Validation of QB stress test as a useful tool in the detection of native arteriovenous fistula stenosis: results after 22 months of follow-up.

Background: Access flow (QA) surveillance is the best method recommended for early stenosis detection, but in native arteriovenous fistula (AVF), the literature is conflicting about the real need for monthly monitoring of QA, as suggested by the K-DOQI Guidelines.

Methods: From 1 January 2006 to 31 October 2007 (mean 18.0 +/- 4.9 months), we prospectively followed up 224 patients with monthly AVF monitoring by means of clinical examination and QB stress test (QBST). Suspected malfunctioning AVFs were referred to ultrasound dilution technique (UDT) and imaging techniques (Doppler ultrasonography, angiography), with eventually further percutaneous angioplasty (PTA) or surgical revision.

Results: We observed a good correlation between QBST and QA measurement obtained by the UDT. Patients with positive QBST had a lower QA than negative QBST subjects (433 +/- 203 vs 1168 +/- 681 ml/min, P < 0.0001). Fifty-four out of 224 (24%) patients were selected for possibly malfunctioning AVF. We found no stenosis in 13 out of 54 (24%) patients, inflow stenosis in 29 out of 54 (54%) patients and outflow stenosis in 12 out of 54 (22%) patients. The QBST positive predictive value for inflow stenosis was 76.3%. The interventional radiologist performed 38 PTA procedures in 33 patients (11 PTA per 100 patient-years) and we surgically created 13 new AVF (3.7 per 100 patient-years). Only five thrombosis episodes occurred in five patients during the follow-up (1.5 thromboses per 100 patient-years).

Conclusions: QBST is a simple, low-cost, not time-consuming test, able to select, together with clinical evaluation, malfunctioning AVF with stenosis located specifically in the inflow tract. Our follow-up data demonstrated that it is possible to achieve a low AVF thrombosis rate by adding QBST in an AVF monitoring program, thus reducing the surveillance burden.