Coronary artery disease (CAD) can be divided into macrovascular and microvascular disease, both different manifestations of atherosclerosis. Macrovascular CAD, i.e. obstructive CAD of epicardial coronary arteries have traditionally been the focus of CAD treatment. Microvascular circulation, on the other hand, consists of arterioles (diameter \<100 μm) within myocardium and abnormalities in this arterial bed may also impair myocardial perfusion and result in ischaemia. An indication of microvascular disease can be achieved with coronary flow reserve (CFR) which is an integrated measure of flow through both large epicardial arteries and coronary microcirculation. CFR measurement is the ratio of resting coronary artery mean diastolic flow velocity in comparison to hyperaemic coronary artery mean diastolic flow velocity, where hyperaemia is often induced with pharmacologic agent such as adenosine infusion. CFR of the left anterior descending (LAD) coronary artery during pharmacologic stress echocardiography has been found to provide effective prognostic information in patients with known or suspected CAD. This seems evident across patient populations, such as those with diabetes or chronic kidney disease, or older age. Particularly, a CFR \<2.0 has been associated with markedly increased cardiovascular (CV) risk in an unselected patient population.
Ticagrelor primary mode of action is as a direct acting reversibly binding P2Y12 antagonist inhibiting ADP-induced platelet activation. However, ticagrelor has also been shown to increase extracellular adenosine concentration by inhibition of the equilibrative nucleoside transporter 1 (ENT1). Adenosine has been described to have a number of physiological effects including vasodilation, anti-inflammation, anti-platelet and cardioprotective effects and ticagrelor has been shown to enhance many of these adenosine-induced effects in animal models and in man. These adenosine-mediated effects may be beneficial to CAD patients and potentially impact coronary microvascular function and contribute to the clinical profile of ticagrelor. So far only one study has explored ticagrelor effect on coronary microvascular function. They showed, by using rubidium 82 positron emission tomography/computed tomography, that ticagrelor could improve local CFR compared to clopidogrel in CAD patients specifically in those regions that before treatment had impaired CFR (\<2.5). CFR has been shown to be a strong independent predictor in diabetic patients with suspected coronary disease for future coronary events and survival.
The ongoing THEMIS study is designed to test the hypothesis that ticagrelor is superior to placebo, in prevention of major CV events, as measured by time to first event of the composite of CV death, MI, or stroke in patients with T2DM at high risk of CV events.
Patients undergoing elective PCI are excluded from the THEMIS study as these patients are treated with clopidogrel plus aspirin. The current study is designed to fill this data gap by generating clinically meaningful data with ticagrelor in THEMIS-like patients undergoing elective PCI.
