Prior aspirin use predicts worse outcomes in patients with non-ST-elevation acute coronary syndromes. PURSUIT Investigators. Platelet IIb/IIIa in Unstable angina: Receptor Suppression Using Integrilin Therapy

Pre-admission antiplatelet therapy and treatment effect of ticagrelor vs. prasugrel in patients with acute coronary syndromes-a subgroup analysis of the ISAR-REACT 5 trial

AIMS

To assess whether the efficacy and safety of ticagrelor vs. prasugrel in patients with acute coronary syndromes (ACSs) are influenced by pre-admission treatment with aspirin and/or clopidogrel.

METHODS AND RESULTS

Patients (n = 4018) were categorized into two groups: pre-admission aspirin and/or clopidogrel group (n = 1455) and no pre-admission aspirin or clopidogrel group (n = 2563). The primary endpoint was the composite of all-cause death, myocardial infarction, or stroke; the secondary safety endpoint was Bleeding Academic Research Consortium (BARC) type 3-5 bleeding, both at 1 year. Patients in the pre-admission aspirin and/or clopidogrel group had a higher risk of ischaemic events, but a similar risk of bleeding to patients in the no pre-admission aspirin or clopidogrel group (cumulative incidences 10.5% vs. 6.7%, and 5.7% vs. 5.7%, respectively). The primary endpoint occurred in 81/717 patients assigned to ticagrelor and 69/738 patients assigned to prasugrel in the pre-admission aspirin and/or clopidogrel group [11.5% vs. 9.5%; hazard ratio (HR) = 1.23; 95% confidence interval (CI) 0.89-1.69], and in 103/1295 patients assigned to ticagrelor and 68/1268 patients assigned to prasugrel in the no pre-admission aspirin or clopidogrel group [8.0% vs. 5.4%; HR = 1.50 (1.10-2.03); Pint = 0.38]. BARC type 3-5 bleeding events did not differ between ticagrelor and prasugrel in patients in the pre-admission aspirin and/or clopidogrel (6.2% vs. 4.5%) or no pre-admission aspirin or clopidogrel (5.3% vs. 5.1%) group (Pint = 0.54).

CONCLUSION

In patients with ACS, pre-admission therapy with aspirin and/or clopidogrel has no influence on the relative efficacy and safety of ticagrelor and prasugrel.

Antiplatelet agents for chronic kidney disease

BACKGROUND

Antiplatelet agents are widely used to prevent cardiovascular events. The risks and benefits of antiplatelet agents may be different in people with chronic kidney disease (CKD) for whom occlusive atherosclerotic events are less prevalent, and bleeding hazards might be increased. This is an update of a review first published in 2013.

OBJECTIVES

To evaluate the benefits and harms of antiplatelet agents in people with any form of CKD, including those with CKD not receiving renal replacement therapy, patients receiving any form of dialysis, and kidney transplant recipients.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 13 July 2021 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We selected randomised controlled trials of any antiplatelet agents versus placebo or no treatment, or direct head-to-head antiplatelet agent studies in people with CKD. Studies were included if they enrolled participants with CKD, or included people in broader at-risk populations in which data for subgroups with CKD could be disaggregated.

DATA COLLECTION AND ANALYSIS

Four authors independently extracted data from primary study reports and any available supplementary information for study population, interventions, outcomes, and risks of bias. Risk ratios (RR) and 95% confidence intervals (CI) were calculated from numbers of events and numbers of participants at risk which were extracted from each included study. The reported RRs were extracted where crude event rates were not provided. Data were pooled using the random-effects model. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

MAIN RESULTS

We included 113 studies, enrolling 51,959 participants; 90 studies (40,597 CKD participants) compared an antiplatelet agent with placebo or no treatment, and 29 studies (11,805 CKD participants) directly compared one antiplatelet agent with another. Fifty-six new studies were added to this 2021 update. Seven studies originally excluded from the 2013 review were included, although they had a follow-up lower than two months. Random sequence generation and allocation concealment were at low risk of bias in 16 and 22 studies, respectively. Sixty-four studies reported low-risk methods for blinding of participants and investigators; outcome assessment was blinded in 41 studies. Forty-one studies were at low risk of attrition bias, 50 studies were at low risk of selective reporting bias, and 57 studies were at low risk of other potential sources of bias. Compared to placebo or no treatment, antiplatelet agents probably reduces myocardial infarction (18 studies, 15,289 participants: RR 0.88, 95% CI 0.79 to 0.99, I² = 0%; moderate certainty). Antiplatelet agents has uncertain effects on fatal or nonfatal stroke (12 studies, 10.382 participants: RR 1.01, 95% CI 0.64 to 1.59, I² = 37%; very low certainty) and may have little or no effect on death from any cause (35 studies, 18,241 participants: RR 0.94, 95 % CI 0.84 to 1.06, I² = 14%; low certainty). Antiplatelet therapy probably increases major bleeding in people with CKD and those treated with haemodialysis (HD) (29 studies, 16,194 participants: RR 1.35, 95% CI 1.10 to 1.65, I² = 12%; moderate certainty). In addition, antiplatelet therapy may increase minor bleeding in people with CKD and those treated with HD (21 studies, 13,218 participants: RR 1.55, 95% CI 1.27 to 1.90, I² = 58%; low certainty). Antiplatelet treatment may reduce early dialysis vascular access thrombosis (8 studies, 1525 participants) RR 0.52, 95% CI 0.38 to 0.70; low certainty). Antiplatelet agents may reduce doubling of serum creatinine in CKD (3 studies, 217 participants: RR 0.39, 95% CI 0.17 to 0.86, I² = 8%; low certainty). The treatment effects of antiplatelet agents on stroke, cardiovascular death, kidney failure, kidney transplant graft loss, transplant rejection, creatinine clearance, proteinuria, dialysis access failure, loss of primary unassisted patency, failure to attain suitability for dialysis, need of intervention and cardiovascular hospitalisation were uncertain. Limited data were available for direct head-to-head comparisons of antiplatelet drugs, including prasugrel, ticagrelor, different doses of clopidogrel, abciximab, defibrotide, sarpogrelate and beraprost.

AUTHORS' CONCLUSIONS

Antiplatelet agents probably reduced myocardial infarction and increased major bleeding, but do not appear to reduce all-cause and cardiovascular death among people with CKD and those treated with dialysis. The treatment effects of antiplatelet agents compared with each other are uncertain.

Impact of Antecedent Aspirin Use on Infarct Size, Bleeding and Composite Endpoint in Patients with de Novo Acute Myocardial Infarction

BACKGROUND

The study aimed to evaluate the impact of antecedent aspirin use on infarct size, bleeding and composite endpoint in patients with de novo acute myocardial infarction.

PATIENTS AND METHODS

A total of 562 consecutive patients with de novo acute myocardial infarction were included in this prospective cohort study. Patients were assigned into two groups based on presence (n=212) and absence (n=350) of prior aspirin use. Primary endpoint was myocardial infarct size, as estimated by troponin I peak. In-hospital mortality, bleeding and composite clinical endpoint including cardiogenic shock, stroke, in-hospital mortality and major bleeding were also evaluated.

RESULTS

Although GRACE and CRUSADE scores were higher, troponin I peak was lower in prior aspirin users. This result was maintained after adjustment for baseline ischemic risk profile and other major confounders including MI type and location. Despite high CRUSADE score, there was no increase in major and minor bleeding. Minimal bleeding was higher in antecedent aspirin users. When it was adjusted for the CRUSADE score, a similar risk was reported.

CONCLUSION

Patients with de novo acute myocardial infarction using aspirin for primary prevention have an unexpectedly smaller infarct size and similar bleeding rates.

Are Prior Aspirin Users With ST-Elevation Myocardial Infarction at Increased Risk of Adverse Events and Worse Angiographic Features?

Despite its clinical benefits, aspirin has been considered one of the predictors of worse outcomes in patients with unstable angina/non-ST-segment-elevation myocardial infarction. Nevertheless, such association has not been demonstrated in patients with ST-elevation myocardial infarction (STEMI). Five hundred eighty-six STEMI patients undergoing primary percutaneous coronary intervention were evaluated including 116 prior aspirin users. Angiographic characteristics and 1-year major adverse cardiac events (MACE) were then compared between the 2 groups. Adjusted analysis showed that the prior aspirin users had a significantly higher rate of totally occluded infarct-related artery before primary percutaneous coronary intervention (odds ratio: 1.859; P = 0.019). Postprocedural Thrombolysis in Myocardial Infarction flow grade 3 was less often demonstrated in the prior aspirin users (odds ratio: 1.512; P = 0.059). Aspirin consumption was associated with increased long-term mortality and MACE. Prior aspirin users had higher rate of MACE and worse pre- and postprocedural angiographic features. We suppose that patients who develop STEMI despite long-term aspirin intake probably reflect more vulnerable pre-existing coronary plaques with more thrombogenicity, which could negatively affect long-term cardiovascular outcomes.

Impact of Chronic Antiplatelet Therapy on Infarct Size and Bleeding in Patients With Acute Myocardial Infarction

BACKGROUND

Patients hospitalized with acute myocardial infarction (AMI) are often on prior single antiplatelet therapy (SAPT) or a dual antiplatelet therapy (DAPT). Whether chronic SAPT or DAPT is beneficial or associated with an increased risk in AMI is still controversial.

METHODS AND RESULTS

We prospectively enrolled 1718 consecutive patients with AMI (798 ST-segment elevation myocardial infarction and 920 non-ST-segment elevation myocardial infarction) who were divided according to their chronic APT (no APT, SAPT, or DAPT). The study primary end point was the infarct size, as estimated by troponin I peak. Incidence of major bleeding was also evaluated. Five hundred thirty-six (31%) patients were on chronic SAPT and 215 (13%) on DAPT. A graded increase in Global Registry of Acute Coronary Events (GRACE) and Can Rapid risk stratification of Unstable angina patients Suppress ADverse outcomes with Early implementation of the ACC/AHA guidelines (CRUSADE) risk scores was found going from patients without APT to those with DAPT, while a progressive smaller troponin I peak was observed with the increasing number of chronic antiplatelet agents (11.2 [interquartile range: 2-45] ng/mL, 6.6 [1-33] ng/mL, and 4.1 [1-24] ng/mL; P < .001 for trend). This result was maintained after adjustment for baseline ischemic risk profile (GRACE score) and other major confounders ( P < .001). The incidence of bleeding was higher in patients on chronic APT than in those without APT (5.2% vs 2.4%; P = .002). However, when the bleeding risk was adjusted for the CRUSADE risk score, chronic SAPT (odds ratio [OR]: 1.40, 95% confidence interval [CI]: 0.77-2.53) and DAPT (OR: 0.70, 95% CI: 0.29-1.70) were not associated with an increased bleeding risk.

CONCLUSION

In patients with AMI, chronic APT is associated with higher baseline ischemic and bleeding risks. Despite this and unexpectedly, they have a smaller infarct size and similar adjusted bleeding risk.

Prior chronic clopidogrel therapy is associated with increased adverse events and early stent thrombosis

Despite the growing use of clopidogrel, limited data exist regarding the prognostic significance of chronic clopidogrel therapy in patients sustaining acute coronary syndrome (ACS). Our aim was to determine whether patients sustaining ACS while on chronic clopidogrel therapy have a worse prognosis than clopidogrel-naïve patients. A total of 5,386 consecutive ACS patients were prospectively characterised and followed-up for 30 days. Of them, 680 (13 %) were treated with clopidogrel prior to the index ACS. Major adverse cardiovascular events (MACE) were defined as death, recurrent ACS, stroke and/or stent thrombosis. Compared with clopidogrel-naïve, chronic clopidogrel-treated patients were older (66 ± 12 vs 63 ± 13, respectively; p< 0.01), suffered more from diabetes mellitus, hypertension, dyslipidaemia, prior cardiovascular history, including prior myocardial infarction, revascularisation, coronary artery bypass graft and stroke (p< 0.01 for all), and were less likely to present with ST-elevation myocardial infarction (21 % vs 45 %; respectively; p < 0.001). Prior clopidogrel therapy was associated with a two-fold increase in in-hospital (1.6 °% vs 0.6, respectively; p =0.006) as well as 30-day stent thrombosis (2.2 % vs 1.0 %, respectively; p=0.007). MACE at 30 days was also higher among chronic clopidogrel-treated compared with clopidogrel-naïve patients [12.3 % vs 9.4 %, respectively; p< 0.01]. In multivariate log regression analysis chronic clopidogrel treatment was an independent predictor of stent thrombosis [OR=2.6 (95 %CI 1.2–5.6), p=0.001]. Patients sustaining ACS while on chronic clopidogrel treatment are at higher risk for in-hospital and 30-day adverse outcomes, including stent thrombosis.

Increased platelet aggregation and serum thromboxane levels in aspirin-treated patients with prior myocardial infarction

The antiplatelet effect of aspirin displays considerable inter-individual variability. We investigated the antiplatelet effect of aspirin in patients with coronary artery disease on aspirin mono-therapy with and without prior myocardial infarction (MI). Further, we investigated whether the effect of aspirin differed between patients with and without aspirin use at the time of MI onset. We performed a study on 231 patients, including 171 with prior MI. Among patients with only one prior MI (116 patients), 59 patients were on aspirin at the time of MI onset. All patients received 75 mg aspirin as mono-therapy. Platelet aggregation was assessed by multiple electrode aggregometry (Multiplate®) and Verify -Now®, and platelet activation was evaluated by soluble P-selectin. Furthermore, we measured serum thromboxane B2. MI patients had higher median platelet aggregation levels than patients without prior MI when evaluated by Multiplate® (parachidonic acid<0.0001, pcollagen=0.20). This was not supported by VerifyNow®. Furthermore, MI patients had higher median serum thromboxane B2 levels than patients without prior MI (p=0.01). Patients on aspirin before MI onset had significantly higher median aggregation levels compared with MI patients not on aspirin when evaluated by Multiplate® (pcollagen=0.02) and VerifyNow® (p<0.0001). In conclusion, patients with prior MI had higher platelet aggregation levels than patients without prior MI when evaluated by Multiplate®, despite same aspirin dose and optimal compliance. Serum thromboxane B2 levels were higher in MI patients than in patients without prior MI. Finally, patients on aspirin before MI onset had higher aggregation levels compared with patients not on aspirin.

Association Between Prior Aspirin Use and Morphological Features of Culprit Lesions at First Presentation of Acute Coronary Syndrome Assessed by Optical Coherence Tomography

BACKGROUND

The effect of prior use of aspirin (ASA) on the onset of acute coronary syndrome (ACS) has not been clarified. This study used optical coherence tomography (OCT) to investigate the morphological features of culprit lesions of ACS in patients with prior ASA use.Methods and Results:In total, 442 patients with their first ACS episode undergoing OCT for the culprit lesions were investigated. Clinical characteristics, OCT findings, and adverse events at 30 days were compared between patients with prior ASA use and ASA-naïve patients (non-ASA). 67 patients (15.2%) had received ASA at presentation. The ASA group was older, had higher frequency of dyslipidemia and hypertension, and lower renal function than the non-ASA group. Non-ST-elevation ACS was more prevalent in the ASA than in the non-ASA group (79.1 vs. 53.6%, P<0.001). Propensity score matching yielded 49 patients in both groups. OCT revealed less frequent thrombi in the ASA than in the non-ASA group in both the entire (37.3 vs. 75.2%, P<0.001) and score-matched cohorts (38.8 vs. 75.5%, P<0.001), whereas no significant difference was observed in plaque characteristics. Rate of adverse events did not differ between the ASA and the non-ASA groups in the matched cohort.

CONCLUSIONS

With a first ACS presentation, patients with prior ASA use were more likely to present with non-ST-elevation ACS with less frequent intraluminal thrombi, but no significant difference in underlying plaque characteristics or clinical course.

Impact of Prior Use of Four Preventive Medications on Outcomes in Patients Hospitalized for Acute Coronary Syndrome--Results from CPACS-2 Study

Background

It is widely reported that long-term use of four preventive medications (antiplatelet agents, angiotensin converting enzyme inhibitor / angiotensin receptor blocker, statin and beta-blockers) reduce the risk of subsequent acute coronary syndromes (ACS). It is unclear whether these four medications benefit patients who develop ACS despite its use.

Methods and Results

Logistic regression and propensity-score was applied among 14790 ACS patients to assess the association between prior use of four preventive medications and in-hospital outcomes including severity of disease at presentation (type of ACS, systolic blood pressure <90 mmHg, and heart rate> = 100 beats/min), complicating arrhythmia and major adverse cardiovascular events (MACEs, including all deaths, non-fatal myocardial infarction or re-infarction, and non-fatal stroke). Prior use of each of the four medications was significantly associated with less severity of disease (ORs ranged from 0.40 to 0.82, all P<0.05), less arrhythmia (ORs ranged from 0.45 to 0.64, all P<0.05), and reduced risk of MACEs (ORs ranged from 0.59 to 0.73, all P<0.05) during hospitalization. Multiple variable-adjusted ORs of MACEs were 0.77, 0.67, 0.48 and 0.59 respectively in patients with 1, 2, 3 and 4 medications in comparison with patients with none, and other clinical outcomes showed the same trend (P for trend < 0.05).

Conclusions

Among ACS patients in our study, those with prior use of four preventive medications presented with less disease severity, developed less arrhythmia and had a lower risk of in-hospital MACEs. The value of taking these medications may beyond just preventing occurrence of the disease.

Platelet glycoprotein IIb/IIIa blockers during percutaneous coronary intervention and as the initial medical treatment of non-ST segment elevation acute coronary syndromes

BACKGROUND

During percutaneous coronary intervention (PCI), and in non-ST segment elevation acute coronary syndromes (NSTEACS), the risk of acute vessel occlusion by thrombosis is high. Glycoprotein IIb/IIIa blockers strongly inhibit platelet aggregation and may prevent mortality and myocardial infarction. This is an update of a Cochrane review first published in 2001, and previously updated in 2007 and 2010.

OBJECTIVES

To assess the efficacy and safety effects of glycoprotein IIb/IIIa blockers when administered during PCI, and as initial medical treatment in patients with NSTEACS.

SEARCH METHODS

We updated the searches of the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 12, 2012), MEDLINE (OVID, 1946 to January Week 1 2013) and EMBASE (OVID, 1947 to Week 1 2013) on 11 January 2013.

SELECTION CRITERIA

Randomised controlled trials comparing intravenous IIb/IIIa blockers with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed trial quality and extracted data. We collected major bleeding as adverse effect information from the trials. We used odds ratios (OR) and 95% confidence intervals (CI) for effect measures.

MAIN RESULTS

Sixty trials involving 66,689 patients were included. During PCI (48 trials with 33,513 participants) glycoprotein IIb/IIIa blockers decreased all-cause mortality at 30 days (OR 0.79, 95% CI 0.64 to 0.97) but not at six months (OR 0.90, 95% CI 0.77 to 1.05). All-cause death or myocardial infarction was decreased both at 30 days (OR 0.66, 95% CI 0.60 to 0.72) and at six months (OR 0.75, 95% CI 0.64 to 0.86), although severe bleeding was increased (OR 1.39, 95% CI 1.21 to 1.61; absolute risk increase (ARI) 8.0 per 1000). The efficacy results were homogeneous for every endpoint according to the clinical condition of the patients, but were less marked for patients pre-treated with clopidogrel, especially in patients without acute coronary syndromes.As initial medical treatment of NSTEACS (12 trials with 33,176 participants), IIb/IIIa blockers did not decrease mortality at 30 days (OR 0.90, 95% CI 0.79 to 1.02) or at six months (OR 1.00, 95% CI 0.87 to 1.15), but slightly decreased death or myocardial infarction at 30 days (OR 0.91, 95% CI 0.85 to 0.98) and at six months (OR 0.88, 95% CI 0.81 to 0.96), although severe bleeding was increased (OR 1.29, 95% CI 1.14 to 1.45; ARI 1.4 per 1000).

AUTHORS' CONCLUSIONS

When administered during PCI, intravenous glycoprotein IIb/IIIa blockers reduce the risk of all-cause death at 30 days but not at six months, and reduce the risk of death or myocardial infarction at 30 days and at six months, at a price of an increase in the risk of severe bleeding. The efficacy effects are homogeneous but are less marked in patients pre-treated with clopidogrel where they seem to be effective only in patients with acute coronary syndromes. When administered as initial medical treatment in patients with NSTEACS, these agents do not reduce mortality although they slightly reduce the risk of death or myocardial infarction.

Platelet glycoprotein IIb/IIIa blockers during percutaneous coronary intervention and as the initial medical treatment of non-ST segment elevation acute coronary syndromes

BACKGROUND

During percutaneous coronary intervention (PCI), and in non-ST segment elevation acute coronary syndromes (NSTEACS), the risk of acute vessel occlusion by thrombosis is high. Glycoprotein IIb/IIIa blockers strongly inhibit platelet aggregation and may prevent mortality and myocardial infarction. This is an update of a Cochrane review first published in 2001, and previously updated in 2007 and 2010.

OBJECTIVES

To assess the efficacy and safety effects of glycoprotein IIb/IIIa blockers when administered during PCI, and as initial medical treatment in patients with NSTEACS.

SEARCH METHODS

We updated the searches of the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 12, 2012), MEDLINE (OVID, 1946 to January Week 1 2013) and EMBASE (OVID, 1947 to Week 1 2013) on 11 January 2013.

SELECTION CRITERIA

Randomised controlled trials comparing intravenous IIb/IIIa blockers with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed trial quality and extracted data. We collected major bleeding as adverse effect information from the trials. We used odds ratios (OR) and 95% confidence intervals (CI) for effect measures.

MAIN RESULTS

Sixty trials involving 66,689 patients were included. During PCI (48 trials with 33,513 participants) glycoprotein IIb/IIIa blockers decreased all-cause mortality at 30 days (OR 0.79, 95% CI 0.64 to 0.97) but not at six months (OR 0.90, 95% CI 0.77 to 1.05). All-cause death or myocardial infarction was decreased both at 30 days (OR 0.66, 95% CI 0.60 to 0.72) and at six months (OR 0.75, 95% CI 0.64 to 0.86), although severe bleeding was increased (OR 1.39, 95% CI 1.21 to 1.61; absolute risk increase (ARI) 8.0 per 1000). The efficacy results were homogeneous for every endpoint according to the clinical condition of the patients, but were less marked for patients pre-treated with clopidogrel, especially in patients without acute coronary syndromes.As initial medical treatment of NSTEACS (12 trials with 33,176 participants), IIb/IIIa blockers did not decrease mortality at 30 days (OR 0.90, 95% CI 0.79 to 1.02) or at six months (OR 1.00, 95% CI 0.87 to 1.15), but slightly decreased death or myocardial infarction at 30 days (OR 0.91, 95% CI 0.85 to 0.98) and at six months (OR 0.88, 95% CI 0.81 to 0.96), although severe bleeding was increased (OR 1.29, 95% CI 1.14 to 1.45; ARI 1.4 per 1000).

AUTHORS' CONCLUSIONS

When administered during PCI, intravenous glycoprotein IIb/IIIa blockers reduce the risk of all-cause death at 30 days but not at six months, and reduce the risk of death or myocardial infarction at 30 days and at six months, at a price of an increase in the risk of severe bleeding. The efficacy effects are homogeneous but are less marked in patients pre-treated with clopidogrel where they seem to be effective only in patients with acute coronary syndromes. When administered as initial medical treatment in patients with NSTEACS, these agents do not reduce mortality although they slightly reduce the risk of death or myocardial infarction.

Mechanisms of aspirin resistance

Aspirin is integral to the secondary prevention of cardiovascular disease and acts to impair the development of platelet-mediated atherothromboembolic events by irreversible inhibition of platelet cyclooxygenase-1 (COX-1). Inhibition of this enzyme prevents the synthesis of the potent pro-aggregatory prostanoid thromboxane A2. A large number of patients continue to experience atherothromboembolic events despite aspirin therapy, so-called 'aspirin treatment failure', and this is multifactorial in aetiology. Approximately 10% however do not respond appropriately to aspirin in a phenomenon known as 'aspirin resistance', which is defined by various laboratory techniques. In this review we discuss the reasons for aspirin resistance in a systematic manner, starting from prescription of the drug and ending at the level of the platelet. Poor medication adherence has been shown to be a cause of apparent aspirin resistance, and may in fact be the largest contributory factor. Also important is high platelet turnover due to underlying inflammatory processes, such as atherosclerosis and its complications, leading to faster regeneration of platelets, and hence of COX-1, at a rate that diminishes the efficacy of once daily dosing. Recent developments include the identification of platelet glycoprotein IIIa as a potential biomarker (as well as possible underlying mechanism) for aspirin resistance and the discovery of an anion efflux pump that expels intracellular aspirin from platelets. The absolute as well as relative contributions of such factors to the phenomenon of aspirin resistance are the subject of continuing research.

Aspirin and platelet adenosine diphosphate receptor antagonists in acute coronary syndromes and percutaneous coronary intervention: role in therapy and strategies to overcome resistance

Platelet activation and aggregation are key components in the cascade of events causing thrombosis following plaque rupture. Antiplatelet therapy is essential in the treatment of patients with acute coronary syndromes (ACS) and for those requiring percutaneous coronary intervention (PCI). Aspirin (acetylsalicylic acid) is a well established antiplatelet therapy and is mandated for secondary prevention of cardiovascular events following ACS. In patients with ACS, the addition of clopidogrel to aspirin is more effective than aspirin alone. For patients undergoing PCI, dual antiplatelet therapy with aspirin and clopidogrel is warranted. Aspirin should be continued indefinitely after PCI. Pretreatment of patients with clopidogrel prior to PCI lowers the incidence of cardiovascular events, yet the optimum timing of drug administration and dose are still being investigated, as is the duration of therapy following PCI. Late-stent thrombosis with drug-eluting stents has pushed the recommendation for duration of clopidogrel therapy up to 1 year and perhaps beyond, in patients without risks for bleeding. The concepts of aspirin and clopidogrel resistance are important clinical questions. No uniform definition exists for aspirin or clopidogrel resistance. Measurements of resistance are often highly variable and do not necessarily correlate with clinical resistance. Noncompliance remains the most prominent mode of resistance. Screening of selected patient populations for resistance or pharmacologic intervention of those patients termed 'resistant' warrants further study.

The association between prior use of aspirin and/or warfarin and the in-hospital management and outcomes in patients presenting with acute coronary syndromes: insights from the Global Registry of Acute Coronary Events (GRACE)

BACKGROUND

The role of acetylsalicylic acid (ASA [aspirin]) and warfarin in secondary prevention after acute coronary syndromes (ACS) is well established. However, there are sparse data comparing the presentation and outcomes of patients who present with ACS while on ASA and/or warfarin therapy and those on neither.

METHODS

Using data from the Canadian Global Registry of Acute Coronary Events (GRACE), we stratified 14,090 ACS patients into 4 groups according to prior use of antithrombotic therapies and compared in-hospital management and outcomes.

RESULTS

Among 14,090 ACS patients, 7411 (52.6%) were not on prior ASA or warfarin therapy, 5724 (40.6%) were on ASA only, 593 (4.2%) were on warfarin only, and 362 (2.6%) were on both ASA and warfarin. ACS patients taking ASA and/or warfarin were older with more comorbidities than the patients on neither drug. Patients receiving prior warfarin only or ASA and warfarin were less likely to receive guideline-recommended therapies. Patients who were taking prior warfarin only had higher unadjusted rates of death, death and/or reinfarction (re-MI), congestive heart failure (CHF), and major bleeding as compared with patients on no prior therapy. Furthermore, patients who were taking ASA and warfarin had higher unadjusted rates of death and/or re-MI and CHF than patients on prior ASA only.

CONCLUSIONS

ACS patients on prior warfarin are a high-risk population, yet they receive less guideline-recommended therapies and have higher unadjusted adverse event rates during their index hospitalization. With the increasing use of oral anticoagulants, clinical trials are needed to guide the optimal management of these ACS patients.

Impact of chronic antiplatelet therapy before hospitalization on ischemic and bleeding events in invasively managed patients with acute coronary syndromes: the ACUITY trial

AIMS

Presentation with an acute coronary syndrome (ACS) on chronic aspirin therapy is an independent predictor of adverse short-term outcomes. Whether this finding applies to chronic thienopyridine use, and with the contemporary invasive management of ACS, is unknown.

METHODS AND RESULTS

In ACUITY, 13819 patients with moderate and high-risk ACS were studied; patients transferred from an outside hospital were excluded from the present analysis, given uncertain preadmission antiplatelet status. Endpoints included major adverse cardiovascular events (MACE: death, myocardial infarction, or unplanned revascularization), major bleeding, and net adverse clinical events (NACE). Among 11313 study patients, 31 % were naive for antiplatelet agent, 49% were receiving aspirin alone, and 20% were on dual antiplatelet therapy. Chronic antiplatelet users were older and had a higher risk profile. After adjusting for baseline differences, chronic antiplatelet therapy (single or dual) was not associated with an increased incidence of 30-day MACE, bleeding, or NACE. However, patients on chronic aspirin or dual antiplatelet therapy at presentation had significantly higher 1-year rates of MACE [odds ratio (95% confidence interval) = 1.17 (1.01–1.36), P = 0.03 and 1.29 (1.02–1.64), P = 0.03, respectively]. Patients presenting on dual antiplatelet therapy had significantly greater adjusted MACE at 1-year than those on aspirin alone [odds ratio (95% confidence interval) = 1.34 (1.15–1.56), P < 0.0001].

CONCLUSION

Contrary to earlier studies, prior antiplatelet therapy was not associated with an increased risk of adverse outcomes at 30 days in invasively managed patients. Such use did, however, independently predict 1-year ischemic MACE, with outcomes worse for patients presenting on chronic dual antiplatelet therapy compared with aspirin alone.

Aspirin use is associated with an improved long-term survival in an unselected population presenting with unstable angina

BACKGROUND

Few published data are available on the benefits of aspirin use in patients with unstable angina (UA).

HYPOTHESIS

Aspirin use carries a mortality benefit in a population-based cohort of patients presenting with UA.

METHODS

All residents of Olmsted County, Minnesota presenting to local emergency departments with acute chest pain from January 1985 through December 1992 having symptoms consistent with UA were identified through medical records. A total of 1628 patients were identified with UA and were stratified by aspirin use in-hospital and at discharge. Cardiovascular mortality and nonfatal myocardial infarction and stroke were assessed over a median of 7.5 years follow-up and all-cause mortality data over a median of 16.7 years. The mean age of patients with UA was 65 years, and 60% were men.

RESULTS

After a median of 7.5 years follow-up, all-cause and cardiovascular-mortality rates were lower among patients prescribed versus not prescribed aspirin on discharge. There were 949 postdischarge deaths over the median follow-up of 16.7 years. After multivariable adjustment, aspirin use at discharge was associated with a lower long-term mortality (hazard ratio 0.78; 95% confidence interval, 0.65-0.93).

CONCLUSIONS

Aspirin use at hospital discharge following UA is associated with a reduction in long-term mortality. This long-term study extends prior trial results from select populations to a population-based cohort.

Relation of aspirin failure to clinical outcome and to platelet response to aspirin in patients with acute myocardial infarction

Aspirin failure, defined as occurrence of an acute coronary syndrome despite aspirin use, has been associated with a higher cardiovascular risk profile and worse prognosis. Whether this phenomenon is a manifestation of patient characteristics or failure of adequate platelet inhibition by aspirin has never been studied. We evaluated 174 consecutive patients with acute myocardial infarction. Of them, 118 (68%) were aspirin naive and 56 (32%) were regarded as having aspirin failure. Platelet function was analyzed after ≥72 hours of aspirin therapy in all patients. Platelet reactivity was studied by light-transmitted aggregometry and under flow conditions. Six-month incidence of major adverse coronary events (death, recurrent acute coronary syndrome, and/or stroke) was determined. Those with aspirin failure were older (p = 0.002), more hypertensive (p <0.001), more hyperlipidemic (p <0.001), and more likely to have had a previous cardiovascular event and/or procedure (p <0.001). Cumulative 6-month major adverse coronary events were higher in the aspirin-failure group (14.3% vs 2.5% p <0.01). Patients with aspirin failure had lower arachidonic acid-induced platelet aggregation (32 ± 24 vs 45 ± 30, p = 0.003) after aspirin therapy compared to their aspirin-naive counterparts. However, this was not significant after adjusting for differences in baseline characteristics (p = 0.82). Similarly, there were no significant differences in adenosine diphosphate-induced platelet aggregation and platelet deposition under flow conditions. In conclusion, our results suggest that aspirin failure is merely a marker of higher-risk patient profiles and not a manifestation of inadequate platelet response to aspirin therapy.

Prior aspirin use and outcomes in acute coronary syndromes

OBJECTIVES

The purpose of this study was to determine whether patients taking aspirin before an acute coronary syndrome (ACS) are at higher risk of recurrent events or mortality.

BACKGROUND

Controversy exists whether prior aspirin use is an independent predictor of worse outcomes in patients who experience an ACS.

METHODS

We evaluated 66,443 ACS patients from a merged database of previous Thrombolysis in Myocardial Infarction trials. We evaluated the differences in ACS type, total mortality, and the composite end point of death, myocardial infarction (MI), recurrent ischemia, or stroke between prior aspirin and nonprior aspirin users. We used multivariate analysis to control for differences in baseline characteristics.

RESULTS

Prior aspirin users (n = 17,839) were older (63 years vs. 59 years) and had more coronary risk factors and evidence of coronary artery disease (MI, angina, prior intervention) than nonprior aspirin users (n = 48,604) (all p < 0.0001). Prior aspirin use was associated with less severe types of ACS at presentation (e.g., unstable angina > non-ST-segment elevation MI > ST-segment elevation MI) than their nonaspirin user counterparts (p < 0.0001). After multivariate analysis, there was no difference in total mortality between prior aspirin users and nonaspirin users at day 30 (odds ratio [OR]: 1.01; 95% confidence interval [CI]: 0.90 to 1.13) or by the last follow-up visit (mean 328 days) (hazard ratio: 1.03; 95% CI: 0.95 to 1.11). Prior aspirin use was modestly associated with recurrent MI (OR: 1.26; 95% CI: 1.12 to 1.43) and the composite end point (OR: 1.16; 95% CI: 1.08 to 1.24).

CONCLUSIONS

Prior aspirin use was associated with more comorbidities and coronary disease and a higher risk of recurrent MI, but not mortality. As such, it should best be considered a marker of a patient population at high risk for recurrent adverse events after ACS.

Platelet glycoprotein IIb/IIIa blockers during percutaneous coronary intervention and as the initial medical treatment of non-ST segment elevation acute coronary syndromes

BACKGROUND

During percutaneous coronary intervention (PCI), and in non-ST segment elevation acute coronary syndromes (NSTEACS), the risk of acute vessel occlusion by thrombosis is high. IIb/IIIa blockers strongly inhibit platelet aggregation and may prevent mortality and myocardial infarction (MI). This is an update of a Cochrane review first published in 2001, and previously updated in 2007.

OBJECTIVES

To assess the effects and safety of IIb/IIIa blockers when administered during PCI, and as initial medical treatment in patients with NSTEACS.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 3, 2009), MEDLINE (1966 to October 2009), and EMBASE (1980 to October 2009).

SELECTION CRITERIA

Randomised controlled trials comparing intravenous IIb/IIIa blockers with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed trial quality and extracted data. We collected major bleeding as adverse effect information from the trials. Odds ratios (OR) and 95% confidence intervals (CI) were used for effect measures.

MAIN RESULTS

Forty-eight trials involving 62,417 patients were included. During PCI, IIb/IIIa blockers decreased mortality at 30 days (OR 0.76, 95% CI 0.62 to 0.95) and at six months (OR 0.84, 95% CI 0.71 to 1.00). Death or MI was decreased both at 30 days (OR 0.65, 95% CI 0.60 to 0.72), and at 6 months (OR 0.70, 95% CI 0.61 to 0.81), although severe bleeding was increased (OR 1.38, 95% CI 1.20 to 1.59; absolute risk increase (ARI) 8.0 per 1000). The efficacy results were homogeneous for every endpoint according to the clinical condition of the patients, but were less marked for patients pre-treated with clopidogrel, especially in patients without ACS.As initial medical treatment of NSTEACS, IIb/IIIa blockers did not decrease mortality at 30 days (OR 0.91, 95% CI 0.80 to 1.03) or at six months (OR 1.00, 95% CI 0.87 to 1.15), but slightly decreased death or MI at 30 days (OR 0.92, 95% CI 0.86 to 0.99) and at six months (OR 0.88, 95% CI 0.81 to 0.96), although severe bleeding was increased (OR 1.27, 95% CI 1.12 to 1.43; ARI 1.4 per 1000).

AUTHORS' CONCLUSIONS

When administered during PCI, intravenous IIb/IIIa blockers reduce the risk of death and of death or MI at 30 days and at six months, at a price of an increase in the risk of severe bleeding. The efficacy effects are homogeneous but are less marked in patients pre-treated with clopidogrel where they seem to be effective only in patients with ACS. When administered as initial medical treatment in patients with NSTEACS, these agents do not reduce mortality although they slightly reduce the risk of death or MI.

Significance of mean platelet volume on prognosis of patients with and without aspirin resistance in settings of non-ST-segment elevated acute coronary syndromes

Platelet volume is a marker of platelet function and activation. An elevated mean platelet volume (MPV) is associated with acute coronary syndromes (ACS). Recurrent cardiovascular events were found to be higher in patients with aspirin resistance. In this study, we investigated the effect of MPV on prognosis of patients with and without aspirin resistance by PFA-100 in settings of non-ST-segment elevated ACS. Two hundred and twenty patients with ACS were followed for an average of 14.86 +/- 5.93 months for the occurrence of death, myocardial infarction (MI) and revascularization. Aspirin effect on platelet function was assessed by PFA-100. According to MPV value and aspirin resistance status, patients were divided into four groups. Group 4 (with an elevated MPV and aspirin resistance) was significantly associated with worse prognosis for composite endpoint (death, MI and revascularization), death and MI (for all, log-rank P < 0.0001). Multivariate analysis showed that presence of an elevated MPV and aspirin resistance was an independent predictor of composite endpoint [hazard ratio 8.21, 95% confidence interval (CI) 3.48-19.35, P < 0.0001], death (hazard ratio 5.48, 95% CI 1.62-18.53, P = 0.006) and MI (hazard ratio 4.44, 95% CI 1.57-12.58, P = 0.005). Presence of an elevated MPV and aspirin resistance was significantly associated with death, MI and the composite endpoint, due to the lack of beneficial effect of aspirin on activated platelets. Patients with ACS, especially in the presence of an elevated MPV may benefit from the evaluation of aspirin resistance for risk stratification.

The clinical importance of laboratory-defined aspirin resistance in patients presenting with non-ST elevation acute coronary syndromes

In this study, we aimed to assess the factors associated with laboratory-defined aspirin resistance and the relationship of this laboratory-defined aspirin resistance with thrombolysis in myocardial infarction risk score, markers of cardiac necrosis, and inflammatory and thrombotic risk factors in patients with unstable angina or non-ST elevation myocardial infarction. Ninety-seven patients who were under aspirin therapy and hospitalized with unstable angina/non-ST elevation myocardial infarction were included in the study. Laboratory-defined aspirin sensitive and resistant groups were determined by platelet function analyzer; aspirin resistance was defined as collagen/epinephrine closure time less than 165 s. Laboratory-defined aspirin resistance was noted in 29 patients (29.9%), and non-ST elevation myocardial infarction was observed in 46 patients (47.4%). Patients in the group with laboratory-defined aspirin resistance had significantly higher thrombolysis in myocardial infarction risk scores (P < 0.001). When the details of cardiac myonecrosis markers were compared, baseline and follow-up creatine kinase-myocardial band and troponin I values were higher in laboratory-defined aspirin-resistant group. Multivariate analyses revealed that laboratory-defined aspirin resistance was an independent predictor of non-ST elevation myocardial infarction (P = 0.022). Laboratory-defined aspirin resistance is associated with non-ST elevation myocardial infarction, higher markers of cardiac necrosis and thrombolysis in myocardial infarction risk score in patients hospitalized with unstable angina/non-ST elevation myocardial infarction.

Impact of chronic antithrombotic therapy on hospital course of patients with acute myocardial infarction

BACKGROUND

Little is known about the influence of chronic antithrombotic therapy on treatment and clinical outcome in patients with acute ST-elevation myocardial infarction (STEMI).

HYPOTHESIS

The purpose of this study was to investigate the hospital course of STEMI patients on antithrombotics.

METHODS

We analyzed data of consecutive patients with STEMI, who were prospectively enrolled in the German Acute Coronary Syndromes registry between July 2000 and November 2002. Overall, 8224 patients were stratified into 3 groups: group 1 had no prior chronic antithrombotic medication (n = 6004), group 2 was on chronic acetylsalicylic acid (ASA) therapy (n = 2022), and group 3 was on chronic oral anticoagulation therapy (n = 198).

RESULTS

Patients on antithrombotic medication were older and had a higher baseline risk profile. The rate of patients receiving early reperfusion (group 1: 74.6%, group 2: 61.2%, group 3: 52.0%) and guideline-adherent adjustment therapy was lower among patients on antithrombotics. Age and left bundle branch block were strong negative predictors for early reperfusion therapy in patients with prior antithrombotic treatment. Infarct size measured by peak creatine kinase level was lower in patients on antithrombotics. Hospital mortality (group 1: 8.0%, group 2: 12.8%, group 3: 16.2%) and major bleeding complications (group 1: 1.6%, group 2 2.0%, group 3 4.1%) were highest in patients on oral anticoagulants. However, after adjustment for confounding factors, prior ASA (odds ratio [OR]: 0.98, 95% confidence interval [CI]: 0.80-1.21) and oral anticoagulant treatment (OR: 1.06, 95% CI: 0.66-1.71) were not independent predictors for in-hospital death.

CONCLUSIONS

Despite a higher risk profile, patients with STEMI on a chronic antithrombotic therapy were less likely to receive early reperfusion therapy. However, after adjustment, prior ASA or oral anticoagulant therapy was not associated with higher in-hospital mortality.

Acute coronary syndromes: diagnosis and management, part I

The term acute coronary syndrome (ACS) refers to any group of clinical symptoms compatible with acute myocardial ischemia and includes unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). These high-risk manifestations of coronary atherosclerosis are important causes of the use of emergency medical care and hospitalization in the United States. A quick but thorough assessment of the patient's history and findings on physical examination, electrocardiography, radiologic studies, and cardiac biomarker tests permit accurate diagnosis and aid in early risk stratification, which is essential for guiding treatment. High-risk patients with UA/NSTEMI are often treated with an early invasive strategy involving cardiac catheterization and prompt revascularization of viable myocardium at risk. Clinical outcomes can be optimized by revascularization coupled with aggressive medical therapy that includes anti-ischemic, antiplatelet, anticoagulant, and lipid-lowering drugs. Evidence-based guidelines provide recommendations for the management of ACS; however, therapeutic approaches to the management of ACS continue to evolve at a rapid pace driven by a multitude of large-scale randomized controlled trials. Thus, clinicians are frequently faced with the problem of determining which drug or therapeutic strategy will achieve the best results. This article summarizes the evidence and provides the clinician with the latest information about the pathophysiology, clinical presentation, and risk stratification of ACS and the management of UA/NSTEMI.

Acute coronary syndromes: diagnosis and management, part I

The term acute coronary syndrome (ACS) refers to any group of clinical symptoms compatible with acute myocardial ischemia and includes unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). These high-risk manifestations of coronary atherosclerosis are important causes of the use of emergency medical care and hospitalization in the United States. A quick but thorough assessment of the patient's history and findings on physical examination, electrocardiography, radiologic studies, and cardiac biomarker tests permit accurate diagnosis and aid in early risk stratification, which is essential for guiding treatment. High-risk patients with UA/NSTEMI are often treated with an early invasive strategy involving cardiac catheterization and prompt revascularization of viable myocardium at risk. Clinical outcomes can be optimized by revascularization coupled with aggressive medical therapy that includes anti-ischemic, antiplatelet, anticoagulant, and lipid-lowering drugs. Evidence-based guidelines provide recommendations for the management of ACS; however, therapeutic approaches to the management of ACS continue to evolve at a rapid pace driven by a multitude of large-scale randomized controlled trials. Thus, clinicians are frequently faced with the problem of determining which drug or therapeutic strategy will achieve the best results. This article summarizes the evidence and provides the clinician with the latest information about the pathophysiology, clinical presentation, and risk stratification of ACS and the management of UA/NSTEMI.

Clopidogrel provides significantly greater inhibition of platelet activity than aspirin when combined with atorvastatin after coronary artery bypass grafting: a prospective randomized study

OBJECTIVE

We aimed to compare the effects of 2 different antiplatelet agents on platelet activity in patients receiv- ing atorvastatin after coronary artery bypass grafting (CABG).

METHODS

We prospectively randomized 50 patients undergoing CABG into 2 groups; group 1 started to receive atorvastatin (10 mg) plus clopidogrel (75 mg; C + A, n = 25) and group 2 atorvastatin (10 mg) and acetylsalicylic acid (ASA; 300 mg, ASA + A, n = 25) daily on postoperative day 1 and continued for 6 months after operation. Adenosine diphosphate (ADP)-induced platelet aggregation and the expressions of glycoprotein (Gp) IIb, GpIIIa, P-selectin, and fibrinogen (Fg) and low-density lipoprotein (LDL) binding to platelets were assessed preoperatively and at postoperative days 7, 90, and 180.

RESULTS

The mean age of the patients was 59.6 +/- 7.6 years, and 82% of the patients were males. The combination of C + A markedly inhibited ADP-induced platelet aggregation compared with ASA + A at postoperative days 90 and 180 (52% +/- 6.0% vs 56% +/- 7.25% and 19.6% +/- 3.2% vs 37% +/- 4.1%, P = .039 and P = .0001, respectively). The therapy of C + A significantly suppressed the expressions of GpIIIa at postoperative days 7, 90, and 180 (P = .0001, P = .0001, and P = .0001, respectively) and P-selectin at postoperative days 90 and 180 (P = .035 and P = .002, respectively) when compared to ASA + A. The expression of GpIIb was also significantly depressed at postoperative day 180 in group 1 when compared to group 2 (P = .0001). Low-density lipoprotein binding was significantly increased at day 180 postoperatively in both the groups (basal: 42.9% +/- 5.6% vs 45.3% +/- 4.4% and day 180: 60.3% +/- 4.6% vs 61.8% +/- 5.7%, P = .0001).

CONCLUSIONS

Our results demonstrate that the combination of C + A is more effective than that of ASA + A in inhibiting ADP-mediated platelet aggregation and expression of major platelet receptors after CABG.

Aspirin resistance: an update

Aspirin resistance (AR) still lacks a universally accepted definition, but it may be discussed as either a laboratory phenomenon or a clinical presentation. Laboratory resistance is mainly defined as abnormal platelet response to aspirin, whereas the clinical manifestation is the failure of aspirin to prevent cardiovascular events. Although there is evidence of an association, it appears that a laboratory abnormality in platelet function is not the only risk factor for the clinical manifestation of AR. Therapies for primary and secondary prevention of AR still need to be elucidated, but there are some data to suggest that in an acute episode of aspirin failure because of AR, different therapeutic interventions need to be considered.

Balancing myocardial ischemic and bleeding risks in patients with non-ST-segment elevation myocardial infarction

Achieving an appropriate balance of anti-ischemic efficacy versus bleeding risk with antiplatelet and anticoagulant agents demands an accurate estimation of risks. Although traditional risk stratification is available to decrease complications, and various methods of stratifying these risks have been proposed and validated, the stratification of bleeding risk is in its infancy. However, no model currently available permits the simultaneous estimation of these risks. Ischemic risk may be determined using 1 of several validated models, followed by the estimation of bleeding risk according to known risk factors. After selecting appropriate pharmacotherapy on the basis of the stratification of these risks, attention must be paid to proper dosing according to individual risk factors and patient, clinical, and technical variables. The aim of this study was to examine risk stratification models for these parameters to determine clinical characteristics common to ischemia and bleeding that can be used to minimize risks. A "bleeding risk subscale" is proposed, with factors extrapolated from current ischemic risk models, to integrate ischemic mortality and bleeding risk in patients with non-ST-segment elevation acute coronary syndromes. In conclusion, a validated tool to simultaneously evaluate ischemic and bleeding risk will help determine the most well-balanced pharmacotherapy for patients with non-ST-segment elevation acute coronary syndromes.

Aspirin resistance in atherosclerosis

Clinically, aspirin resistance is defined as the failure of aspirin therapy to prevent an acute vascular thrombotic event despite regular intake of appropriate doses. In the laboratory, aspirin resistance encompasses the drug's failure to attain a particular level of platelet inhibition. From a clinical standpoint, the inability of aspirin to prevent a thrombotic event, despite appropriate cyclooxygenase-1 inhibition, implies the involvement of other factors. Evidence is emerging that aspirin resistance, as defined by residual platelet activity, merely reflects an individual's enhanced basal platelet function and suggests a hereditary component. Due to the multifactorial nature of cardiovascular disease, it is likely that a single therapy like aspirin cannot fully treat and prevent all thrombotic complications in the setting of atherosclerosis.

The role of aspirin resistance in the treatment of acute coronary syndromes

The TIMI Risk Score recognizes prior aspirin use as an independent risk factor for adverse outcomes in subjects presenting with an acute coronary syndrome. The etiology of this increased risk awaits clarification, but prior aspirin use may be associated with altered thrombus composition which is more resistant to current treatment modalities as compared to thrombus formation in subjects without prior aspirin use. Post hoc analysis of acute coronary syndrome trials has shown that prior aspirin users treated with unfractionated heparin are at particularly high risk. The addition of glycoprotein IIb/IIIa receptor inhibitor to unfractionated heparin or substitution of low-molecular-weight heparin significantly improves outcomes in prior aspirin users. The prognostic significance of prior aspirin use in acute coronary syndromes has important implications not only in clinical practice, but also in the design and interpretation of clinical trials.

Failure of aspirin to prevent myocardial infarction and adverse outcome during follow-up - a large series of all-comers

BACKGROUND

Aspirin has been used for secondary prevention of myocardial infarction (MI) in individuals with coronary disease. Although supported by several large controlled trials, aspirin prevents only a portion of recurrent events.

AIM AND METHOD

We set out to study the prevalence of long-term aspirin use prior to admission for MI and its significance for medium-term event-free survival; 998 consecutive patients with acute MI admitted to a tertiary center were included in the study.

RESULTS

Nearly half (42.4%) of all patients reported long-term use of low-dose aspirin prior to the index event. Prior aspirin use was associated with a 50% increase in the risk of both the combined end point of recurrent unstable angina, recurrent myocardial infarction, stroke, or death (OR 1.49; 95% CI 1.12-2.00, P=0.006) and mortality (OR 1.50; 95% CI 1.03-2.17, P=0.03) during 10-month follow-up. Prior aspirin use was not associated with an increased frequency of added antithrombotic therapy at discharge.

CONCLUSIONS

We have found that prior aspirin use is common in patients hospitalized for acute MI. Individuals already on aspirin had increased risk of recurrent ischemic events and all-cause mortality during the 10-month follow-up after their index MI.

Role of mean platelet volume in triagging acute coronary syndromes

BACKGROUND

Acute coronary syndromes, characterized by the rupture of unstable plaque and the subsequent thrombotic process involving platelets, have been increasing in relative frequency. The central role of platelet activation has long been noticed in this pathophysiology; hence, many therapies have been directed against it. In this study, we have aimed to search prospectively the value of mean platelet volume (MPV), which is a simple and accurate measure of the functional status of platelets, in patients hospitalized with diagnosis of acute coronary syndromes (ACS).

MATERIALS AND METHODS

A total of 216 consecutive patients (156 male, 60 female) hospitalized with the diagnosis of non-ST segment elevation (NSTE) ACS within the first 24 h of their chest pain were enrolled. One hundred and twenty patients, matched according to sex and age, with stable coronary heart disease (CHD) (85 male, 35 female) were enrolled as a control group. Patients were classified into two group: those with unstable angina (USAP, n = 105) and those with non-ST segment elevation myocardial infarction (NSTEMI, n = 111).

RESULTS

MPVs were 10.4 +/- 0.6 fL, 10 +/- 0.7 fL, 8.9 +/- 0.7 fL consecutively for NSTEMI, USAP and stable CHD with significant differences. Patients with ischemic attacks in the first day of hospitalization accompanied by >0.05 mV ST segment shift had significantly higher MPV compared to those without such attacks (P = 0.001). Multivariable logistic regression analysis yielded that MPV (P = 0.016), platelet count (P < 0.001), and the presence of >0.05 mV ST segment depression at admission (P = 0.002) were independent predictors of development of NSTEMI in patients presenting with NSTE ACS.

CONCLUSION

In patients presenting with NSTE ACS, higher MPV, though there are overlaps among subgroups, indicates not only more risk of having NSTEMI but also ischemic complications.

The effect of acetylsalicylic acid resistance on prognosis of patients who have developed acute coronary syndrome during acetylsalicylic acid therapy

AIM

The relationships between clinical events and acetylsalicylic acid resistance (AR), as well as its frequency, have been established in stable patients with coronary artery disease (CAD). Although acute coronary syndrome (ACS) patients taking acetylsalicylic acid have been accepted as a high-risk population, the role of AR has not been investigated in these patient groups. Thus, in the present study, the impact of AR was investigated in patients with ACS who were taking acetylsalicylic acid.

METHODS

Between January 2001 and February 2003, 140 ACS patients were included in the present prospective study. All patients had ACS while taking acetylsalicylic acid. Coronary angiographic scores for severity and extent of CAD were determined for all patients. The effect of acetylsalicylic acid on platelet function was assessed by the platelet function analyzer PFA-100 (Dade Behring, USA). The primary end point was the composite of death, myocardial infarction, cerebrovascular accident and revascularization. The mean follow-up period was 20 months.

RESULTS

Patients with AR were older than patients without AR (63.8+/-10.8 years versus 58.3+/-11.2 years; P=0.005). Moreover, myocardial damage was higher in patients with AR according to cardiac troponin T values (1.11+/-1.3 mug/L versus 0.41+/-0.5 mug/L; P=0.01). The composite end point of death, myocardial infarction, cerebrovascular accident or revascularization was present in 16 of 45 patients (35%) with AR and in 13 of 79 patients (16%) without AR (hazard ratio 2.46, 95% CI 1.18 to 5.13; P=0.016). After adjustment for age, platelet count, cardiac troponin T value and CAD severity score, AR remained an independent predictor for long-term adverse events (hazard ratio 3.03, 95% CI 1.06 to 8.62; P=0.038).

CONCLUSIONS

The clinical event rate was found to be higher in ACS patients with AR than in those without AR. Thus, it may be concluded that there is a strong correlation between a worse prognosis and AR in these patients.

Aspirin resistance

Aspirin resistance refers to less than expected suppression of thromboxane A(2) production by aspirin and has been reported to be independently associated with an increased risk of adverse cardiovascular events. Possible causes of aspirin resistance include poor compliance, drug interaction, inadequate aspirin dose, increase turnover of platelets, genetic polymorphisms of cyclo-oxygenase-1, and upregulation of alternate (non-platelet) pathways of thromboxane production. Laboratory methods used to detect aspirin resistance include those that measure thromboxane A(2) production and thromboxane A(2)-dependent platelet function. However, since there is currently no standardised approach to the diagnosis and there are no proven effective treatments for aspirin resistance that improve outcome, patients with cardiovascular disease receiving aspirin should not be routinely tested for aspirin resistance. Instead physicians should be aware of the factors that may impair aspirin function, ensure that they use an appropriate dose of aspirin and optimise compliance with aspirin therapy. Further research exploring the mechanisms of aspirin resistance is needed in order to better define and develop a standardised test for aspirin resistance that is specific, reliable, can be readily applied in routine laboratories and correlate with an increased risk of cardiovascular events.

Aspirin resistance or variable response or both?

Numerous clinical trials have demonstrated that aspirin is effective in secondary prevention and in high-risk primary prevention of adverse cardiovascular events. However, a constellation of clinical and laboratory evidence exists that demonstrates diminished or absent response to aspirin in some patients. This has led to the concept of "aspirin resistance," which is a poorly defined, somewhat misleading term. The mechanism for aspirin resistance has not been fully established, but it is almost certainly due to a combination of clinical, biological, and genetic properties affecting platelet function. There are no criteria for distinguishing true resistance from treatment failure, and there is no consensus on whether the definition of aspirin resistance should be based on clinical outcomes, laboratory evidence, or both. Studies in large populations are needed to define antiplatelet resistance using consistent and reproducible assays and correlate the measurements with clinical outcomes. One such prospective randomized trial is completed, and 2 others are under way: the Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance (CHARISMA) trial compared clopidogrel and aspirin with placebo and aspirin for high-risk primary or secondary prevention, and the Aspirin Nonresponsiveness and Clopidogrel Endpoint Trial (ASCET) is evaluating whether switching to clopidogrel will be superior to continued aspirin therapy in improving clinical outcomes in aspirin-resistant patients with angiographically documented coronary artery disease. The Research Evaluation to Study Individuals Who Show Thromboxane or P2Y(12) Receptor Resistance (RESISTOR) trial is investigating whether modifying antiplatelet regimens could prevent myonecrosis after percutaneous coronary intervention in patients with aspirin and clopidogrel resistance.

POINT OF CARE TESTING OF ASPIRIN RESISTANCE IN PATIENTS WITH VASCULAR DISEASE

INTRODUCTION

The reported range in rates of aspirin resistance (5.5-60%) may reflect difficulties in studying platelet function and the variety of tests used. This study used a platelet function analyzer (PFA-100) to prospectively document aspirin resistance in a cohort of patients with arterial disease.

METHODS

Patients with internal carotid artery (ICA) stenosis or intermittent claudication (IC) were recruited. Exclusion criteria were contraindications to aspirin, prescription of other medication with known antiplatelet effects or known platelet abnormalities. After prescription of 100 mg aspirin/day for 2 weeks an uncuffed venous blood sample was taken and analysed with the PFA-100. Aspirin resistance was defined as closure time (CT) less than the upper limit of normal (158 s collagen/epinephrine agonist; 118 s collagen/adenosine diphosphate (ADP) agonist).

RESULTS

Thirty-three patients with IC and 12 patients with ICA stenosis were recruited (n = 45). Median (range) age was 74 years (49-85) and the male to female ratio was 1.5:1. The median (range) CT was >300 (85 to >300) s with collagen/epinephrine and 100 (52 to >300) s with collagen/ADP agonist. Twelve patients (27%) in the collagen/epinephrine group had normal CT despite treatment with 100 mg aspirin, indicating resistance. Of the 33 patients with collagen/epinephrine CT prolonged by aspirin, 10 patients also had prolonged collagen/ADP CT, suggesting excessive platelet inhibition.

CONCLUSION

A significant proportion of patients taking aspirin do not show laboratory evidence of platelet inhibition and may not be protected from atherothrombotic events. The PFA-100 appears to be a useful tool to screen for both aspirin resistance and excessive aspirin mediated platelet inhibition.

Prior clopidogrel use and outcome of acute coronary syndrome

BACKGROUND

Prior aspirin use has been associated with poorer outcome in acute coronary syndrome, and forms part of the TIMI Risk Score. It is not known if prior use of clopidogrel is associated with similar risk.

AIM

To assess if prior clopidogrel use is associated with higher risk in acute coronary syndrome.

PARTICIPANTS

Participants were 869 consecutive admissions to a Scottish district general hospital with suspected acute coronary syndrome.

METHODS

Incidence of death, recurrent myocardial infarction or urgent percutaneous intervention at 2 weeks was recorded. Odds ratios for sub-groups on clopidogrel, aspirin or neither were calculated.

RESULTS

Odds ratios were: clopidogrel 1.46 (95% ci 0.62-3.33), aspirin 1.09 (95% ci 0.64-1.85), neither 0.91 (95% ci 0.53-1.54).

CONCLUSION

No definite association was shown between clopidogrel use and outcome but there was a trend towards increased risk of major acute coronary events.

Aspirin resistance measured by cationic propyl gallate platelet aggregometry and recurrent cardiovascular events during 4 years of follow-up

BACKGROUND

Aspirin resistance appears to be an important prognostic factor in patients with coronary artery disease, yet there is no standardized method to measure it and limited data on its correlation to clinical outcomes.

METHODS

In a prospective study we followed 103 patients (mean age 64 years) with acute coronary syndrome (ACS) without ST segment elevation who were treated with 100 mg of aspirin (ASA) daily. Optical platelet aggregometry using cationic propyl gallate (CPG) as an inductor was measured at ACS onset and after 3, 12, 24, 36, and 48 months. ASA responsiveness was defined both by the slope of the aggregation curve (<53%/min) and by spontaneous aggregation (<5%). The primary outcomes were the recurrence of ACS or stroke.

RESULTS

Patients with ACS exhibited a greater prevalence of ASA resistance (55%) than healthy volunteers (4%; p<0.01). ASA resistance occurred more often in patients with type 2 diabetes, hypertriacylglycerolemia, and decreased HDL levels, and in smokers (p<0.05). A single assessment of platelet aggregometry was sufficient to identify ASA-resistant patients. During the 4-year follow-up, the patients with ASA resistance had an 88% incidence of recurrent cardiovascular events versus 46% for the patients without ASA resistance (p<0.01). In the subgroup with recurrent cardiovascular (CV) events, significantly more patients were ASA-resistant than in the subgroup without recurrent CV events (72% vs. 8%, p<0.01).

CONCLUSION

ASA resistance measured by CPG-induced platelet aggregometry is more common among patients with ACS and some metabolic risk factors, and ASA-resistant patients have a significantly higher recurrence of cardiovascular events.

Prevalence of aspirin resistance in patients with an evolving acute myocardial infarction

OBJECTIVE

To study the prevalence and importance of aspirin resistance in patients with an evolving acute myocardial infarction (AMI) by use of the Platelet Function Analyzer-100.

INTRODUCTION

Previous studies have demonstrated the existence of aspirin resistance, but the clinical relevance of the phenomenon remains to be clarified. If aspirin resistant patients comprise a high-risk subgroup, it might be expected that the prevalence of aspirin resistance in patients with AMI would be higher than in patients without AMI. We hypothesized that the prevalence of aspirin resistance in patients with AMI was twice the prevalence in patients without AMI.

METHODS

We included 298 consecutive patients with known cardiovascular disease who were admitted to hospital with symptoms suggestive of an AMI. All had been taking aspirin 150 mg/day for at least 7 days prior to hospital admission. Platelet function was measured immediately at admission, and aspirin resistance was defined as a collagen/epinephrine Closure Time (CT(CEPI))<165 s.

RESULTS

We found that 70 (23.5%) patients were aspirin resistant, and 70 (23.5%) patients ended up with the diagnosis of an AMI. The prevalence of aspirin resistance was significantly higher in patients with AMI as compared to patients without (36% versus 20%, OR 2.26, CI 95% 1.19-4.22, p=0.0058). The CT(CEPI) measured at admission was an independent factor associated with an AMI.

CONCLUSIONS

Aspirin resistance is present in almost one fourth of patients admitted to hospital with symptoms suggestive of an AMI, and aspirin resistance is significantly associated with the diagnosis of a definite AMI.

Antiplatelet therapy in peripheral occlusive arterial disease

BACKGROUND

Antiplatelet therapy (APT) in patients with peripheral occlusive arterial disease (POAD) may reduce cardiovascular (CV) morbidity and mortality by inhibiting atherothrombosis. This article reviews the current evidence for APT in patients with stable POAD and in patients undergoing revascularization procedures for POAD.

METHODS

A Medline and Pubmed literature search (January 1966 to February 2003) was conducted to identify articles relating APT and POAD. Manual cross referencing was also used.

RESULTS AND CONCLUSIONS

Meta-analyses suggest that APT (most commonly aspirin) in patients with stable POAD significantly reduces the incidence of nonfatal stroke, myocardial infarction and CV death. However, this conclusion is based on subset analysis of data predominantly involving patients with coronary and cerebrovascular atherosclerosis. There is a little direct evidence for the use of aspirin in patients with isolated POAD, but in practice, aspirin remains the most commonly used antiplatelet agent as high rates of coronary and cerebrovascular diseases are observed in this patient population. For patients with POAD without additional indicators of vascular risk, the protective effect of aspirin is unclear and dependent on the balance of risks and benefits in the individual patient. For patients undergoing peripheral revascularization, ticlopidine and aspirin in combination with dipyridamole are effective in maintaining patency after bypass procedures and following angioplasty/femoral endarterectomy. The efficacy of thienopyridines in peripheral angioplasty is uncertain, and the optimum timing and duration of APT relative to intervention are not known.