2. Georgakarakos E, Ioannou CV, Volanis S, et al. The influence of intraluminal thrombus on abdominal aortic aneurysm wall stress. Int Angiol 2009;28:325e33. 3. Wang DH, Makaroun MS, Webster MW, Vorp DA. Effect of intraluminal thrombus on wall stress in patient-specific models of abdominal aortic aneurysm. J Vasc Surg 2002;36:598e604. 4. Xu XY, Borghi A, Nchimi A, et al. High levels of 18F-FDG uptake in aortic aneurysm wall are associated with high wall stress. Eur J Vasc Endovasc Surg 2010;39:295e301. 5. Wiernicki I, Stachowska E, Safranow K, et al. Enhanced matrix-degrading proteolytic activity within the thin thrombus-covered wall of human abdominal aortic aneu- rysms. Atherosclerosis 2010;212:161e5. DOI: 10.1016/j.avsg.2011.04.013 Comment on the Effect of Aspirin on Adherence of SlimeeProducing, Coagulase-Negative Staphylococci to Vascular Grafts To the Editor: In their study, Demirag and colleagues 1 have reported that salicylic acid at a concentration of 5 mM can inhibit biofilm formation of coagulase-negative staphylococci, re- presented by the standard strain Staphylococcus epidermidis ATCC 12228, on medical biomaterials, such as Dacron (Dacron Boston Scientific Medi-Tech, Watertown, MA) and polytetrafluoroethylene ([PTFE] W. L. Gore, Flagstaff, AZ). The method used consisted in vortexing a 24-hour- incubated sample in medium supplemented or not with salicylic acid, followed by performing colony counts of plated cells on blood agar after an incubation of 24 hours. There is a major concern regarding this study: the stan- dard strain used is not appropriate for such experiments, as S. epidermidis ATCC 12228, known to be a nonpatho- genic strain, is not a biofilm (slime) producer strain because it lacks the ica operon, which is the genetic support of enzymes involved in polysaccharide intercel- lular adhesin synthesis. 2 S. epidermidis RP62A (ATCC 35984), a strain isolated from medical implanteassociated infection, 3 was the stan- dard strain used to establish the effect of salicylic acid on S. epidermidis biofilm in a previous study. 4 Such studies are very important in terms of resolving a major nosocomial infection, but it can give better results with described recommendations. Mohamed Amine Mekni Wafa Achour Assia Ben Hassen, PhD Centre National de Greffe de Moelle Osseuse Bab Saadoun, Tunis, Tunisia E-mail: mekni1983@gmail.com REFERENCES 1. Demirag MK, Esen S, Zivalioglu M, et al. The effect of aspirin on adherence of slime-producing, coagulase-negative staphy- lococci to vascular grafts. Ann Vasc Surg 2007;21:464e7. 2. Holden M, Crossman L, Cerde~ no-T arraga A, Parkhill J. Path- ogenomics of non-pathogens. Nat Rev Microbiol 2004;2:91. 3. Christensen GD, Barker LP, Mawhinney TP, et al. Identifica- tion of an antigenic marker of slime production for Staphylo- coccus epidermidis. Infect Immun 1990;58:2906e11. 4. Muller E, Al-Attar J, Wolff AG, Farbe BF. Mechanism of salic- ylate-mediated inhibition of biofilm in Staphylococcus epidermidis. J Infect Dis 1998;177:501e3. DOI: 10.1016/j.avsg.2011.04.014 Ultrasound Assessment of Morphological and Functional Vessel Parameters Should Be a Mandatory Step Before Arteriovenous Fistula Placement To the Editor: We have read with great interest the article on improved wrist arteriovenous fistula (AVF) outcome by Kim et al., 1 who reported that the radiocephalic vein diameter increased by >0.35 mm on venography, using tourniquet method. They also accentuated that ‘‘ideally, venography results should be compared with those of Doppler scanning.’’ We truly agree with this statement and would like to share our opinion concerning vein distensibility (VD) as an important functional parameter in the prediction of early outcomes of AVF. First, Malovrh 2 reported a better primary patency rate for wrist AVF in patients whose internal vein diam- eter, measured using ultrasound (US) technique, after proximal vein compression increased by 48%, compared with 11.8% in patients with primary AVF failure (P < 0.01). The author also found a high correla- tion between US measurement of internal vein diameter and direct measurement during surgery (r ¼ 0.69, P < 0.01). Second, US as a noninvasive, easily reproducible, safe, and cost-effective method could be used not only in vessel diameter measurements (which are certainly most impor- tant factors in AVF outcome prediction, although reported cutoff values are inconsistent) but also in the measure- ment of the ability of the vein to dilate after proximal vein compression as a functional parameter. Another advantage of US over phlebography and angiography is that contrast agents are not needed, and thus there is no risk for allergic reactions, phlebitis, and deterioration of residual renal function. Our preliminary results on 114 patients regarding the role of vascular functional parameters that influenced the success of primary AVF for hemodialysis were pre- sented in November 2011 at the ASN Kidney meeting in Philadelphia. 3 We showed VD as the most important factor influencing primary AVF patency rates after 4 weeks of maturation. Significant correlation was found between AVF outcome and VD (P ¼ 0.017); also, linear regression was significant for VD (B ¼ 0.517, 95% confi- dence interval: 0.054e0.981, P ¼ 0.029). Vol. 26, No. 3, April 2012 Letters to the Editor 445