Platelet function tests are not equally effective in measuring aspirin's antiplatelet effect and correlate poorly amongst themselves. The clinical usefulness of the different assays to classify correctly patients as aspirin resistant remains undetermined.

Current available data show that about 4% to 30% of patients treated with conventional doses of clopidogrel do not display adequate antiplatelet response. Clopidogrel resistance is a widely used term that remains to be clearly defined. So far, it has been used to reflect failure of clopidogrel to achieve its antiaggregatory effect. The interpatient variability in clopidogrel response is multifactorial. It can be due to extrinsic or intrinsic mechanisms. Among extrinsic mechanisms are the possibility of clopidogrel underdosing in patients undergoing stenting or with acute coronary syndrome, and drug-drug interactions involving CYP3A4. Intrinsic mechanisms include genetic polymorphisms of the P2Y(12) receptor and of the CYP3As, accrued release of adenosine diphosphate, or up-regulation of other platelet activation pathways. Presently, there is no definite demonstration of an association between low responsiveness to clopidogrel and thrombotic events. The optimal level of clopidogrel-induced platelet inhibition, which will correlate quantitatively with clopidogrel's ability to prevent atherothrombotic events is still lacking. Furthermore, because there is no single and validated platelet function assay to measure clopidogrel's antiplatelet effect, it is not justified to routinely look for clopidogrel resistance in the clinical setting. This review discusses currently available evidence surrounding the variability in the antiplatelet response to clopidogrel.

Antiplatelet therapy (APT) has become an important tool in the treatment and prevention of atherosclerotic events, particularly those associated with coronary artery disease. A large evidence base has evolved regarding the relationship between APT prescription in various clinical contexts and risk/benefit relationships. The Guidelines Committee of the Canadian Cardiovascular Society and Canadian Association of Interventional Cardiology publishes regular updates of its recommendations, taking into consideration the most recent clinical evidence. The present update to the 2011 and 2013 Canadian Cardiovascular Society APT guidelines incorporates new evidence on how to optimize APT use, particularly in situations in which few to no data were previously available. The recommendations update focuses on the following primary topics: (1) the duration of dual APT (DAPT) in patients who undergo percutaneous coronary intervention (PCI) for acute coronary syndrome and non-acute coronary syndrome indications; (2) management of DAPT in patients who undergo noncardiac surgery; (3) management of DAPT in patients who undergo elective and semiurgent coronary artery bypass graft surgery; (4) when and how to switch between different oral antiplatelet therapies; and (5) management of antiplatelet and anticoagulant therapy in patients who undergo PCI. For PCI patients, we specifically analyze the particular considerations in patients with atrial fibrillation, mechanical or bioprosthetic valves (including transcatheter aortic valve replacement), venous thromboembolic disease, and established left ventricular thrombus or possible left ventricular thrombus with reduced ejection fraction after ST-segment elevation myocardial infarction. In addition to specific recommendations, we provide values and preferences and practical tips to aid the practicing clinician in the day to day use of these important agents.

The assessment of platelet function inhibition by clopidogrel is highly test-specific. Decision to increase clopidogrel dosage may vary on the basis of the assay used, thus highlighting the need for unambiguous guidelines with respect to assay selection, as platelet function assays are not interchangeable. At present, platelet function testing evaluating clopidogrel efficacy cannot be recommended in routine clinical practice.

Patients with chest pain, normal epicardial coronary arteries, and reduced vasodilation in response to atrial pacing appear to have associated endothelial dysfunction of the coronary microvasculature. Thus, microvascular endothelial dysfunction may contribute to the reduced vasodilator reserve with atrial pacing and anginal chest pain in these patients.

These data indicate that same-day rest/stress sestamibi imaging will incorrectly identify 36% of myocardial regions as being irreversibly impaired and nonviable compared with both thallium redistribution/reinjection and PET. However, the identification of reversible and viable myocardium can be greatly enhanced with sestamibi if an additional redistribution image is acquired after the rest sestamibi injection or if the severity of reduction in sestamibi activity within irreversible defects is considered.

Out of hospital cardiac arrest (OHCA) is associated with a low rate of survival to hospital discharge and high rates of neurological morbidity among survivors. Programmatic efforts to institute and integrate OHCA best care practices from the bystander response through to the in-hospital phase have been associated with improved patient outcomes. This Canadian Cardiovascular Society position statement was developed to provide comprehensive yet practical recommendations to guide the in-hospital care of OHCA patients. Using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system recommendations have been generated. Recommendations on initial care delivery on the basis of presenting rhythm, appropriate use of targeted temperature management, postarrest angiography, and revascularization in the initial phase of care of the OHCA patient are detailed within this statement. In addition, further description of best practices on sedation, use of neuromuscular blockade, oxygenation targets, hemodynamic monitoring, and blood product transfusion triggers in the critical care environment are contained in this document. Last, discussion of optimal care systems for the OHCA patient is provided. These guidelines aim to serve as a practical guide to optimize the in-hospital care of survivors of cardiac arrest and encourage the adoption of "best practice" protocols and treatment pathways. Emphasis is placed on integrating these aspects of in-hospital care as part of a postarrest "care bundle." It is hoped that this position statement can assist all medical professionals who treat survivors of cardiac arrest.

The nonpeptide GP IIb/IIIa antagonist lamifiban protected patients with unstable angina from severe ischemic events during a 3- to 5-day infusion and reduced the incidence of death and infarction at 1 month, suggesting considerable promise for this new therapeutic approach.