Bivalirudin in Elderly Patients Undergoing Elective Percutaneous Coronary Intervention.

Inclusion Criteria: * Age ≥75 years old; * Planned elective PCI for patients with acute coronary syndrome; * Life expectancy ≥ 1 year; * Provide written informed consent. Exclusion Criteria: * Contraindications to angiography or PCI; * Active bleeding or bleeding constitution, bleeding tendency, including GI or urinary tract hemorrhage (3 months), cerebral hemorrhage (6 months) or cerebral infarction history (3 months), etc; * Other disease may lead to vascular lesions and secondary bleeding factors (such as active gastric ulcer, active ulcerative colitis, intra-cerebral mass, aneurysm, etc.); * Severe renal insufficiency (eGFR \< 30 mL/min/ 1.73 m2); * Elevated AST, ALT level higher than three times of the normal upper limit; * Advanced heart failure (NYHA classification grading of cardiac function ≥Ⅲ) Complicated with immune system diseases# * Abnormal hematopoietic system: platelet count \< 100 × 109 / L or \>700 × 109 / L, white blood cell count \< 3×109/L etc; * Suffering from acute infections ,infectious diseases or other serious diseases, such as malignant tumors; * Known intolerance, or contraindication to any antithrombotic medication * Known allergy to the study drugs and instruments (UFH, bivalirudin, aspirin and clopidogrel, stainless steel, contrast agents, etc.), or those allergic constitution. * Non-cardiac co-morbid conditions are present that may result in protocol non-compliance; * Patients who are actively participating in another drug or device investigational study, which have not completed the primary endpoint follow-up period; * Patient's inability to fully cooperate with the study protocol