Daniel I. Simon, M.D. Associate Director, Interventional Cardiology Brigham and Women’s Hospital Associate Professor of Medicine Harvard Medical School Boston, MA USA ASA Resistance and Clinical Outcomes

ASA Resistance: Key Questions Does a standardized definition exist? Are there reliable tests to diagnose this phenomenon? What are the possible mechanisms and future implications? Does it have any clinical significance? How do we manage patients with Aspirin resistance?

Established Platelet Function Tests Harrison P. Br J Hematology 2000;111: Platelet Function Test Bleeding time Aggregometry-turbidometric methods Aggregometry-impedance methods Aggregometry & luminescence Adenine nucleotides Thromboelastography (TEG) Glass filterometer Platelet release markers In Vivo screening test Responsiveness to panel agonists Combined aggregation and ADP release Stored and released ADP Global Hemostasis High shear platelet function In vivo platelet activation markers Advantages Physiological Diagnostic Whole blood test More information Sensitive Predicts bleeding Simple Simple, systemic measure of platelet activation Disadvantages Insensitive, invasive & high variability Labor intensive & non- physiological Insensitive Semi-quantitative Specialized equipment Measures clot properties only, insensitive to ASA Requires blood counter Prone to artifact Plt Function Test DisadvantagesAdvantagesAssay

Newer Platelet Function Tests (PFA)-100 Whole blood + Primary Limited range-most pts hemostasis after GP IIb/IIIa inhibitors have (high shear closure times >300 sec, so may adhes/aggreg) not be able to discern diff. Used to assay ADP antagonist Clot Signature Whole blood + Adhesion, Large instrument for routine use Analyzeraggregation and interpretation of results is complex Rapid platelet Whole blood + Aggregation GP IIb/IIa: baseline sample req. function assay Clinical outcome data (GOLD) Aspirin: AA-like agonist Harrison P. Br J Hematology 2000;111: Mukherjee D & Moliterno DJ. Clin Pharmacokinet 2000;39(6): Flow cytometry Whole blood - Platelet GP, Flexible & powerful. Requires activation markers, specialized operator. Expensive Platelet function AssaySubstrate BedsidePrincipleComments

Prevalence of ASA Resistance Gum PA et al. Am J Cardiol 2001;88: ASA-R: mean aggregation ≥70% with µM 10 ADP & ≥20% with 0.5 mg/ml AA 325 patients with stable CVD taking ASA 325 mg >7days

Wang JC et al. Amer J Cardiol 2003;92: patients presenting to cardiac cath lab on ASA mg >7d Prevalence of Aspirin Resistance 23.4% Aspirin non-responsive Accumetrics VerifyNow Aspirin Definition: ARU > 550 Multivariate analysis: history of CAD associated with twice the odds of being ASA non-responder (odds ratio 2.09, 95% CI , p=0.009) No association with gender, DM, smoking, ASA dose

Clinical Studies

ASA Resistance: Long-term Clinical Studies Stroke mg Plt Reactivity 24 mStroke/MI/ 10-fold lower (n=180) Vascular death risk in ASA responders PVD mg Whole blood 18 m Arterial 87% higher r isk (n=100) aggregometry Occlusion in ASA-R CVD/CVA mg PFA-10>60 mRecurrent CVA/ Recurrent CVA 34% (n=53) TIA TIA ASA-R vs. 0% no recurrent events Subgroup mg Urinary 11-dehydro 5 yrs MI/Stroke/ 1.8 times HOPE 4 TX B2 CVDeath higher risk in (n=967) upper vs. lower quartile CVD mg Optical platelet 679±185 Death/MI/CVA 24% ASA-R vs. (n=326) aggregation days 10% ASA-S [HR 3.12 (95% CI , p=0.03) 1.Grotemeyer KH, et al. Thromb Res 1993; 71: Mueller MR, et al. Thromb Haemost 1997; 78: Grundmann K, et al. J Neurol 2003; 250: Eikelboom JW, et al. Circulation 2002; 105: Gum PA, et al. J Am Coll Cardiol 2003; 41: PtsASA doseTestF/UEnd-pointResults

ASA Resistance and Clinical Outcome in CAD Patients Eikelboom JW, et al. Circulation 2002; 105: HOPE Trial Substudy: ASA mg

ASA Resistance and Clinical Outcome in CVD Patients Gum PA, et al. J Am Coll Cardiol 2003; 41: ASA-R: mean aggregation ≥70% with 10 µM ADP & ≥20% with 0.5 mg/ml AA 326 CVD patients on ASA 325 mg > 7 days p=0.03

ASA Resistance and Clinical Outcome in PVD Patients Mueller MR et al. Thromb Haemost 1997; 78:

ASA Resistance and Clinical Outcome in Stroke Patients Grotemeyer KH et al. Thromb Res 1993; 71:

ASA Resistance and Clinical Outcome in Stroke Patients Grundmann K et al. J Neurol 2003; 250: CVA pts on ASA 100 mg for secondary prevention > 60 months

Chen et al. J Amer Coll Cardiol 2004;43: ASA Resistance in PCI RPFA-ASA, ASA/clopidogrel (n=151), 19.2% ASA resistant

Oral Antiplatelet Agents Collagen Thrombin TXA 2 Aspirin ADP (FibrinogenReceptor) clopidogrel bisulfate TXA 2 ADP Dipyridamole Phosphodiesterase ADP Gp IIb/IIIa Activation COX ticlopidine HCl ADP = adenosine diphosphate, TXA2 = thromboxane A2, COX = cyclooxygenase. Schafer AI. Am J Med 1996;101:199–209.

Clopidogrel in Unstable Angina to Prevent Recurrent Ischemic Events The CURE Trial Investigators. N Engl J Med. 2001;345: Aspirin mg Placebo Clopidogrel300mg loading dose Patients with Non-ST elevation Acute Coronary Syndrome R Months Months 3 months  double-blind treatment  12 months Clopidogrel 75mg q.d. + ASA mg q.d.* (6259 patients) Placebo + ASA mg q.d.* (6303 patients)

* In combination with standard therapy The CURE Trial Investigators. N Engl J Med. 2001;345: Cumulative Hazard Rate Clopidogrel + ASA* 369 Placebo + ASA* Months of Follow-Up 11.4% 9.3% 20% RRR P < N = 12, Primary Endpoint: MI/Stroke/CV Death

PCI PLACEBO + ASA * + ASA * CLOPIDOGREL 300 mg 3-24h pre-PCI + ASA * 30 days post PCI End of follow-up Up to 12 months after randomization Clopidogrel 75 QD Pretreatment Pretreatment N = 2,116 patients undergoing elective PCI * In combination with standard therapy N = 1345 N = 1313 R CREDO

Steinhubl et al. JAMA 2002 CREDO: Primary Endpoint 26.9% relative risk reduction (CI %; P=0.02) Absolute reduction = 3%

Aspirin Resistant Patient Management Eliminate interfering substances (ibuprofen) Increase aspirin dose Use other anti-platelet medications such as clopidogrel to prevent recurrent ischemic events Educate patient on importance of compliance

Conclusions ASA use associated with 23% reduction in the odds of vascular events Beneficial anti-thrombotic effect of ASA mediated by irreversible acetylation of COX-1 ASA resistance 5-60% ASA resistance associated with increased risk of major adverse cardiovascular events