Short Thrombelastography Research Articles

Comparison of the antiplatelet and antithrombotic effects of bivalirudin versus unfractionated heparin: A platelet substudy of the HEAT PPCI trial

In randomised trials, bivalirudin has been associated with higher rates of acute stent thrombosis (AST) compared to unfractionated heparin (UFH), without mechanistic explanation. Furthermore, data are discrepant regards the antiplatelet effects of bivalirudin. This prespecified study, part of a larger HEAT-PPCI Platelet Substudy, aimed to compare the antiplatelet and antithrombotic effects of bivalirudin and UFH using short thrombelastography (s-TEG), an ex vivo whole blood platelet function assay. In HEAT-PPCI, patients were randomised to receive UFH or bivalirudin before angiography. Assay with s-TEG was performed in 184 patients (10.2%) at end of procedure (EOP) and repeated at 24 h. In addition to adenosine diphosphate- (ADP) and arachidonic acid- (AA) mediated platelet aggregation, thrombin-mediated clotting (TMC) was assessed using kaolin with and without heparinase. There were no significant differences between UFH and bivalirudin in ADP- and AA-mediated platelet aggregation at EOP or 24 h. Whilst UFH obliterated TMC at EOP, bivalirudin prolonged R time (19.7 min [15.9–25.4] vs. 8.4 min [7.5–10]; P < 0.0001), K time (2.4 min [1.9–3.4] vs. 2.2 min [1.8–2.7]; P = 0.007) and significantly increased maximum clot strength (MA 62.7 mm [58.7–67.4] vs. 58.6 [55–63]; P = 0.0005), compared to control. In conclusion, there were no significant differences in the antiplatelet effects of UFH and bivalirudin. However, whilst UFH obliterated TMC, bivalirudin prolonged clot initiation but potentiated maximum clot strength. As AST is likely multifactorial in aetiology, in patients treated with bivalirudin, increased clot strength may contribute to this hazard in some individuals and this observation warrants further investigation.

Does the response to aspirin and clopidogrel vary over 6 months in patients with ischemic heart disease?

Dual-antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor, mostly clopidogrel, is the default therapy in both acute coronary syndrome (ACS) and after intracoronary stents. It is well established that responses to antiplatelet therapy (APT), particularly clopidogrel, are subject to considerable interindividual variability. We investigated whether responses to APT in individuals vary significantly over time. Simultaneous assay with VerifyNow(™) and short thrombelastography (s-TEG) was performed before and at four time points over 6 months after hospital discharge in 40 patients receiving DAPT. Serum thromboxane B2 levels were also measured. While aspirin response units (ARU) by VerifyNow(™) and serum thromboxane B2 levels remained stable over time, arachidonic acid (AA)-mediated platelet aggregation with s-TEG (i.e. area under the curve at 15 min in AA channel, AUC15AA ) increased at 1 week compared with predischarge (P < 0.008). In addition, platelet reactivity units (PRU) by VerifyNow(™) (P = 0.046) and adenosine diphosphate (ADP)-mediated platelet aggregation with s-TEG (i.e. AUC15ADP ) also increased at 1 week compared with predischarge (P = 0.026). There were no significant changes in either platelet reactivity or rates of high on-treatment platelet reactivity while receiving clopidogrel beyond 1 week. This study demonstrates important variability in responses to APT within individuals between predischarge and 1 week but not thereafter. The use of a single early (predischarge) platelet function assay as an indicator of future response may therefore be flawed. The design of future strategies to assess individual responses for tailored therapy needs to take this into account.

Does the VerifyNow P2Y12 assay overestimate “therapeutic response” to clopidogrel?

In contrast to short thrombelastography (s-TEG) which utilises adenosine diphosphate (ADP) alone, the VerifyNow P2Y12 assay (VN-P2Y12) additionally uses prostaglandin E1 (PGE1) as agonist to assess response to P2Y12 inhibitors. Based upon previous observations, we hypothesised that VN-P2Y12 overestimates the therapeutic effects of clopidogrel. Simultaneous assay with s-TEG and VN-P2Y12 was performed in 43 healthy volunteers and 170 patients either on or off clopidogrel. Furthermore, in 27 patients on clopidogrel 75 mg we compared the effects of adding 22 nM PGE1 to ADP on platelet aggregation in s-TEG to ADP alone. A higher proportion of individuals had a result indicating high platelet reactivity (HPR) with s-TEG than VN-P2Y12 in (i) 43 clopidogrel naïve volunteers (95.3% vs 81.4%, p = NS); (ii) 28 volunteers loaded with clopidogrel 600 mg (39.3% vs 10.7 %, p = < 0.01); (iii) 123 clopidogrel naïve patients (93.5% vs 78%, p = < 0.0001); (iv) 47 patients on clopidogrel 75 mg (42.6% vs 4.3%, p = < 0.0001). In 59 patients loaded with clopidogrel 600 mg/900 mg, a greater proportion had a "therapeutic response" with VN-P2Y12 compared to s-TEG, regardless of the threshold for defining HPR with VN-PY12 (P2Y12 reaction units ≥ 230 or 208). Furthermore, adding PGE1 to ADP in s-TEG potentiated the anti-aggregatory effects of clopidogrel compared with ADP alone. In conclusion, VN-P2Y12 overestimates the functional effects of clopidogrel in some individuals, possibly because it utilises PGE1 in addition to ADP. This could have implications for the ability of VN-P2Y12 to stratify patients as "responders" or "non-responders" to clopidogrel.

“Aspirin Resistance” in Ischemic Stroke: Insights Using Short Thrombelastography

Aspirin achieves its antithrombotic effect through inactivation of cyclo-oxygenase (COX)-1, thereby preventing generation of thromboxane (TX)A2 from arachidonic acid (AA). The reported prevalence of aspirin "resistance" varies significantly and is usually based on platelet function tests (PFTs) that use AA-induced platelet reactivity as a surrogate measure of the effect of aspirin, rather than specific assessment of its effect on its therapeutic target (ie, COX-1 inhibition). The reported rates are not only assay specific but also condition specific, with particularly high rates (up to 70%) previously reported in the stroke population. We investigated whether pharmacological responses to aspirin can be reliably determined from a functional test of AA-induced whole-blood clotting. A prospective study included 35 patients admitted with ischemic stroke and commenced on 300mg aspirin. AA-induced whole-blood clotting was measured using short thrombelastography, a previously extensively validated near-patient PFT. Serum TXB2 and inflammatory biomarkers were also measured. The prevalence of apparent aspirin resistance measured using AA was high (range from 49% to 67%). However, serum [TXB2] was consistently low, thereby confirming adequate inhibition of COX-1 by aspirin. Mean inflammatory biomarker levels were elevated throughout. This study demonstrates that although COX-1 activity is adequately and consistently suppressed by aspirin in stroke patients, this effect isnot reliably indicated by whole-blood clotting in response to AA. These data help to explain why the reported prevalence of aspirin resistance in stroke from studies employing AA-induced platelet reactivity is high and cast doubt on the veracity of such reports.

A Randomized Crossover Study Comparing the Antiplatelet Effect of Plavix Versus Generic Clopidogrel

Clopidogrel exists in different salt formulations. All published data that have demonstrated its beneficial effect are based entirely on the hydrogen sulphate salt contained in the branded product Plavix, which had US sales of $6.1 billion in 2010 alone. A number of cheaper generic versions of clopidogrel are increasingly being used in Europe as an alternative to Plavix, mainly for cost reasons. However, there is insufficient evidence to show that their pharmacodynamic effect is equivalent to Plavix. This prospective study investigated whether there is any significant difference in the antiplatelet effect of Plavix versus generic clopidogrel hydrochloride in healthy male volunteers. All participants received loading and maintenance doses of both drugs, in a crossover manner, separated by a 2-week washout period. Adenosine diphosphate (ADP)-induced platelet reactivity was measured using short thrombelastography at multiple timepoints. The results showed interindividual heterogeneity in responses to clopidogrel but no significant difference in ADP-induced platelet reactivity between Plavix versus generic clopidogrel hydrochloride. Our findings suggest comparable inhibition of ADP-induced platelet reactivity with Plavix and generic clopidogrel hydrochloride. This observation is particularly pertinent at a time when the patent for Plavix is expected to expire in the near future leading to the large-scale switch to cheaper generic preparations.

Personalised antiplatelet therapy in stent thrombosis: observations from the Clopidogrel Resistance in Stent Thrombosis (CREST) registry

ObjectivePrevious studies have demonstrated significant heterogeneity in responses to antiplatelet therapy (APT), and high residual platelet reactivity is associated with the risk of ischaemic events, including stent thrombosis (ST). The...

20 What happens to platelet function and vascular inflammation when clopidogrel is withdrawn? Insights using short thrombelastography

Introduction A clustering of adverse events, in particular stent thrombosis (ST) has been observed following clopidogrel cessation 1-year after drug-eluting stenting (DES), the aetiology of which is poorly understood. We investigated the effect of withdrawing clopidogrel in DES patients using a simple, rapid, reproducible near-patient platelet function test known as short Thrombelastography (s-TEG) that has been developed and validated by this group. Methods 33 patients on aspirin and due to stop clopidogrel at 1 year following DES were investigated. Venesection was performed at (i) 4 weeks and 24 h pre clopidogrel cessation (ii) 24 h, 48 h, 1, 2 and 4 weeks post clopidogrel cessation. At all time-points, platelet reactivity was determined using s-TEG and thromboxane (TX) B2, IL-6, CD40 ligand and high sensitivity CRP were measured. Results Clopidogrel cessation produced (i) a predictable increase in ADP-induced platelet aggregation, and (ii) an unexpected and significant rise in AA-induced platelet aggregation. TXB2 was consistently suppressed confirming inhibition of COX by aspirin. Conclusion We have described for the first time an aspirin-independent increase in AA-induced clotting following clopidogrel withdrawal in DES patients. As well as potentially helping to explain the observed clustering of ST events early after clopidogrel withdrawal, these findings raise the question as to whether AA-induced clotting is an appropriate test of aspirin sensitivity. Our results also confirm s-TEG as a plausible candidate for near-patient platelet function testing in this field.

Erratum

Cardiovascular TherapeuticsVolume 28, Issue 4 p. 254-254 Free Access Erratum This article corrects the following: Individualised Assessment of Response to Clopidogrel in Patients Presenting with Acute Coronary Syndromes: A Role for Short Thrombelastography? J.M. Cotton, A.M. Worrall, A.R. Hobson, A. Smallwood, V. Amoah, S. Dunmore, A.M. Nevill, R. Rajendra, J. Vickers, N. Curzen, Volume 28Issue 3Cardiovascular Therapeutics pages: 139-146 First Published online: April 19, 2010 First published: 05 July 2010 https://doi.org/10.1111/j.1755-5922.2010.00215.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat In [1], the name of the eighth author is currently listed incorrectly in the author list as R. Rajendra. The correct name is R. P. Raghuraman. The correct list of author names is below. J.M. Cotton, A.M. Worrall, A.R. Hobson, A. Smallwood, V. Amoah, S. Dunmore, A.M. Nevill, R.P. Raghuraman, J. Vickers, N. Curzen Reference 1 Cotton JM, Worrall AM, Hobson AR, et al. Individualised Assessment of Response to Clopidogrel in Patients Presenting with Acute Coronary Syndromes: A Role for Short Thrombelastography?. Cardiovasc Ther 2010; 28: 139– 146. Volume28, Issue4August 2010Pages 254-254 ReferencesRelatedInformation

Individualised Assessment of Response to Clopidogrel in Patients Presenting with Acute Coronary Syndromes: A Role for Short Thrombelastography?

There is considerable interindividual variation in response to the antiplatelet agent clopidogrel. Hyporesponse predicts negative outcomes in patients presenting with a variety of ischemic cardiac conditions and following intracoronary stent placement. Many tests of clopidogrel activity are time consuming and complex. Short thromboelastography (s-TEG) allows rapid measurement of platelet clopidogrel response. We initiated this study to investigate the utility of s-TEG in assessing the response to clopidogrel in patients presenting with acute coronary syndromes (ACS) and to compare these results with established clopidogrel monitoring techniques. Patients admitted with unstable angina (UA) or Non ST elevation myocardial infarction (NSTEMI) undergoing coronary angiography were recruited. After routine loading with clopidogrel, all patients were tested with s-TEG and Accumetrics Verify-Now rapid platelet function analyzer (VN-RPFA). We used the modified TEG technique of measuring area under the curve at 15 min (AUC15), which allows a rapid estimation of antiplatelet response. Vasodilator-stimulated phosphoprotein phosphorylation (VASP) was also tested in a subgroup of patients. Clinical follow-up was obtained at 1 year. s-TEG results were correlated with VN-RPFA and VASP findings. A total of 49 patients (33 male, mean age 63) were recruited and tested with s-TEG and VN-RPFA and a total of 39 patients were also assessed with VASP. s-TEG readings correlated well with VN-RPFA (r(2)= 0.54, P < 0.0001) and VASP (r(2)= 0.26, P= 0.001). s-TEG provides timely results which compare to current tests of clopidogrel activity. This technique can also be used to measure a variety of other clotting parameters and as such could develop into a valuable near patient test for the interventional cardiologist.

Gender and Responses to Aspirin and Clopidogrel: Insights Using Short Thrombelastography

There is significant variability in both baseline clotting tendency and response to antiplatelet therapy. Responses are associated with outcome. We have investigated whether differences could explain the increased risk observed in women presenting with coronary artery disease. We have utilized short thrombelastography to assess (i) baseline clotting responses, (ii) response to aspirin and clopidogrel, and (iii) post-treatment platelet reactivity in 48 young volunteers, 22 older patients and 18 patients with previous stent thrombosis. Baseline responses were significantly higher in young women than in men. While there was no difference in response to aspirin, platelet reactivity on aspirin remained higher in women (area under curve at 15 min [AUC15] of arachidonic acid channel 332 +/- 122 vs. 172 +/- 80, P= 0.04). Young women had less response to clopidogrel (% reduction in AUC15 with adenosine diphosphate [ADP] 36.4 +/- 12.4 vs. 64.0 +/- 13.2, P < 0.01) in addition to higher post-treatment reactivity (AUC15 of ADP 714 +/- 161 vs. 311 +/- 146, P < 0.01) compared to men. There were no such differences between male and female patients over 50. However, young women with previous stent thrombosis had among the highest platelet reactivity observed. Compared to men, young women have greater baseline clotting tendency, reduced response to clopidogrel, and greater post-treatment reactivity while on both aspirin and clopidogrel. Differences in clotting tendency and response to antiplatelet therapy may contribute to the excess risk observed in young women but are not observed in older female patients.

The Potential Value of Near Patient Platelet Function Testing in PCI: Randomised Comparison of 600 mg versus 900 mg Clopidogrel Loading Doses

Whilst poor response to clopidogrel is associated with adverse outcomes uncertainty exists as to how (a) response should be assessed and (b) poor responders managed. We utilised VerifyNow P2Y12 and short Thrombelastography (TEG) to assess 900 mg doses in (i) initial poor responders to 600 mg and (ii) in a randomised comparison with 600 mg. Blood was taken before and six hours post clopidogrel in (i) 30 volunteers receiving 600 mg (poor responders received 900 mg > two weeks later) and (ii) 60 patients randomized 1 : 1 to 600 mg or 900 mg doses. Poor response was defined as TEG %Clotting Inhibition (%CIn) or VerifyNow Platelet Response Unit (PRU) reduction <30%. (i) Poor responders to 600 mg had greater PRU reduction (45.0 versus 20.1%, P = 0.03) and greater %CIn (22.9 versus −15.1%, P = 0.01) after 900 mg but (ii) there were no significant differences between the patient groups. Near-patient assessment of response to clopidogrel is feasible and clinically useful. Whilst ineffective on a population basis 900 mg doses increase the effect of clopidogrel in initial poor responders.