Here is the design of a clinical trial:

Official Title: Discontinuation of Β-blocker Therapy in Stabilized Patients After Acute Myocardial Infarction: a Multicenter Randomized Noninferiority Trial

Included conditions:
- Myocardial Infarction

Study Armgroups:
- {'label': 'β-blocker discontinuation arm', 'type': 'EXPERIMENTAL', 'description': 'Discontinuation of β-blocker therapy after at least 1 year of β-blocker therapy after acute myocardial infarction', 'interventionNames': ['Drug: Discontinuation of β-blocker']}
- {'label': 'β-blocker maintenance arm', 'type': 'NO_INTERVENTION', 'description': 'Continuation of β-blocker therapy after acute myocardial infarction'}

Interventions:
- {'type': 'DRUG', 'name': 'Discontinuation of β-blocker', 'description': 'Discontinuation of β-blocker after at least 1 year of β-blocker therapy after acute myocardial infarction', 'armGroupLabels': ['β-blocker discontinuation arm']}

Primary Outcomes:
- {'measure': 'Major adverse cardiac events', 'description': 'a composite of all-cause death, myocardial infarction, hospitalization for heart failure', 'timeFrame': '2.5 years after last patient enrollment'}

Please estimate the sample size based on the assumption: 
The study assumes a one-sided type I error of 2.5%, ≥80% power, and a 2% attrition rate.
Sample size calculations
        Originally, we assumed that the recruitment of study patients would occur at a constant rate over 3 years and that study patients would be followed-up with for an additional 2 years after the recruitment of the last patient (median follow-up of 3.5 years; range, 2â5 years). However, the enrolment rate has already exceeded our initial expectations (actual accrual period of 2 years), prompting us to perform a revised sample size calculation. To maintain a median follow-up duration of 3.5 years (range, 2.5â4.5 years), we have decided to extend the follow-up period to 2.5 years after the recruitment of the last patient. According to data from previous Korean nationwide observational studies, the annual incidence of the primary endpoint is estimated to be 3% in the Î²-blocker maintenance group.12 The non-inferiority margin of the HR selected was 1.4. With a sampling ratio of 1:1, we estimated that 2540 patients (1270 per group) would result in â¥80% power at a one-sided type I error of 2.5% and a 2% attrition rate.