Here is the design of a clinical trial:

Official Title: Aspirin Discontinuation After Left Atrial Appendage Occlusion in Atrial Fibrillation

Included conditions:
- Atrial Fibrillation
- Stroke
- Bleeding

Study Armgroups:
- {'label': 'Aspirin group', 'type': 'EXPERIMENTAL', 'description': 'Study patients assigned to Aspirin group will receive enteric coated aspirin (100 mg/day).', 'interventionNames': ['Drug: Aspirin Tablet']}
- {'label': 'Control group', 'type': 'PLACEBO_COMPARATOR', 'description': 'Study patients assigned to control group will receive placebo.', 'interventionNames': ['Drug: Placebo']}

Interventions:
- {'type': 'DRUG', 'name': 'Aspirin Tablet', 'description': 'Aspirin 100mg qd', 'armGroupLabels': ['Aspirin group']}
- {'type': 'DRUG', 'name': 'Placebo', 'description': 'Placebo qd', 'armGroupLabels': ['Control group']}

Primary Outcomes:
- {'measure': 'Number of Participants with stroke', 'description': 'A stroke is a medical condition in which poor blood flow to the brain results in cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. They result in part of the brain not functioning properly. Signs and symptoms of a stroke may include an inability to move or feel on one side of the body, problems understanding or speaking, dizziness, or loss of vision to one side. If symptoms last less than one or two hours it is known as a transient ischemic attack (TIA) or mini-stroke. A hemorrhagic stroke may also be associated with a severe headache. The symptoms of a stroke can be permanent. Brain computed tomography or MRI may help diagnose stroke.', 'timeFrame': '24 months after the date of randomization.'}
- {'measure': 'Number of participants with systemic embolism', 'description': 'An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus is usually a blood clot (thrombus). An embolism can cause partial or total blockage of blood flow in the affected vessel.\n\nAn embolism in which the embolus is a piece of thrombus is called a thromboembolism.\n\nAn embolism is usually a pathological event, i.e., accompanying illness or injury. Sometimes it is created intentionally for a therapeutic reason, such as to stop bleeding or to kill a cancerous tumor by stopping its blood supply.\n\nEmbolism can be classified as to where it enters the circulation either in arteries or in veins. Arterial embolism are those that follow and, if not dissolved on the way, lodge in a more distal part of the systemic circulation.', 'timeFrame': '24 months after the date of randomization.'}
- {'measure': 'Number of participants with cardiovascular/unexplained death', 'description': 'Cardiovascular deaths refer to deaths due to heart dysfunction, injury of cardiac structure, coronary artery diseases and lethal arrhythmias or sudden death that cannot be explain. Cardiovascular deaths can be diagnosed with clinical symptoms or from the results of diagnostic examinations.', 'timeFrame': '24 months after the date of randomization.'}
- {'measure': 'Number of participants with major bleedings', 'description': 'Major bleedings refer to the heavy bleedings of the mains organs of the body, usually include intracranial bleeding and gastrointestinal bleeding et al.. Brain computed tomography and gastrointestinal endoscope are the common approaches for diagnosing major bleedings.', 'timeFrame': '24 months after the date of randomization.'}
- {'measure': 'Number of participants with acute coronary syndrome', 'description': 'Acute coronary syndrome is a syndrome (set of signs and symptoms) due to decreased blood flow in the coronary arteries such that part of the heart muscle is unable to function properly or dies. The most common symptom is chest pain, often radiating to the left shoulder or angle of the jaw, crushing, central and associated with nausea and sweating. Many people with acute coronary syndromes present with symptoms other than chest pain, particularly, women, older patients, and patients with diabetes mellitus.\n\nAcute coronary syndrome is commonly associated with three clinical manifestations, named according to the appearance of the electrocardiogram (ECG): ST elevation myocardial infarction (STEMI, 30%), non-ST elevation myocardial infarction (NSTEMI, 25%), or unstable angina (38%). There can be some variation as to which forms of myocardial infarction (MI) are classified under acute coronary syndrome.', 'timeFrame': '24 months after the date of randomization.'}
- {'measure': 'Number of participants with coronary or periphery artery disease requiring revascularization', 'description': 'Conronary or periphery artery diseases, regardless stable or not, need revascularization by stent which require long-term aspirin therapy', 'timeFrame': '24 months after the date of randomization.'}

Please estimate the sample size based on the assumption: 
The study assumes a power of 0.8, a one-sided alpha of 0.025, and a 10% attrition rate.
Sample size justification
        The statistical objective is to determine if the control group is non-inferior to the aspirin group with respect to the event rate for the composite endpoints. The reasons for the non-inferiority design are as follows. First, aspirin, as one of the most widely used drugs, serves as a standard treatment. Second, if placebo is non-inferior to aspirin, discontinuation of aspirin post LAAO will be of high cost effectiveness and may improve quality of life if not on medication. Also, testing the non-inferiority hypothesis requires smaller sample size.
        Event rate is defined as the expected number of events per 100 patient years of follow-up. The study event rate is the combination of event rates from both the aspirin and placebo arms. The estimated event rates for this trial were established based on the rates seen in the LAAO arm of previous Watchman studies and the aspirin arm of previous aspirin trials.13 14 16â18 20 30â33 In the EWOLUTION study, the rates of stroke, major bleeding and cardiovascular death were 1.3%, 2.7% and 2.25%, respectively.17 In the ASCEND (A Study of Cardiovascular Events iN Diabetes) trial, the rates of myocardial infarction and vascular diseases requiring revascularisation were approximately 0.9%.32 Therefore, we conservatively estimate a combined rate for the primary endpoint of 7 events per 100 patient-years. A risk ratio criterion (control group over aspirin group) of 1.5 will be used to establish non-inferiority with a power of 0.8. Therefore, 191 events are required to be observed based on one-sided alpha of 0.025. The subject recruitment is assumed to be over a 2-year period and all subjects will be followed up until 2 years after the last recruitment. Given these assumptions, the sample size of the ASPIRIN LAAO trial is calculated as 1120 subjects, considering a 10% attrition rate. The attrition rate is estimated according to our follow-up data of a previous registry regarding Watchman device implantation (ClinicalTrials.gov: NCT03788941). Achieving adequate participant enrollment to reach target sample size should be feasible within the 2-year recruitment period due to the large operation volume of the participating centres. To further facilitate the recruitment of patients, advertisement of this study will be exhibited by posters in the wards and outpatient clinics.