The goal of this clinical trial is to learn whether the antiarrhythmic drug flecainide can be used as safely as standard rhythm-control drugs in people with atrial fibrillation (AF) and stable coronary artery disease (CAD). The study includes adults aged 18 years and older who have AF and known but stable coronary artery disease.

The main questions this study aims to answer are:

• Is treatment with flecainide as safe as standard rhythm-control drugs (sotalol or amiodarone) in this patient group?
• Does flecainide lead to similar or fewer serious side effects, hospitalisations, or deaths compared with standard treatment?

Researchers will compare patients treated with flecainide to patients treated with standard rhythm-control therapy (sotalol or amiodarone) to see whether flecainide is not worse in terms of safety outcomes.

Participants will:

• Be randomly assigned to receive either flecainide or standard rhythm-control medication
• Take the assigned medication as part of routine clinical care
• Attend regular follow-up visits at the hospital and have additional follow-up by telephone
• Undergo routine heart tests such as electrocardiograms and echocardiography
• Complete questionnaires about symptoms, quality of life, and daily functioning

This study follows patients for at least one year and collects information on safety, heart rhythm outcomes, quality of life, and healthcare use.

Inclusion Criteria:

1. Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures

2. At least 18 years of age at the time of signing the Informed Consent Form

3. Non-permanent atrial fibrillation or ectopic atrial tachycardia with rhythm control strategy, documented on any modality in the 1 year preceding the consent date

4. Stable coronary artery disease without argument, defined as:

   1. Prior percutaneous coronary intervention; OR
   2. Prior revascularised ACS or coronary artery bypass surgery > 3 months at enrolment; OR
   3. Invasive coronary angiography demonstrating coronary atherosclerosis, defined as ≥50% diameter stenosis in at least one major epicardial coronary artery; OR
   4. Coronary CT scan showing coronary stenosis CAD-RADS stage ≥ 3 on, including CAD-RADS stages 4 and 5 in the absence of ischemia on exercise testing, myocardial perfusion imaging (MIBI), stress cardiac MRI, or fractional flow reserve.

5. LVEF ≥ 45% documented on any imaging modality*

Exclusion Criteria:

1. LVEF < 45%
2. NYHA class III or IV congestive heart failure
3. Active treatment with amiodarone
4. History of intolerance of flecainide or both sotalol and amiodarone
5. Unstable angina or inducible ischemia on exercise stress testing, myocardial perfusion imaging, stress cardiac MRI, or fractional flow reserve performed for clinical indications
6. Baseline QRS duration ≥ 120 ms, unless a functioning pacemaker is present
7. Baseline corrected QT interval (Fridericia) ≥ 500 ms
8. Pre-existing advanced AV block (second-, or third-degree)
9. Pre-existing sick sinus syndrome or sinus bradycardia <50 bpm
10. Known channelopathy
11. Contra-indication to AV-slowing agents, including beta-blockers, diltiazem or verapamil
12. Atrial fibrillation due to reversible cause
13. Active intracardiac thrombus
14. Acute coronary syndrome during the 3-month period preceding the consent date
15. Cardiac surgery, including coronary artery bypass surgery, during the 3-month period preceding the consent date or planned at a future date at the time of consent
16. Moderate or severe congenital heart disease as per 2020 ESC guidelines
17. Hypertrophic cardiomyopathy (septal or posterior wall thickness >1.5 cm)
18. Significant chronic kidney disease (eGFR <40 mL/min)
19. Life expectancy less than 1 year
20. Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using an adequate, highly effective contraceptive
21. Inability to provide written informed consent, including decision-making incapacity due to cognitive impairment or other medical or psychiatric conditions that preclude adequate understanding of the study and its procedures.
22. Participation in an interventional Trial with an investigational medicinal product (IMP) or device

Starting 12 months after publication

Upon reasonable request to the Principal Investigator