Coronary artery stents and non-cardiac surgery
Brighton, UK
* E-mail: carl.kotze{at}gmail.com
Editor—We found the review by Howard-Alpe and colleagues1 interesting and helpful. Recently, there has been much emphasis on point of care platelet function testing, predominantly as a diagnostic aid and in monitoring the effect of antiplatelet agents.2 3 Currently, several avenues of platelet function testing are being explored, of which the majority are mentioned in the review. However, we noted that Multiplate® platelet function analysis (Dynabite GmbH, Munich, Germany), an increasingly recognized platelet analysis technique,4 5 was not mentioned. This analysis is a whole blood test that is based on impedance aggregometry, which measures electrical impedance between two silver-coated copper sensors. As platelets adhere to the sensor wires, impedance increases. The system uses an integrated computer system with five channels which allows for parallel determinations and automatic analysis. Several test reagents are available to allow triggering of different receptors or signal transduction pathways of the platelet, in order to detect its function or response to drugs. Multiplate® differs from Born aggregometry and single platelet5 counting, in that it takes place on surfaces.
Impedance aggregometry revealed a high sensitivity of this method for analysis of aspirin- and clopidogrel-treated patients.6 7 A recent comparison between Multiplate® and a global function analysis using PFA-100 (platelet function analyser) suggests Multiplate® was more specific.4 The use of different activators and the possibility of applying different concentrations of the substances allow the user to vary the sensitivity and specificity as required. However, several questions remain unanswered. A recent study that attempted to classify ‘aspirin non-response’ was unsuccessful due to a high degree of discordance between PFA-100 and impedance aggregometry.8 Further clinical studies are needed to show which parameters of platelet function correlate best with useful clinical endpoints.
Oxford, UK
E-mail: georgina.howard-alpe{at}nda.ox.ac.uk
Editor—We would like to thank Dr Kotze and colleagues for their interesting and informative letter in response to our article.1 Optical light transmission platelet aggregometry, a laboratory-based technique, remains the ‘gold standard’ test for the assessment of platelet function and the inhibition in platelet function caused by various antiplatelet agents. It is interesting to observe the significant result discordance between various point of care platelet function tests with regard to the degree of platelet inhibition provided by different antiplatelet agents. Further studies are definitely warranted to identify the most accurate point of care test available. A reliable measure of the inhibition of platelet function would be extremely useful for anaesthetists. However, at present the accuracy of some of these tests is suboptimal.
References
1 Howard-Alpe GM, de Bono J, Hudsmith L, Orr WP, Foex P, Sear JW. Coronary artery stents and non-cardiac surgery. Br J Anaesth (2007) 98:560–74.
2 Avidan MS, Alcock EL, Da Fonseca J, et al. Comparison of structured use of routine laboratory tests or near-patient assessment with clinical judgement in the management of bleeding after cardiac surgery. Br J Anaesth (2004) 92:178–86.
3 Bracey AW, Grigore AM, Nussmeier NA. Impact of platelet testing on presurgical screening and implications for cardiac and noncardiac surgical procedures. Am J Cardiol (2006) 98:25N–32N.[Web of Science][Medline]
4 Calatzis A, Wittwer M, Krueger B. A new approach to platelet function analysis in whole blood—the Multiplate analyser. Platelets (2004) 15:479–517.[CrossRef][Medline]
5 Tóth O, Calatzis A, Penz S, Losonczy H, Siess W. Multiple electrode aggregometry: a new device to measure platelet aggregation in whole blood. Thromb Haemost (2006) 96:781–8.[Web of Science][Medline]
6 Calatzis A, Spannagl M, Theisen F. Whole blood aggregation in patients on chronic aspirin and/or clopidogrel treatment. Abstract submitted for the GTH congress February 2007; Society of Thrombosis and Haemostasis Research.
7 Weisser H, von Pape K, Dzjan-Horn M, Calatzis A. Control of aspirin effect in cardiovascular patients using two whole blood platelet function assays: PFA-100 and multiple electrode aggregometry. Clin Chem Lab Med (2006) 44:A81–198.[CrossRef]
8 Penz SM, Reininger AJ, Toth O, Deckmyn H, Brandl R, Siess W. Glycoprotein Ib
inhibition and ADP receptor antagonists, but not aspirin, reduce platelet thrombus formation in flowing blood exposed to atherosclerotic plaques. Thromb Haemost (2007) 97:435–43.[Web of Science][Medline]
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