Point-of-care platelet function assays demonstrate reduced responsiveness to clopidogrel, but not aspirin, in patients with Drug-Eluting Stent Thrombosis whilst on dual antiplatelet therapy
© Hobson et al; licensee BioMed Central Ltd. 2008
Received: 21 December 2007
Accepted: 29 February 2008
Published: 29 February 2008
To test the hypothesis that point-of-care assays of platelet reactivity would demonstrate reduced response to antiplatelet therapy in patients who experienced Drug Eluting Stent (DES) ST whilst on dual antiplatelet therapy compared to matched DES controls. Whilst the aetiology of stent thrombosis (ST) is multifactorial there is increasing evidence from laboratory-based assays that hyporesponsiveness to antiplatelet therapy is a factor in some cases.
From 3004 PCI patients, seven survivors of DES ST whilst on dual antiplatelet therapy were identified and each matched with two patients without ST. Analysis was performed using (a) short Thrombelastogram PlateletMapping™ (TEG) and (b) VerifyNow Aspirin and P2Y12 assays. TEG analysis was performed using the Area Under the Curve at 15 minutes (AUC15) as previously described.
There were no differences in responses to aspirin. There was significantly greater platelet reactivity on clopidogrel in the ST group using the Accumetrics P2Y12 assay (183 ± 51 vs. 108 ± 31, p = 0.02) and a trend towards greater reactivity using TEG AUC15 (910 ± 328 vs. 618 ± 129, p = 0.07). 57% of the ST group by TEG and 43% of the ST cases by Accumetrics PRU had results > two standard deviations above the expected mean in the control group.
This study demonstrates reduced platelet response to clopidogrel in some patients with DES ST compared to matched controls. The availability of point-of-care assays that can detect these responses raises the possibility of prospectively identifying DES patients at risk of ST and manipulating their subsequent risk.
Robust evidence demonstrating the ability of drug-eluting stent (DES) technology to reduce restenosis in comparison to bare metal stents (BMS) has led to widespread DES uptake. Balanced against this significant clinical benefit, however, is concern about the incidence of stent thrombosis (ST) in DES patients. Observational and randomised trial data suggest that there is a cumulative incidence of ST in DES patients of between 0.5%–1% per year [1, 2], correlating in some series with a similar rate of death and myocardial infarction .
There are well established procedural risk factors for ST such as stent under-deployment , length of stented segment , and idiosyncratic factors including a form of hypersensitivity . However, the inappropriate termination of aspirin and clopidogrel therapy appears to be particularly hazardous . In DES patients there is therefore an important reliance for some (as yet undetermined) period of time on dual antiplatelet therapy [8, 9], possibly as a result delayed stent endothelialisation . This requirement for ongoing dual antiplatelet therapy, together with evidence of considerable biological variability in the response of individuals to antiplatelet therapies, particularly clopidogrel [11, 12], and association between poor response and adverse cardiovascular outcome [13, 14] has raised the important question: can poor responses to these agents render some individuals at risk of DES ST? There is now growing evidence from laboratory based assays that variability in the response to antiplatelet agents, particularly clopidogrel, can contribute to ST in DES patients [15–21].
Typically, clopidogrel is given in standard doses to patients receiving DES, despite both experimental and clinical data demonstrating important biological variation in response. However, clinical detection of reduced responsiveness to clopidogrel and/or aspirin has been hampered both by a lack of point-of-care assays and by an appropriate definition of what constitutes "resistance" .
The purpose of this study was to test the hypothesis that platelet reactivity whilst on aspirin and clopidogrel, assessed using two near patient assays, a novel modification of Thrombelastograph® (TEG) PlateletMapping™  and Accumetrics VerifyNow™, would be significantly greater in a consecutive group of patients who survived DES ST than in matched DES controls.
Approval was obtained from the Isle of Wight, Portsmouth & South East Hampshire Research Ethics committee prior to commencing the study (Ref: 06/Q1701/49). All subjects provided written informed consent.
Twenty-two patients with DES ST were identified from a consecutive series of 3004 patients, 90% of whom received DES, over a 2 year period at this centre . Seven cases (four subacute and three late) were identified where ST occurred in the context of dual antiplatelet therapy with both aspirin and clopidogrel and in whom dual antiplatelet therapy was on-going. None of the cases were taking additional antiplatelet therapy, anticoagulants or non-steroidal anti inflammatory medication.
61.9 ± 5.7
61.8 ± 4.3
Sex (% Male)
Emergency cases (%)
Elective cases (%)
ACS cases (%)
Stent length (mm)
26.7 ± 11.3
27.9 ± 6.3
Minimum stent diameter (mm)
2.8 ± 0.3
2.9 ± 0.3
Aspirin dose (mg)
140 ± 21.0
140 ± 13.4
Clopidogrel dose (mg)
86 ± 21
Duration of clopidogrel (days)
161 ± 163
77 ± 28
Time from latest event/intervention (days)
145 ± 84
76 ± 28
Statin (% total/% Atorvastatin)
Hb conc. (g/l)
130 ± 13
137 ± 10
0.39 ± 0.03
0.40 ± 0.03
262 ± 42
229 ± 25
1.1 ± 0.1
1.0 ± 0.0
67 ± 8
64 ± 4
In all subjects venesection was performed from the antecubital fossa using an 18 gauge needle and a lightly applied tourniquet and the first 2 mls of blood discarded. Blood was then drawn into a 6 ml Lithium Heparin Vacutainer® for TEG analysis and two 2 ml 3.2% sodium citrate Vacutainers® for VerifyNow analysis.
samples were analysed using TEG PlateletMapping™ (Haemoscope Corp, IL, USA) according to the manufacturer's instructions. For each trace the maximum amplitude (MA) was obtained from the standard analysis package and the Area under the response curve at 15 minutes (AUC15) calculated using a software programme (Areafinder 2:1) and method of analysis developed and previously described by this group [23, 25].
VerifyNow™ Aspirin and P2Y12 assays were analysed for each individual according to manufacturer's instructions to obtain the aspirin response units (ARU) and platelet response units (PRU) respectively.
For TEG samples comparisons were made between the MA and AUC15 for each individual channel in the 2 groups. The percentage platelet inhibition (%PIn) and percentage clotting inhibition (%CIn) were calculated for both aspirin (using the channel with Arachidonic Acid (AA) stimulation) and clopidogrel (using Adenosine DiPhosphate (ADP) stimulation) from each sample [23, 26]. For Accumetrics comparisons were made between the ARU and PRU.
Expert statistical advice was obtained prior to the commencement of the study. Data are presented as the mean and 95% confidence interval of the mean. Significance between the groups was determined using two group t-tests for continuous variables and χ2 (chi squared) tests for categorical data with a p value of < 0.05 (2-tailed) considered to represent significance.
Baseline demographics are shown in Table 1. There were no significant differences between the 2 groups which were well matched, nor were there any significant differences in baseline haematological variables between the 2 groups (Table 2).
Responses to aspirin
There was no significant difference in responses assessed with AA-stimulation between the ST group and control group in (i) %PIn (79.6 ± 20.8 vs. 89.9 ± 7.6, p = 0.39); %CIn (75.2 ± 9.4 vs. 75.9 ± 6.0, p = 0.90); (ii) MA of the AA channel (25.3 ± 17.6 vs. 14.0 ± 4.5, p = 0.26) or (iii) AUC15 of the AA channel (244 ± 113 vs. 216 ± 56, p = 0.67).
There was no significant difference between ARU measurements in the ST group and controls (453 ± 50 vs 410 ± 29, p = 0.18).
Responses to Clopidogrel
Other TEG variables
There were no significant differences between cases and controls in TEG variables which have been previously identified as predictive of ischaemic events after PCI (i.e. MA of the Thrombin channel (61.6 ± 2.9 vs. 64.1 ± 2.7, p = 0.21) and the R time of the Thrombin channel (6.9 ± 1.5 vs. 7.1 ± 2.0, p = 0.84)) .
The hypothesis for this study was that these two point-of-care tests (VerifyNow and a novel modification of TEG that produces a result after only 15 minutes) could detect reduced responsiveness to antiplatelet therapy in survivors of ST whilst on dual antiplatelet therapy compared to matched controls. This hypothesis has been disproved in the case of aspirin but proved for clopidogrel using Accumetrics with a trend towards significance using TEG AUC15. Our results suggest that clopidogrel, but not aspirin, resistance contributes to ST in some cases.
The implications of this study are clinically relevant. Firstly, they add to the growing concern that some patients receiving DES may be intrinsically at risk of ST because of their relative lack of response to clopidogrel. Secondly, there are now two point-of-care assays available that allow rapid detection of the response of prospective DES patients to clopidogrel, raising the possibility that such "at risk" individuals could be detected in routine clinical practice, before they are exposed to the potentially suboptimal combination of DES and standard doses of antiplatelet drugs. We found that approximately 50% of patients with previous ST whilst on clopidogrel had abnormally high reactivity whilst on clopidogrel with both Accumetrics and TEG (PRU and TEG AUC15 of ADP channel > 2 standard deviations above the expected means). Further data are now required to determine (a) whether the responses of such individuals to antiplatelet therapy can be normalised by interventions such as increasing the maintenance dose of clopidogrel , or through the use of alternative or additional antiplatelet agents [28, 29], and (b) whether prospectively screening large populations of patients undergoing percutaneous intervention using such tests to guide therapy can decrease ST rates.
This study has important limitations. Firstly, the absolute number of ST patients is low. Nevertheless, the ST population in this study was derived from a consecutive series of 3004 DES patients at a single centre. Secondly, as this is a retrospective study we do not have baseline samples prior to the initiation of antiplatelet therapy for calculation of a response to antiplatelet therapy compared to baseline. Instead we utilised the clinically important measure of platelet reactivity whilst on antiplatelet treatment. Thirdly, studies recruiting patients who have survived ST will inevitably be weaker for the absence of data relating to patients who died as a result of ST. Lastly we did not test for evidence of drug compliance in this study.
Using assays suitable for point-of-care use in routine clinical practice, this study demonstrates an association between reduced responses to clopidogrel, but not aspirin, in a proportion of DES ST patients when compared to matched DES patients without ST. These findings are in keeping with recent studies using laboratory based research tools. The availability of two point-of-care assays that can be employed to detect such responses raises the possibility of detecting clopidogrel hypo-responsiveness prior to DES implantation and possibly manipulating the risk of subsequent ST. Further data are required.
We acknowledge the clinical support of Drs Calver, Gray and Simpson, the support of the Wellcome Trust Clinical Research Facility and Medical Statistician Dr G Yadegarfar. Sources of funding: Unrestricted research grants from Boston Scientific Corporation, Haemoscope Corporation and Medicell Ltd. Funding sources had no role in study design, result acquisition, data analysis, manuscript preparation or decision to submit for publication.
- Nordmann AJ, Briel M, Eucher HC: Mortality in randomised controlled trials comparing drug-eluting vs bare metal seats in coronary disease: a metanalysis. Eur Heart J 2006, 27: 2784-814. 10.1093/eurheartj/ehl282View ArticlePubMedGoogle Scholar
- Daemen J, Wenawesar P, Tsuchida K, Abracht L, Vaina S, Morger C, Kukreja N, Juni P, Sianos G, Hellige G, van-Domburg RT, Hess OM, Boersma E, Meier B, Windecher S, Serruys PW: Early and late coronary stent thrombosis of sirolimus-eluting and paclitaxel-eluting stents in routine clinical practice: data from a large two-institutional cohort study. Lancet 2007, 369: 667-678. 10.1016/S0140-6736(07)60314-6View ArticlePubMedGoogle Scholar
- Lagerqvist B, James S, Stenestrand U, Lindback J, Nilsson T, Wallentin L: Long-term outcomes for drug-eluting stents versus bare metal stents in Sweden. N Engl J Med 2007, 359: 1009-19. 10.1056/NEJMoa067722View ArticleGoogle Scholar
- Fujii K, Carlier S, Mintz G, Yang Y, Moussa I, Weisz G, Dangas G, Mehran R, Lansky AJ, Kreps EM, Collins M, Stone GW, Moses JW, Leon MB: Stent underexpansion and residual reference vessel stenosis are associated with stent thrombosis after successful sirolimus-eluting stent implantation. J Am Coll Cardiol 2005, 45: 995-8. 10.1016/j.jacc.2004.12.066View ArticlePubMedGoogle Scholar
- Moreno R, Fernandez C, Hernandez R, Alfonso F, Angiolillo DJ, Sabate M, Escaned J, Banuelos C, Fernandez OA, Macaya C: Drug-eluting stent thrombosis: results from a pooled analysis including 10 randomised trials. J Am Coll Cardiol 2005, 45: 954-9. 10.1016/j.jacc.2004.11.065View ArticlePubMedGoogle Scholar
- Virmani R, Guagliumi G, Farb A, Musumeci G, Grieco N, Motta T, Mihalcsik L, Tespitli M, Valsecchi O, Kolodgie FD: Localized hypersensitivity and late coronary thrombosis secondary to a sirolimus-eluting stent: should we be cautious? Circulation 2004, 109: 701-5. 10.1161/01.CIR.0000116202.41966.D4View ArticlePubMedGoogle Scholar
- Iakovou I, Schmidt T, Bonizzoni E, Ge L, Sangiorgi GM, Stankovic G, Airoldi F, Chieffo A, Montorfano M, Carlino M, Michev I, Corvaja N, Briguori C, Gerckens U, Grube E, Columbo A: Incidence, Predictors, and Outcome of Thrombosis After Successful Implantation of Drug-Eluting Stents. JAMA 2005, 293: 2126-2130. 10.1001/jama.293.17.2126View ArticlePubMedGoogle Scholar
- Jeremias A, Sylvia B, Bridges J, Kirtane AJ, Bigelow B, Pinto DS, Ho KKL, Cohen DJ, Garcia LA, Cutlip DE, Carrozza JP Jr: Stent thrombosis after successful sirolimus-eluting stent implantation. Circulation 2004, 109: 1930-2. 10.1161/01.CIR.0000127105.99982.21View ArticlePubMedGoogle Scholar
- Marret E, Collet J, Albaladejo P, Montalescot G: Thrombosis after implantation of drug-eluting stents. JAMA 2006, 295: 36. 10.1001/jama.295.1.36-aPubMedGoogle Scholar
- Luscher T, Steffel J, Eberli F, Joner M, Nakazowa G, Tanner F, Virmani R: Drug-eluting stents and coronary thrombosis. Biological mechanisms and clinical implications. Circulation 2007, 115: 1051-58. 10.1161/CIRCULATIONAHA.106.675934View ArticlePubMedGoogle Scholar
- O'Donohue M, Wiviott S: Clopidogrel response variability and future therapies: clopidogrel does one size fit all? Circulation 2006, 114: e600-6. 10.1161/CIRCULATIONAHA.106.643171View ArticleGoogle Scholar
- Jaremo P, Lindahl TL, Fransson SG, Richter A: Individual variations of platelet inhibition after loading doses of clopidogrel. J Intern Med 2002, 252: 233-238. 10.1046/j.1365-2796.2002.01027.xView ArticlePubMedGoogle Scholar
- Gurbel PA, Bliden KP, Hiatt BL, O'Connor CM: Clopidogrel for coronary stenting: response variability, drug resistance and the effect of pre-treatment platelet reactivity. Circulation 2003, 107: 2908-2913. 10.1161/01.CIR.0000072771.11429.83View ArticlePubMedGoogle Scholar
- Gurbel PA, Bliden KP, Gruger K, Cho PW, Zaman KA, Kreutz PR, Bassi AK, Tantry US: Platelet Reactivity in Patients and Recurrent Events Post-Stenting: Results of the PREPARE POST-STENTING STUDY. J Am Coll Cardiol 2005, 46: 1820-6. 10.1016/j.jacc.2005.07.041View ArticlePubMedGoogle Scholar
- Mueller I, Besta F, Schulz C, Massberg S, Schonig A, Gawaz M: Prevalence of clopidogrel non-responders among patients with stable angina pectoris scheduled for elective stent placement. Thromb Haemost 2003, 89: 783-7.Google Scholar
- Barragan P, Bouvier JL, Roquebert PO, Maculuso G, Commeau P, Comet B, Lafont A, Camoin L, Walter U, Eigenthaler M: Resistance to thienopyridines: clinical detection of coronary Stent Thrombosis by monitoring of Vasodilator-Stimulated Phosphoprotein Phosphorylation. Catheter Cardiovasc Intev 2003, 59: 295-302. 10.1002/ccd.10497View ArticleGoogle Scholar
- Gurbel PA, Bliden KP, Samara W, Yoho JA, Hayes K, Fissha MZ, Tantry US: Clopidogrel effect on platelet reactivity in patients with stent thrombosis: results of the CREST Study. J Am Coll Cardiol 2005, 46: 1827-1832. 10.1016/j.jacc.2005.07.056View ArticlePubMedGoogle Scholar
- Wenaweser P, Dorffler MJ, Imboden K, Windecker S, Togni M, Meier B, Haeberli A, Hess OM: Stent thrombosis is associated with an impaired response to antiplatelet therapy. J Am Coll Cardiol 2005, 45: 1748-1752. 10.1016/j.jacc.2005.01.058View ArticlePubMedGoogle Scholar
- Ajzenberg N, Aubry P, Huisse MG, Cachier A, El Amara W, Feldman LJ, Himbert D, Barcich D, Guillin M, Steg P: Enhanced Shear-induced Platelet Aggregation in patients who experience subacute stent thrombosis: a case control study. J Am Coll Cardiol 2005, 45: 1753-1756. 10.1016/j.jacc.2004.10.079View ArticlePubMedGoogle Scholar
- Buonamici P, Marcucci R, Migliorini A, Gensini GF, Santini A, Paniccia R, Moschi G, Gori AM, Abbate R, Antoniucci D: Impact of Platelet Reactivity After Clopidogrel Administration on Drug-Eluting Stent Thrombosis. J Am Coll Cardiol 2007, 49: 2312-7. 10.1016/j.jacc.2007.01.094View ArticlePubMedGoogle Scholar
- Ruef J, Kranzhofer R: Coronary stent thrombosis related to aspirin resistance: what are the underlying mechanisms? J Interv Cardiol 2006, 19: 507-9. 10.1111/j.1540-8183.2006.00196.xView ArticlePubMedGoogle Scholar
- Alfonso F, Angiolillo D: Platelet function assessment to predict outcomes after coronary interventions: hype or hope? J Am Coll Cardiol 2006, 48: 1751-4. 10.1016/j.jacc.2006.08.009View ArticlePubMedGoogle Scholar
- Hobson AR, Petley GW, Dawkins KD, Curzen NP: A Novel Fifteen Minute Test for Assessment of Individual Time-dependent Clotting Responses to Aspirin and Clopidogrel using Modified Thrombelastography. Platelets 2007, 18: 497-505. 10.1080/09537100701329162View ArticlePubMedGoogle Scholar
- Curzen NP, Morton G, Hobson AR, Simpson I, Calver A, Gray H, Dawkins KD: Stent thrombosis and antiplatelet therapy: a review of 3004 consecutive patients in a single centre. Br J Cardiol 2007, 14: 234-6.Google Scholar
- Swallow RA, Agarwala RA, Dawkins KD, Curzen NP: Thrombelastography: a novel bedside tool to assess the effects of antiplatelet therapy? Platelets 2006, 17: 385-392. 10.1080/09537100600757521View ArticlePubMedGoogle Scholar
- Craft R, Chavez J, Bresee S, Wortham DC, Cohen E, Carroll RC: A Novel modification of the Thrombelastograph assay, isolating platelet function, correlates with optical platelet aggregation. J Lab Clin Med 2004, 143: 301-9. 10.1016/j.lab.2004.01.011View ArticlePubMedGoogle Scholar
- Angiolillo DJ, Shoemaker SB, Desai B, Yuan H, Charlton RK, Bernardo E, Zenni MM, Guzman LA, Bass TA, Costa MA: Randomized study of a high clopidogrel maintenance dose in patients with diabetes mellitus and coronary artery disease: results of the Optimising Antiplatelet Therapy in Diabetes Mellitus (OPTIMUS) study. Circulation 2007, 115: 708-16. 10.1161/CIRCULATIONAHA.106.667741View ArticlePubMedGoogle Scholar
- Wiviott SD, Braunwald E, McCabe CH, Montalescot G, Ruzyullo W, Gottleib S, Neumann FJ, Ardissino D, De Servi S, Murphy S, Riesmeyer J, Weerakkody G, Gibson M, Antman EM, for the TRITON-TIMI 38 Investigators: Prasugrel versus Clopidogrel in patients with acute coronary syndromes. N Engl J Med 2007, 357: 2001-15. 10.1056/NEJMoa0706482View ArticlePubMedGoogle Scholar
- Lee SW, Park SW, Hong MK, Kim YH, Lee BK, Song JM, Han KH, Lee CW, Kang DH, Song JK, Kim JJ, Park SJ: Triple versus dual antiplatelet therapy after coronary stenting: impact on stent thrombosis. J Am Coll Cardiol 2005, 46: 1833-7. 10.1016/j.jacc.2005.07.048View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.