MRA of hemodialysis access grafts and fistulae using selective contrast injection and flow interruption.

MR is a potentially attractive modality for evaluating hemodialysis access anatomy and function. However, the wide range of flow rates in the hemodialysis access complicates interpretation of phase contrast, time-of-flight, and even contrast-enhanced MR angiograms. At high flow rates, signal voids may easily arise at mild narrowings or sharp-angled anastomoses. A method is proposed which visualizes hemodialysis accesses without flow artifacts. Diluted Gd-DTPA is hand-injected directly into the access, while a cuff is used to reduce and subsequently interrupt access flow. Filling of the access is monitored using a fast projection technique with complex subtraction. When filling is satisfactory, a 3D acquisition is started. The feasibility of this selective contrast-enhanced MR angiography technique is demonstrated in four Cimino-fistulae and four PTFE grafts. Magn Reson Med 45:557-561, 2001.

Graft surveillance: venous pressure, access flow, or the combination?

BACKGROUND: Increased venous pressure (VP) and decreased access flow (Qa) are predictors of dialysis access graft thrombosis. VP is easily obtainable. Qa assessment requires a special device and takes more time. The aims of our randomized multicenter studies were to compare outcome in patients with grafts monitored by VP or Qa (study A) or monitored by VP or the combination of VP and Qa (study B). METHODS: We performed VP measurements consisting of weekly VP at a pump flow of 200 mL/min (VP200) and the ratio of VP0/MAP. Qa was measured every eight weeks with the Transonic HD01 hemodialysis monitor. Threshold levels for referral for angiography were VP200> 150 mm Hg or VP0/MAP> 0.5 (both at 3 consecutive dialysis sessions) or Qa <600 mL/min. Subsequent therapy consisted of either percutaneous transluminal angioplasty (PTA) or surgery. RESULTS: Total follow-up was 80.5 patient-years for 125 grafts. The vast majority of a total of 131 positive tests was followed by angiography and corrective intervention. In study A, the rate of thromboses not preceded by a positive test was 0.19 and 0.24 per patient-year (P = NS), and in study B, it was 0.32 versus 0.28 per patient-year (P = NS). Survival curves were not significantly different between the subgroups. CONCLUSIONS: These data demonstrate that standardized monitoring of either VP or Qa or the combination of both and subsequent corrective intervention can reduce thrombosis rate in grafts to below the recommended quality of care standard (that is, 0.5 per patient-year, NKF-DOQI). These surveillance strategies are equally effective in reducing thrombosis rates.

Haemodialysis access: the case for prospective monitoring.

Thrombosis in haemodialysis accesses remains a major problem. It is associated with stenosis that causes haemodynamic and anatomical changes. By prospective monitoring it is possible to identify patients at risk of thrombosis. Those patients should be referred for corrective intervention. This approach can result in a thrombosis rate below the advised quality of care standard of 0.5 thromboses/patient-year.