FP649IN SEARCH OF AN OPTIMAL SCREENING PROGRAM FOR DETECTING STENOSIS AND PREDICTING THROMBOSIS IN ARTERIOVENOUS GRAFT: A DIAGNOSTIC COMPARATIVE ANALYSIS OF THE CURRENTLY AVAILABLE TOOLS

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INTRODUCTION: Guidelines recommend routine screening of arteriovenous grafts for timely detection and elective repair of significant (>50%) stenosis (ST) at high risk of thrombosis by surveillance (access blood flow [Qa], static venous pressure ratio [sVPR] or Duplex Ultrasound [DU]) or clinical monitoring [M]. They also state that there is insufficient evidence to prefer one tool to another due to the lack of studies comparing vis-a-vis all of the options. To identify an optimal screening program we compared the diagnostic performance of the available screening tool in detecting ST at angiography (STA) and predicting incipient thrombosis (within 4-month) in the same population of 62 grafts. METHODS: Diagnostic performance of the screening tools was evaluated by the Area under Reeceiver Operator Curve (AUC[95% CI]) and Cox's multivariate analysis was used to identify predictors of thrombosis. RESULTS: M was unable to detect STA (AUC:0.58[044-0.72], p=0.277), while dynamic venous (dVP) and arterial (dAP/Qb) pressures and all surveillance tools showed excellent-to-good accuracy for STA with no significant difference between one or another: Qa by ultrasound dilution (QaU) (AUC:0.86[0.77-0.95]),ST at DU (STD)(AUC:0.82[0.71-0.93]), sVPR (AUC:0.76[0.65-0.88]), dAP/Qb (AUC: 0.71[0.59-0.84]), Qa at DU (QaD)(AUC:0.70[0.59-0.82]), and dVP (AUC:0.68[0.56-0.81]) (p<0.01). In a model including all screening tools, STA, STD, and acute symptomatic hypotensive episodes (AH) during the follow-up, the only significant and independent predictors of incipient thrombosis were AH (relative risk (RR) 6.8[95%CI:3.2-15.7]) and QaU (RR 16%[8-21] for each 100 ml/min drop in Qa) or QaD (RR 13%[5-17] for each 100 ml/min drop in Qa)(p<0.001). The risk of thrombosis increased significantly when both QaU or QaD dropped below 1000 ml/min (p<0.001), while the risk of thrombosis attributable to AH was 78%[95%CI:62-94] at Qa>1000 ml/min and 26%[11-41] at Qa<1000 ml/min. CONCLUSIONS: Our comparative analysis shows that in graft an optimal screening program may be based on Qa measurement alone (by ultrasound dilution technique or DU) because of its excellent-to-good accuracy in detecting ST and predicting incipient thrombosis, and suggests that the risk of thrombosis may be contained by avoiding acute hypotensive episodes and using a Qa threshold of <1000 ml/min for elective stenosis repair.

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