**1. Introduction**

An important and integral part of an optimal medicament therapy for patients with CAD in an acute as well as in a stable, chronic phase of the disease is antiplatelet therapy. The estimated number of patients requiring DAPT, consisting of a combination of ASA and an oral inhibitor of the platelet P2Y12 receptor for adenosine 5′-diphosphate (ADP), is considerable and has increased over time all around the world. Based on population estimates from 2015, in Europe 1.4–2.2 million patients per year may have an indication for DAPT after coronary intervention or myocardial infarction (MI), respectively [1]. There is, however, confusion about the optimal type and duration of DAPT in patients with established CAD,

undergoing coronary revascularization or not. This derives from apparently conflicting results given in the available studies and limited evidence on various patient subsets [1]. Depending on the disease stage (ACS with PCI, CCS or coronary surgical revascularization), and comorbidity of each patient (e.g., atrial fibrillation, left ventricular thrombus, etc.), the strategy of antiplatelet/ anticoagulant therapy is altered (combination of drugs, dosing, and duration of therapy). In patients with ACS treated with coronary stent implantation, DAPT is recommended for 12 months (preferring ticagrelor combined with ASA) [1]. In a patient with stable CAD treated with coronary stent implantation, DAPT consisting of clopidogrel in addition to aspirin is recommended for 6 months irrespective of the stent type (Class I, level of evidence A), and DAPT up to 12 months may be reasonable (Class IIb, level of evidence A) [1]. If treated with drug-coated balloon, DAPT (aspirin plus clopidogrel) should be considered for 6 months (Class IIa, level of evidence B) and prolonged up to 12 months in tolerant patients without bleeding complications [1]. As opposite, guidelines and especially clinical practice are not uniform and specific regarding patients who will undergo CABG. Latest guidelines regarding DAPT after CABG give general recommendation for duration and choice of antiplatelet therapy with relatively strong class of recommendation I or IIa/IIb1 . Still, level of evidence in recommendations is mostly C or B2 which points out that the foundation of recommendations is based on expert opinion and not on multiple RCTs or meta-analyses [1].

This chapter will give an overview of antiplatelet drugs, their mechanism of action, possible resistance to antiplatelet drugs, and clinical significance of resistance to antiplatelet drugs. Also, it will give an overview of literature regarding duration and choice of antiplatelet therapy after CABG in setting of ACS or CCS.
