Effect of Ticagrelor on Adenosine-Induced Coronary Flow Reserve in Patients With Microvascular Angina

Inclusion Criteria: For inclusion in the study subjects should fulfill the following criteria: 1. Provision of informed consent prior to any study specific procedures 2. Female or male aged 18-80 years 3. A diagnosis of stable primary MVA based on the presence of * a history of typical effort angina, * exercise-induced ST-segment depression\>1 mm, * normal or near-normal (coronary artery stenosis\<50%) coronary angiography, * absence vasospastic angina * a coronary flow reserve (CFR) \<2.5 in the left anterior descending coronary artery as assessed by coronary blood flow (CBF) response to adenosine at transthoracic Doppler echocardiography * suboptimal control of symptoms on conventional anti-ischemic therapy, as indicated by the occurrence of \>1 episode per week of angina Exclusion Criteria: ubjects should not enter the study if any of the following exclusion criteria are fulfilled: 1. concomitance with any of the cardiac condition below * significant （\>50%）coronary plaque disease * coronary artery spasm at angiography or other evidence of vasospastic angina * valvular or other structural heart disease * uncontrolled hypertension * abnormal echocardiographic examination including left ventricular hypertrophy 2. no previous consumption of the ticagrelor 3. no apparent contraindications to ticagrelor administration. * History of Intracranial Hemorrhage * Active Bleeding * Severe Hepatic Impairment: AST and ALT are greater than 3 times of the upper limit. Bilirubin is greater than the upper limit. * hypersensitivity (e.g. angioedema) to ticagrelor or any component of the product * severe COPD or asthma