Flecainide Safety in Patients With Coronary Artery Disease and Atrial Fibrillation

Inclusion Criteria: * Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures * At least 18 years of age at the time of signing the Informed Consent Form * Non-permanent atrial fibrillation or ectopic atrial tachycardia with rhythm control strategy, documented on any modality in the 1 year preceding the consent date * 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. * LVEF ≥ 45% documented on any imaging modality\* Exclusion Criteria: * LVEF \< 45% * NYHA class III or IV congestive heart failure * Active treatment with amiodarone * History of intolerance of flecainide or both sotalol and amiodarone * Clinically significant uncorrected hypokalemia or hypomagnesemia before initiation of trial treatment. * Evidence or history of thyroid dysfunction contraindicating amiodarone use, where amiodarone would be prescribed as standard of care treatment. * Hypersensitivity to the active substances or any excipients. * Unstable angina or inducible ischemia on exercise stress testing, myocardial perfusion imaging, stress cardiac MRI, or fractional flow reserve performed for clinical indications * Baseline QRS duration ≥ 120 ms, unless a functioning pacemaker is present * Baseline corrected QT interval (Fridericia) ≥ 500 ms * Pre-existing advanced AV block (second-, or third-degree) * Pre-existing sick sinus syndrome or sinus bradycardia \<50 bpm * Known channelopathy * Contra-indication to AV-slowing agents, including beta-blockers, diltiazem or verapamil * Atrial fibrillation due to reversible cause * Active intracardiac thrombus * Acute coronary syndrome during the 3-month period preceding the consent date * 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 * Moderate or severe congenital heart disease as per 2020 ESC guidelines * Hypertrophic cardiomyopathy (septal or posterior wall thickness \>1.5 cm) * Significant chronic kidney disease (eGFR \<40 mL/min) * Life expectancy less than 1 year * 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 * 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. * Participation in an interventional Trial with an investigational medicinal product (IMP) or device