Hemodialysis access imaging: comparison of flow-interrupted contrast-enhanced MR angiography and digital subtraction angiography.

PURPOSE: To compare flow-interrupted contrast material-enhanced magnetic resonance (MR) angiography with conventional digital subtraction angiography (DSA) for hemodialysis access imaging. MATERIALS AND METHODS: Twenty-two accesses (14 arteriovenous grafts [AVGs], eight arteriovenous fistulas [AVFs]) in 18 consecutive patients were imaged with flow-interrupted contrast-enhanced MR angiography and subsequent conventional DSA. MR image quality was assessed as excellent, good, or nondiagnostic. Anastomotic diameters in AVGs and postanastomotic diameters in AVFs were measured in consideration of an adjacent normal segment. Reductions in the diameter of the lumen and interobserver differences were analyzed with method comparison as described by Bland and Altman and expressed as the mean difference with its 95% confidence limits (CLs) (mean +/- 2 SDs). RESULTS: Image quality obtained with flow-interrupted contrast-enhanced MR angiography was considered excellent in 73% (16 of 22) and good in 23% (5 of 22). Method comparison analysis between MR angiography and DSA indicated a mean difference of 3.2% (95% CLs: -26.7%, 33.1%) for observer 1 and 4.1% (95% CLs: -23.8%, 32.1%) for observer 2. Interobserver analysis at MR angiography indicated a mean difference of 3.2% (95% CLs: -28.8%, 35.2%), and that at DSA indicated a mean difference of 3.6% (95% CLs: -9.4%, 16.7%). CONCLUSION: Image quality and anatomic depiction with flow-interrupted contrast-enhanced MR angiography and with DSA were comparable.

Percutaneous thrombolysis of thrombosed haemodialysis access grafts: comparison of three mechanical devices.

BACKGROUND: Percutaneous thrombolysis has become an accepted treatment of thrombosed haemodialysis grafts. Several devices have been developed for mechanical thrombolysis, which macerate the clot using different mechanisms such as aspiration and fragmentation. The aim of our study was to compare the efficacy of three devices for mechanical thrombolysis in removing the thrombus from thrombosed haemodialysis access grafts and to determine the initial technical and clinical success, complication rates of each device, and graft patency after the procedure. METHODS: Thrombolysis (i.e. clot removal followed by percutaneous transluminal angioplasty (PTA)) was performed in 68 thrombosed haemodialysis grafts using the Cragg brush catheter combined with urokinase in 13, the Hydrolyser in 18 and the Arrow-Trerotola Percutaneous Thrombolytic Device (PTD) in 37. Clot removal scores (CRS, the ability to thoroughly remove clot from the access), initial technical success, clinical success, patency at 30, 60, and 90 days, and complication rates were evaluated. RESULTS: CRS for the Cragg brush, Hydrolyser and PTD were good in 92, 44, and 95% of cases, respectively. Initial technical (85, 83, and 95%) and clinical success (62, 67, and 86%), mean patency rates at 30 (73, 60, and 55%), 60 (61, 53, and 49%), and 90 (49, 40, and 43%) days, stenosis after PTA (33, 46, and 21%) and complication rates (8, 6, and 0%) were not different for the three devices. Success rates and graft patency depended on the effect of PTA, irrespective of the device used. CONCLUSIONS: The rotational devices removed clots more effectively than the Hydrolyser, with the PTD having the advantage of not requiring urokinase. However, the result of PTA in the treatment of underlying stenoses was the only predictive value for graft patency.

Underestimation of access flow by ultrasound dilution flow measurements.

For hemodialysis access surveillance, flow measurements are increasingly considered important because they identify accesses at risk of thrombosis. Usually these flow measurements are performed with the ultrasound dilution technique. In a previous patient study it was observed that the resulting flow values were systematically low as compared to magnetic resonance flow measurements, but a satisfactory explanation was lacking. In the present study, we will demonstrate by hemodynamic calculations and in vitro experiments that this discrepancy can be explained by a temporary reduction of the access flow rate, caused by the reversed needle configuration during ultrasound dilution flow measurements. In this configuration. blood is injected retrogressively at one needle and flow between the needles is increased, causing an increased dissipation of energy. The proposed explanation is subsequently confirmed in a patient with a loop graft, by measuring the blood velocity by Doppler ultrasound as a function of reversed dialyzer flow rate. Apart from the ultrasound dilution technique, these findings are applicable to other recently proposed methods for measuring access flow that employ the reversed needle configuration.

Short- and long-term functional effects of percutaneous transluminal angioplasty in hemodialysis vascular access.

The efficacy of percutaneous transluminal angioplasty (PTA) is usually expressed as the angiographic result. Access flow (Qa) measurements offer a means to quantify the functional effects. This study was performed to evaluate the short-term functional and angiographic effects of PTA and to determine the longevity of the functional effects during the follow-up period. Patients with an arteriovenous graft (AVG) or an arteriovenous fistula (AVF) who were eligible for PTA (Qa values of <600 ml/min) were included. Ultrasound-dilution Qa measurements were obtained shortly before PTA and periodically after PTA, beginning 1 wk after the procedure. The short-term effects were expressed as the increase in Qa and the reduction of stenosis. The long-term effects were expressed as patency and the decrease in Qa after PTA. Ninety-eight PTA procedures for 60 patients (65 AVG and 33 AVF) were analyzed. Qa improved from 371 +/- 17 to 674 +/- 30 ml/min for AVG and from 304 +/- 24 to 638 +/- 51 ml/min for AVF (both P < 0.0001). In 66% (AVG) and 50% (AVF) of cases, Qa increased to levels of >600 ml/min. The degree of stenosis decreased from 65 +/- 3 to 17 +/- 2% for AVG and from 72 +/- 5 to 23 +/- 7% for AVF (both P < 0.005). The reduction of stenosis was not correlated with DeltaQa (r(2) = 0.066). Six-month unassisted patency rates after PTA were 25% for AVG and 50% for AVF. The decreases in Qa were 3.7 +/- 0.8 ml/min per d for AVG and 1.8 +/- 0.9 ml/min per d for AVF. Qa values before PTA and DeltaQa were correlated with the subsequent decrease in Qa (P < 0.005). In conclusion, Qa increases after PTA but, in a substantial percentage of cases, not to levels of >600 ml/min. Qa values before PTA and the increase in Qa were correlated with long-term outcomes, whereas angiographic results were not. These data, combined with literature data, suggest that there is optimal timing for PTA.