Stepwise Strategy for Treatment of Atrialfibrillation Substrate Study

Inclusion Criteria: Aged 18-80 years, with persistent atrial fibrillation complicated by left atrial enlargement (left atrial anteroposterior diameter 40-50mm); Having the willingness to undergo atrial fibrillation cardioversion and planned to receive amiodarone for pharmacological cardioversion; Having signed a written informed consent form for participation in the study; Not concurrently participating in any other interventional studies. Exclusion Criteria: Females who are pregnant, lactating, or planning to have children within the next 2 years; Patients whose arrhythmia fails to convert to sinus rhythm with medication and who refuse electrical cardioversion; Patients whose arrhythmia cannot be converted to sinus rhythm with either medication or electrical cardioversion; Glomerular filtration rate (eGFR) \< 30 ml/min/1.73m² (calculated by the CKD-EPI formula); Patients with biliary cirrhosis or cholestasis; Hyperthyroidism; A history of bradycardia (heart rate \< 50 beats/min) or atrioventricular block of second degree or higher; Sick sinus syndrome; Known allergy to iodine, amiodarone, or any of its excipients; Concomitant use of other drugs that prolong the QT interval, or a history of torsades de pointes; Contraindications to atrial fibrillation cardioversion, such as cardiac thrombosis or contraindications to anticoagulation; A history or current presence of the following diseases or conditions: 1. Moderate to severe rheumatic heart disease, valvular heart disease; a history of atrial-related surgery, including valve replacement, radiofrequency ablation for atrial fibrillation/atrial tachycardia/atrial flutter, atrial septal defect occlusion, or complex congenital heart disease surgery; 2. A history of myocardial infarction, unstable angina, syncope, or cerebrovascular accident within 3 months; 3. NYHA Class III-IV congestive heart failure or EF \< 40%; 4. Patients judged by the investigator to have poor compliance, inability to complete the study as required, or an expected lifespan of less than 1 year.