PTA-free patency (208.7±188.7 vs. 109.8±67.7 days; p=0.013) compared with that with angiographic nonsuccess plus post-PTA TLPR <0.5.

CONCLUSIONS

Our data show that TLPR correlates well with lesion properties and angiographic results, and helps predict following unassisted patency. The study suggests TLPR as a hemodynamic indicator during PTA.

Vascular access surveillance: an ongoing controversy

Hemodialysis vascular access surveillance continues to be widely recommended despite ongoing controversy as to its benefit in prolonging access patency compared with clinical monitoring alone. The most common screening tests are access blood flow and dialysis venous pressure measurements. When surveillance test results cross a predetermined threshold, accesses are referred for intervention with correction of stenosis to reduce future thrombosis and prolong access survival. Current surveillance strategies have four components: (1) underlying condition; (2) screening test; (3) intervention; and (4) outcomes. However, limitations exist within each component that may prevent achieving the desired outcomes. This review discusses these limitations and their consequences. To date, randomized controlled trials have not consistently shown that surveillance improves outcomes in grafts, and there is limited evidence that surveillance reduces thrombosis without prolonging the life of native fistulae. In conclusion, current evidence does not support the concept that all accesses should undergo routine surveillance with intervention.