To validate the prognostic importance of the burden of new-onset atrial fibrillation (NOAF) complicating acute myocardial infarction (AMI) in a prospectively designed hospital-based registry. To characterize those factors that contribute to the progression of post-MI NOAF burden. To establish a prediction model for the risk stratification of patients with NOAF complicating AMI. To explore the clinical usefulness of NOAF burden in guiding the anticoagulation therapy among patients with post-MI NOAF.

Our previously designed single-center retrospective cohort study (NCT03533543) suggested that patients with a greater burden of NOAF complicating AMI were challenged by a poor prognosis. In the present study, we aim to design a multicenter, prospective, hospital-based registry to validate the preceding findings. We plan to enroll patients who were admitted for AMI in 9 tertiary medical centers from Shanghai, Henan, and Zhejiang provinces and developed NOAF during the index hospitalization. All eligible patients' demographics, cardiovascular risk factors, comorbidities, laboratory tests, echocardiography data, angiography data, and medications will be collected. NOAF burden is calculated by dividing the total AF duration by the total continuous electronic monitoring (CEM) duration. Other NOAF related characteristics, such as AF pattern, AF frequency, and symptomatic or silent AF, and the longest AF episode duration will also be evaluated. All patients who are discharged alive will be followed for at least 2 years and cardiovascular outcomes will be recorded.

Inclusion Criteria:

• Adult patients (>18 years old);
• Patient with AMI (including STEMI and NSTEMI) who developed NOAF during the index hospitalization;
• Patients must have received in-hospital CEM for at least 5 days;
• Patients must give informed consent.

Exclusion Criteria:

• Patients with a medical history of pre-existing AF;
• Patients with a medical history of rheumatic valvular disease;
• Patients with a medical history of sick sinus syndrome;
• Patients undergoing emergent coronary artery bypass surgery;
• Patients who suffer malignant tumors with an expected lifetime less than 1 year ;
• Patients who refuse to receive CEM during hospitalization and the data of heart rhythm cannot be retrieved;
• Patients who refuse to receive percutaneous coronary intervention (PCI) or have contraindications for PCI;
• Patients who have died during the index hospitalization.

Patients with AMI who do not have a medical history of AF and develop an incident AF episode during the index hospitalization.