Screening for subclinical stenosis in native vessel arteriovenous fistulae.

Guidelines recommend the use of ultrasound dilution techniques (UDT), including measurement of access recirculation (AR) and access blood flow (Q(a)), to screen for subclinical vascular access dysfunction. Although these techniques are efficacious in polytetrafluoroethylene grafts, data in native vessel arteriovenous fistulae (AVF) are lacking. A prospective observational study was conducted to evaluate the utility of UDT screening in AVF. Q(a) and AR were measured bimonthly. Positive studies required fistulograms and were defined by Q(a) < 500 ml/min, DeltaQ(a) > 20% from baseline or AR > 5%. Accesses with stenosis underwent percutaneous angioplasty. After 1 yr, there were 1355 mo of follow-up in 177 patients. There were 44 positive studies in 40 patients. Q(a) was <500 ml/min in 36 (82%), DeltaQ(a) was >20% in 5 (11%), and AR was >5% in 6 (14%). Of patients with Q(a) < 500 ml/min, 29 (81%) had stenosis. Only two patients (40%) with DeltaQ(a) > 20% but Q(a) > 500 ml/min had stenosis. No patient with AR > 5% had stenosis unless Q(a) was also <500 ml/min. Immediate patency rate was 93% post-PTA. Mean Q(a) increased from 303 +/- 154 ml/min to 602 +/- 220 ml/min (P < 0.0001), and mean urea reduction ratio increased from 70.4 +/- 8.4% to 74.6 +/- 6.5% (P = 0.003) post-PTA. The results demonstrate that UDT could detect subclinical stenoses in AVF, and most lesions were amenable to angioplasty. AVF that underwent PTA delivered higher Q(a) and urea reduction ratio, and immediate patency rates were acceptable. Access failure after negative UDT was unusual. Measuring AR increases the time required to perform UDT but does not improve utility. Serial measurements of Q(a) alone may be the best strategy for screening AVF.