The purpose of this study is to determine whether Aspirin or Clopidogrel are effective in the prevention of venous obstruction after implantation of cardiac pacemaker or defibrillator.

There are growing numbers of endocardial permanent pacemakers (PPM) and implantable cardioverter defibrillators (ICD) and cardiac resynchronization therapy (CRT) device. Asymptomatic obstruction of the access vein reported to have a high incidence (30-50%) in some studies. This complication can cause some difficulties in follow up procedures such as device upgrading. The purpose of this study is to determine whether Aspirin or Clopidogrel are effective in the prevention of venous obstruction after implantation of cardiac pacemaker or defibrillator.

Inclusion Criteria:

• patients who referred for first implantation of pacemaker, implantable cardiac defibrillator, or cardiac re synchronization therapy device

Exclusion Criteria:

• history of malignancy
• history of coagulopathy or platelet disorder
• history of venous thromboembolism
• history of gastrointestinal hemorrhage or active gastroduodenal ulcer in past 6 months
• history of chronic kidney disorder or serum creatinine more than 1.5 mg/dl
• patients who are on anticoagulant or other antithrombotic drugs or who must be on dual antiplatelet therapy.