Research Article

The effect of enoxaparin on in vitro stimulated platelet aggregation by elective percutaneous coronary intervention patients


  • Ebru İpek Türkoğlu
  • Nazan Bitir

Received Date: 11.02.2017 Accepted Date: 17.05.2017 EJCM 2017;5(2):21-26


The aim of the present study was to investigate the effects of enoxaparin on in vitro stimulated platelet aggregation by elective percutaneous coronary intervention patients.


Twenty-two patients that scheduled for elective percutaneous coronary angioplasty (PTCA) were enrolled in the present study. The patients who had not been taking any antiaggregant agent other than aspirin and normal platelet account received enoxaparin (1mg/kg IV bolus) as anticoagulant agent during PTCA. Two blood samples were obtained for every patient via femoral arterial sheath during the intervention before and 10 minutes after enoxaparin administration and stimulated platelet aggregation responses are investigated.


The decrease in platelet aggregation responses to adenosine diphosphate (ADP), collagen and epinephrine before and after enoxaparin administration were statistically significant (p<0.05). The decrease in platelet aggregation response to ristocetin before and after enoxaparin was not statistically significant (p>0.05).


Enoxaparin may reduce platelet aggregation in elective PTCA patients pretreated with aspirin only. With the knowledge of the importance of the platelet inhibition, choice of the anticoagulant agent during PTCA may be beneficial.

Keywords: Enoxaparin, stimulated platelet aggregation, elective PTCA


Subcutaneous (SC) enoxaparin has been shown to be better choice than unfractionated heparin (UFH) in the medical treatment of unstable angina (UA) and non-ST- elevation myocardial infarction (NSTEMI).(1-4) Combined analysis of two studies, the Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events (ESSENCE) and Thrombolysis In Myocardial Infarction (TIMI) 11B, showed that enoxaparin reduced the risk of death and MI by 20% at 43 days without any significant increase of major hemorrhage.(5) ESSENCE and TIMI 11B trials demonstrated superiority of enoxaparin over UFH at 43 days for end points death or myocardial infarction (MI) and death or MI or urgent revascularization in patients who did not undergo percutaneous coronary intervention (PCI).(5)

In this analysis, excluding events that occurred before PCI, there was also superiority of enoxaparin treatment over UFH measured at 1 year for both end points in patients who underwent PCI.(5) Several studies have shown good outcomes with SC enoxaparin anticoagulation of patients with UA/NSTEMI underwent PCI on SC enoxaparin treatment.(6-8) Intravenous (IV) low-molecular-weight heparins (LMWH) in elective PCI have been evaluated and shown to be safe and effective in various registries.(3,9-11)

There are several studies that measure platelet reactivity in stable PCI patients using different methods.(12-14) The aim of the present study was to investigate the effect of enoxaparin on in vitro stimulated platelet aggregation by using % aggregation test to certain agonists in elective coronary intervention patients and the clinical significance of aggregation response to enoxaparin.

Materials and Methods

Study Population

Study population comprised patients older than 30 years with stable angina pectoris and documented ischemia (positive treadmill exercise test or positive myocardial perfusion scan for ischemia), who underwent coronary angiography and scheduled for elective PCI.

Exclusion criteria were: 

  1. unstable state or acute coronary syndrome,
  2. stable angina with an identified precipitating factor (e.g. severe anemia, heart failure, tachyarrhythmia, thyrotoxicosis, severe uncontrolled hypertension),
  3. myocardial infarction or PCI in previous month or coronary bypass surgery in 2 months,
  4. treatment with UFH or LMWH >24 hours of any cause before enrollment,
  5. treatment with any other anti-platelet agent than aspirin (e.g. clopidogrel, ticlopidin, dipridamol),
  6. refusal of patient

22 patients, 16 males and 6 females were enrolled to the study. Mean age was 56.8 ± 1.6 years. Mean age for female patients was 57.4 ± 2.1 and for male patients 56.7 ± 1.4. Seventeen patients (14 of males and 3 of females) were smoker.  Only 3 patients (2 of males and 1 of females) had diabetes mellitus and none were under insulin treatment. Fifteen patients (11 of males and 4 of females) had hypertension and were under treatment. Seventeen patients (12 of males and 5 of females) were under statin treatment since their coronary angiography procedures.

Concomitant medication was similar in male and female patients. All of patients received daily aspirin (ASA) > 100 mg more than 7 days before procedure. Fifteen of males and 5 of females were taking beta-blockers. Fourteen of males and 5 of females were using nitrates. All hypertensive patients were taking ACE-inhibitors and all of hyperlipidemic patients were taking statins.

Blood Collection

Immediately after femoral sheath replacement the first blood sample was drawn through the sheath to determine the basal (before anticoagulant) platelet aggregation response. Enoxaparin was given 1 mg/kg (100IU/kg) IV bolus after PTCA-wire crossed the lesion as a single dose. Ten minutes after the administration of enoxaparin the second blood sample was drawn through the sheath.

In vitro Platelet Aggregation Measurement

Immediately after blood collection, platelet aggregation measurements were made. All blood samples were studied into 2 hours after their collection. In vitro platelet functions were evaluated in the hematology laboratory with agregometer.  Stimuli were adenosine diphosphate (ADP), collagen, epinephrine and ristocetin. PAP-4CD Bio-Data was used for platelet aggregation.

Statistical Analysis

A student-paired t-test was applied to assess the differences between pre- and post-enoxaparin platelet aggregation responses. Results are expressed as mean ± standard error (SE). The level of significance was set at p <0.05.  SPSS 10.0 software was used for the statistical analysis.

The alteration in the platelet aggregation response with certain stimuli before and after enoxaparin is investigated in order to explore if enoxaparin has an additional antiaggregant effect.


Baseline clinical characteristics of study population and concomitant medications are described in Table 1 and 2. Baseline platelet counts were within normal limits in the study population and were unchanged after the intravenous administration of enoxaparin (212 ± 48×106 before and 210 ± 42×106 after enoxaparin). Not any major bleeding complication occurred. None of patients had required blood transfusion. Only 3 of patients had small hematoma on the femoral access site. In this study not any in-hospital complication (such as ischemic complications or infection) was experienced.

Stimulated platelet aggregation responses before and after enoxaparin are summarized in Table 3. Values are given as mean ± SE of % aggregation. Platelet aggregation responses to ADP were 36.2 ± 4.6 before and 29.3 ± 3.4 after enoxaparin (p=0.005) and to epinephrine 41.4 ± 5.3 before and 30.5 ± 4.7 after enoxaparin (p=0.02). The difference was statistically significant. Platelet aggregation responses to collagen were 57.8 ± 5.0 before and 45.7 ± 6.0 after enoxaparin (p=0.05); to ristocetin 75.0 ± 3.0 before and 67.0 ± 4.3 after enoxaparin (p=0.07).


Despite of new tools, new drugs and new techniques, clot formation remains still as an important issue in interventional cardiology. The UFH has been the primary anticoagulant agent for more than 30 years, but the optimal dosage, the monitoring of anticoagulation level and the interaction between UFH and platelets remain controversial.(15-17) LMWHs offer a stable and predictable anticoagulant response and do not need for coagulation monitoring.(18) Enoxaparin has shown its superiority to UFH in the medical treatment of UA and NSTEMI.(1,2) There is also a meta-analysis revealing a better evolution in ST-segment elevation acute myocardial infarction patients, who received enoxaparin instead of UFH as an adjunctive therapy to the thrombolytic regimen.(4) Several studies have also shown good results with enoxaparin on UA/NSTEMI patients who underwent PCI.(6-8)

There are some potential mechanisms, which may explain beneficial effects of enoxaparin.(18) Because of the molecular features enoxaparin may permit more suppression of thrombin generation than UFH with a higher antifactor Xa: antifactor IIa (thrombin) ratio (3.8:1).(18) Enoxaparin has a prolonged antifactor Xa activity and higher antifactor IIa activity than UFH because of better bioavailability, is less sensitive to the inhibitory effects of platelet factor 4, may release the tissue factor pathway inhibitor with greater capacity, has a lower tendency to increase activation and aggregation of platelets and shows potential antiplatelet effects while suppressing von Willebrand factor greater degree.(18,19-28)

The aim of this study was to investigate the aggregation response of stable patients to enoxaparin via platelet functions beyond its anticoagulation activity. To the best our knowledge, this is the first study that compared parameters of platelet aggregation before and after administration of enoxaparin during elective PCI in patients pretreated only with aspirin. All unstable patients were excluded to avoid the interaction between activated aggregation and coagulation cascade and platelet aggregation response. In the present study, enoxaparin showed a slight decrease of % aggregation on platelet aggregation responses stimulated with collagen and ristocetin but it was statistically not significant. Enoxaparin significantly decreased platelet aggregation responses stimulated with ADP and with epinephrine in elective PCI patients. None of our patients experienced any ischemic or hemorrhagic complications neither in 72 hours nor in 30 days in follow-up.

Platelets play a key role in the development of thrombotic events during and after PCI.(29-31) There are multiple pathways of platelet activation and aggregation. Thrombin is the most potent agent, which activates platelets in subnanomolar concentrations via protease-activated receptors (PARs).(31,32,33) PAR activation results ADP release from dense granules, which acts in an autocrine way on the platelet ADP receptors.(31,34)

This endogenous ADP release may be reduced via enoxaparin resulting in significant decrease of ADP induced platelet aggregation. In a previous study Xiao et al. investigated platelet aggregation response to enoxaparin in patients taking only aspirin with UA and found a modest but not statistically significant increase in platelet aggregation with enoxaparin.(25) The conflict may be related to the study population. While UA patients have been included to the study of Xiao et al, all UA patients were excluded from the present study.(25) In another study, Aggarwal et al. have found that anticoagulation with enoxaparin during hemodialysis is associated with less platelet reactivity in a different study population.(35)

The limitations of the present study were small number of patients and lack of unstable patients. In acute coronary syndromes and unstable patients, especially by the site of thrombus, antiaggregant effect of enoxaparin may be more critical, but further studies are needed. In conclusion, enoxaparin may reduce platelet aggregation in elective PCI patients treated with aspirin only. With the knowledge of the stronger the platelet inhibition, the lower the incidence of ischemic complications,(36-39)choice of the anticoagulant agent or additional antiaggregant agents during PCI may be beneficial.

Ethical approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.


We wish to thank to the Ege University, divison of Hematology.


  1. Antman EM, McCabe CH, Gurfinkel EP, Turpie AG, Bernink PJ, Salein D, Bayes de Luna A, Fox K, Lablanche JM, Radley D, Premmereur J, Braunwald E. Enoxaparin prevents death and cardiac ischemic events in unstable angina/non-Q-wave myocardial infarction (TIMI) 11B trial. Circulation 1999; 100: 1593-601
  2. Goodman SG, Cohen M, Bigonzi F, Gurfinkel EP, Radley DR, Le Iouer V, Fromell GJ, Demers C, Turpie AG, Califf RM, Fox KA, Langer A. Randomized trial of low molecular weight heparin (enoxaparin) versus unfractionated heparin for unstable coronary artery disease: 1-year results of the ESSENCE Study. Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events. J Am Coll Cardiol 2000; 36: 693-8
  3. Choussat R, Montalescot G, Collet JP, Vicaut E, Ankri A, Gallois V, Drobinski G, Sotirov I, Thpmas D. A unique, low dose of intravenous enoxaparin in elective percutaneous coronary intervention. J Am Coll Cardiol 2002; 40: 1943-50
  4. Theroux P, Welsh RC. Meta-analysis of randomized trials comparing enoxaparin versus unfractionated heparin as adjunctive therapy to fibrinolysis in ST- elevation acute myocardial infarction. Am J Cardiol 2003; 91: 860-4
  5. Fox KA, Antman EM, Cohen M, Bigonzi F; ESSENCE/TIMI11B Investigators. Comparison of enoxaparin versus unfractionated heparin in patients with unstable angina pectoris / non-ST segment elevation acute myocardial infarction having subsequent percutaneous coronary intervention. Am J Cardiol 2002; 90: 477-82
  6. Collet JP, Montalescot G, Lison L, Choussat R, Ankri A, Drobinski G, Sotirov I, Thomas D. Percutaneous coronary intervention after subcutaneous enoxaparin pretreatment in patients with unstable angina pectoris. Circulation 2001; 103: 658-63
  7. Fergusson JJ, Antman EM, Bates ER, Cohen M, Every NR, Harrington RA, Pepine CJ, Theroux P; NICE Investigators. The use of enoxaparin and IIb/IIIa antagonists in acute coronary syndromes, including PCI: final results of NICE 3 study (abstr). J Am Coll Cardiol 2001; 37: 365A
  8. Goodman SG, Fitchett D, Armstrong PW, Tan M, Langer A; INTERACT Trial Investigators. The Integrilin and Enoxaparin Randomized Assessment of Acute Coronary syndrome Treatment (INTERACT) trial (abstr). J am Coll Cardiol 2002; 405: 5
  9. Rabah MM, Premmereur J, Graham M, Fareed J, Hoppensteadt DA, Grines LL, Grines CL. Usefulness of intravenous enoxaparin for percutaneous coronary intervention in stable angina pectoris. Am J Cardiol 1999; 84: 1391-5
  10. Kereiakes DJ, Kleiman NS, Fry E, Mwawasi G, Lengerich R, Maresh K, Burkert ML, Aquilina JW, DeLoof M, Broderick T, Shimshak TM. Dalteparin in combination with abciximab during percutaneous coronary intervention. AM Heart J 2001; 141: 348-52
  11. Kereiakes DJ, Grines C, Fry E, Esente P, Hoppensteadt D, Midei M, Barr L, Matthai W, Todd M, Broderick T, Rubinstein R, Fareed J, Santoian E, Neidarman A, Brodie B, Zidar J, Ferguson JJ, Cohen M; NICE 1 and NICE 4 Investigators. Enoxaparin and abciximab adjunctive pharmacotherapy during percutaneous coronary intervention. J Invasive Cardiol 2001; 13: 272-8
  12. Kabbani SS, Watkins MW, Ashikaga T, Terrien EF, Holoch PA, Sobel BE, Schneider DJ. Platelet reactivity characterized prospectively: a determinant of outcome 90 days after percutaneous coronary intervention. Circulation 2001; 104: 181-6
  13. Kabbani SS, Watkins MW, Holoch PA, Terrien EF, Sobel BE, Schneider DJ. Platelet reactivity in coronary ostial blood: a reflection of the thrombotic state accompanying plaque rupture and J Thromb Thrombolysis 2001; 12: 171-6
  14. Aggarwal A, Sobel BE, Schneider DJ. Decreased platelet reactivity in blood anticoagulated with bivalirudin or enoxaparin compared with unfractionated heparin: implications for coronary intervention. J Thromb Thrombolysis 2002; 13: 161-6
  15. Eika C. Inhibition of thrombin-induced aggregation of human platelets in heparin. Scand J Haematol 1971; 8: 216-222.
  16. Thomson C, Forbes CD, Prentice CRM. The potentiation of platelet aggregation and adhesion by heparin in vitro and in vivo. Clin Sci Mol Med 1973; 45: 485 – 494
  17. Mascelli MA, Kleiman N, Marciniak S, Damaraju L, Weisman HF, Jordan RE. Therapeutic heparin concentrations augment platelet reactivity: Implications for the pharmacologic assessment of the glycoprotein IIb/IIIa antagonist abciximab. Am Heart J 2000; 139: 696-703.
  18. Antman EM, Cohen M, McCabe C, Goodman SG, Murphy SA, Braunwald E; TIMI 11 B and ESSENCE Investigators. Enoxaparin is superior to unfractionated heparin for preventing clinical events at 1-year follow-up of TIMI 11B and ESSENCE. Eur Heart J 2002; 23: 308-14
  19. Lane DA, Denton J, Flynn AM, Thunberg L, Lindahl U. Anticoagulant activities of heparin oligosaccharides and their neutralization by platelet factor 4. Biochem J 1984; 218: 725-32
  20. Abildgaard U, Lindahl AK, Sandset PM. Heparin requires both antithrombin and extrinsic pathway inhibitor for its anticoagulant effect in human blood. Haemostasis 1991; 21: 254-7
  21. Lindhout T, Hemker H. Anticoagulant mechanism of action of low molecular weight heparins. In: Doutremepuich C. ed. Low Moleculer Weight Heparins in Clinical Practice. New York: Marcel Dekker, Inc. 1992: 23-50
  22. Hoppensteadt DA, Jeske W, Fareed J, Bermes EW Jr. The role of tissue factor pathway inhibitor in the mediation of the antithrombotic actions of heparin and low molecular weight heparin. Blood Coagul Fibrinolysis 1995; 6 (Suppl): S57-64
  23. Brieger D, Daves J. Long-term persistence of biological activity following administration of Enoxaparin sodium (clexane) is due to sequestration of antithrombin-binding low molecular weight fragments- comparison with unfractionated heparin. Thromb Haemost 1996; 75: 740-6
  24. Agnelli G. Pharmacological activities of heparin chains: should our past knowledge be revised? Haemostasis 1996; 26:2-9
  25. Xiao Z, Threoux P. Platelet activation with unfractionated heparin at therapeutic concentrations and comparisons with a low molecular weight heparin and with a direct thrombin inhibitor. Circulation 1998; 97: 251-6
  26. Montalescot G, Philippe F, Ankri A, Vicaut E, Bearez E, Poulard JE, Carrie D, Flammang D, Dutoit A, Carayon A, Jardel C, Chevrot M, Bastard JP, Bigonzi F, Thomas D. Early increase of von Willebrand factor predicts adverse outcome in unstable coronary artery disease: beneficial effects of enoxaparin. French Investigators of the ESSENCE Trial. Circulation 1998; 98: 294-9
  27. Antman EM, Handin R. Low molecular weight heparins: an intriguing new twist with profound implications. Circulation 1998; 98: 287-9
  28. Montalescot G, Collet JP, Lison L, Choussat R, Ankri A, Vicaut E, Perlemuter K, Philippe F, Drobinski G, Thomas D. Effects of various anticoagulant treatments on von Willebrand factor release in unstable angina. J Am Coll Cardiol 2000; 36:110-4
  29. Fuster V, Badimon L, Badimon JJ, Chesebro JH. The pathogenesis of coronary artery disease and acute coronary syndromes (1). N Engl J med 1992; 326: 242-50
  30. Massberg S, Schulz C, Gavaz M. Role of platelets in the pathophysiology of acute coronary syndrome. Semin Vasc Med 2003; 3: 147-62
  31. Sibbing D, Busch G, Braun S, Jawansky S, Schömig A, Kastrati A, Ott I, von Beckerath N. Impact of bivalirudin or unfractionated heparin on platelet aggregation in patients pretreated with 600 mg clopidogrel undergoing elective percutaneous coronary intervention. Eur Heart J 2008; 29: 1504-9
  32. Kahn ML, Nakanishi-Matsui M, Shapiro MJ, Ishihara H, Coughlin SR. Protease-activated receptors 1 and 4 mediate activation of human platelets by thrombin. J Clin Invest 1999; 103: 879-87
  33. Sambrano GR, Weiss EJ, Zheng YW, Huang W, Coughlin SR. Role of thrombin signaling in platelets in haemostasis and thrombosis. Nature 2001; 413: 74-8
  34. Dorsam RT, Kunapuli SP. Central role of the P2Y12 receptor in platelet activaton. J Clin İnvest 2004; 113: 340-45
  35. Aggarwal A, Whitaker DA, Rimmer JM, Solomon RJ, Gennari FJ, Sobel BE, Schneider DJ. Attenuation of platelet reactivity by enoxaparin compared with unfractionated heparin in patients undergoing haemodialysis. Nephrol Dial Transplant 2004; 19 (6): 1559-63
  36. Mehta SR, Yusuf S, Peters RJ, Bertrand ME, Lewis BS, Natarajan MK, Malmberg K, Rupprecht H, Zhao F, Chrolavicius S, Copland I, Fox KA; the CURE investigators. Effects of pretreatment with clopidogrel and aspirin followed by long-term therapy in patients undergoing percutaneous coronary intervention: the PCI-CURE study. Lancet 2001;358:527-33
  37. Patti G, Colonna G, Pasceri V, Pepe LL, Montinaro A, Di Sciascio G. Randomized trial of high loading dose of clopidogrel for reduction of periprocedural myocardial infarction in patients undergoing coronary intervention: results from the ARMYDA-2 study. Circulation 2005; 111:2099-106
  38. Wiviott SD, Braunwald E, McCabe CH, Montalescot G, Ruzyllo W, Gottlieb S, Neumann FJ, Ardissino D, DeServi S, Murphy SA, Riesmeyer J, Weerakkody G, Gibson M, Antman M; TRITON-TIMI 38 Investigators. Prasugrel versus clopidogrel in patients with acute coronary syndromes. N Engl J Med 2007; 357:2001-15
  39. Wallentin L, Becker RC, Budaj A, Cannon CP, Emanuelsson H, Held C, Horrow J, Husted S, James S, Katus H, Mahaffey KW, Scirica BM, Skene A, Steg PG, Storey RF, Harrington RA; PLATO Investigators. Ticagrelor versus clopidogrel in patients with acute coronary syndromes. N Eng J Med 2009; 361:1045-57.