Effects of Antiplatelet Drugs on Dialysis-Associated Platelet Deposition in Polytetrafluoroethylene Grafts David W. Windus, MD, Samuel A. Santoro, MD, PhD, Ralph Atkinson, BS, and Henry D. Royal, MD • Hemodialysis is associated with platelet deposition in polytetrafluoroethylene (PTFE) graft fistulas. We deter- mined whether aspirin or ticlopidine would modify this response. Patients on chronic hemodialysis with forearm loop PTFE fistulas were studied. Platelets labeled with 111indium were injected and a baseline scan of the fistula arm was made with a large field of view gamma camera. After a routine dialysis treatment, a second scan was performed within 1 hour. Four weeks later, a repeat labeled platelet study was conducted after taking either aspirin 325 mg/d or ticlopidine 250 mg/d orally for 7 days. Images were computer analyzed by drawing seven standardized regions along each graft. The counts per second per pixel in postdialysis images were compared with predialysis images for each region and a percent uptake compared with the predialysis image was calculated. Regions with dialysis-induced uptake of more than 1.5-fold compared with the predialysis image before antiplatelet drug therapy were compared with these same regions after therapy. Six patients were studied before and after aspirin therapy. Uptakes larger than 1.5-fold over predialysis images were found in 12 of 40 regions and were 292% _+ 50% (±SEM) before and 193% _+ 25% of predialysis values after aspirin (P = 0.02, paired t-test). Uptakes in the remaining regions were 107% ± 4% before and 115% _+ 6% after aspirin (P = NS). A second group was studied before and after ticlopidine (n = 5). Uptakes increased by more than 1.5-fold compared with predialysis images in 19 of 30 regions and had a median of 286% increased uptake (mean, 785% _+ 374%) before and 160% (153% + 10%) after drug therapy (P < 0.001, Wilcoxon). Uptakes in the remaining regions were 116% ± 5% before and 134% _+ 13% after drug therapy (P = NS). Platelet aggregation studies suggested compliance with both drugs. These studies show that these antiplatelet drugs reduce, but do not completely prevent, dialysis-associated radiolabeled platelet deposition in PTFE grafts. © 1997 by the National Kidney Foundation, Inc. INDEX WORDS: Platelets; aspirin; ticlopidine; platelet aggregation; polytetrafluoroethylene. T HE pathophysiology of hemodialysis fistula thrombosis is not completely understood and is probably multifactorial. Hypotheses ex- plaining the problem have focussed on factors causing blood flow impedance and subsequent blood clotting. These include venous outflow ste- nosis due to neointimal hyperplasia and external compression. An additional mechanism may in- clude hemodialysis-associated platelet deposition in polytetrafluoroethylene (PTFE) grafts.l'2 Much attention has been given to pharmaco- logic prevention of fistula thrombosisY ° Early studies suggested that aspirin, ticlopidine, and From the Renal Division and the Division of Laboratory Medicine, Washington University School of Medicine, St Louis, MO; and the Division of Nuclear Medicine, Mallin- krodt Institute of Radiology, St Louis, MO. Received June 27, 1996; accepted in revised form Decem- ber 12, 1996. Supported in part by US Public Health Services National Institute of Diabetes and Digestive and Kidney Diseases Grant No. DK 45676. Address reprint requests to David W. Windus, MD, Wash- ington University, 660 S Euclid Ave, Box 8129, St Louis, MO 63110. © 1997 by the National Kidney Foundation, Inc. 0272-6386/97/2904-0011 $3.00/0 sulfinpyrazone might be useful in the prevention of clotting in Scribner shunts, recently placed native vein fistulas, and in patients with recurrent vascular access thromboses. 58 More recently, Sreedhara et al 1° reported that dipyridamole, but not aspirin, reduced thrombosis of PTFE graft fistulas in hemodialysis patients with no prior complications. Neither drug was effective in pa- tients with prior episodes of clotting. No other large-scale studies of antithrombotic drugs have been reported in patients with PTFE graft fistulas. These studies are difficult because of the large numbers of subjects required, the potential side effects of anticoagulant medications, and the costs. Using an indium-labeled platelet technique, we recently reported that dialysis was associated with platelet deposition in PTFE graft fistulas. 2 We speculated that this method might be used to screen antiplatelet drugs for efficacy in dialysis patients. The purpose of this study was to quan- tify the effects of aspirin and ticlopidine on he- modialysis-induced platelet deposition in PTFE graft fistulas. MATERIALS AND METHODS Hemodialysis was performed using a blood flow rate of 400 to 450 mL/min and reprocessed regenerated cellulose 560 American Joumal of Kidney Diseases, Vol 29, No 4 (April), 1997: pp 560-564