Antiarrhythmic Drugs

The Atrial Fibrillation Follow-up Investigation of Rhythm Management trial (2002) randomized over 4,000 patients — mostly older with high stroke risk — to rate control versus rhythm control. There was no difference in overall mortality at five years. Rhythm control was associated with more hospitalizations and drug adverse effects. The key lesson: the drugs available at the time for rhythm control carried enough toxicity and limitations to offset any benefit from restoring sinus rhythm.

The Rate Control versus Electrical Cardioversion trial (2002) similarly showed non-inferiority of rate control for a composite of cardiovascular outcomes in patients with persistent atrial fibrillation. Together with the Atrial Fibrillation Follow-up Investigation of Rhythm Management trial, it established rate control as a reasonable default strategy for many patients.

The Early Rhythm Control in Atrial Fibrillation trial (2020) reframed the question by focusing on newly diagnosed atrial fibrillation. Patients diagnosed within the preceding year who received early rhythm control — with either antiarrhythmic drugs or catheter ablation — had fewer cardiovascular events including death, stroke, and heart failure hospitalizations compared to those managed with usual care. The mechanism is that early rhythm control, initiated before sustained atrial remodeling becomes irreversible, prevents the structural and electrical changes that make atrial fibrillation self-perpetuating.

Rate control alone is reasonable for older patients with minimal symptoms, long-standing persistent atrial fibrillation where remodeling is established, and patients at high risk from antiarrhythmic drug toxicity. The target resting heart rate for rate control is below 110 beats per minute as an initial goal, with tighter control pursued in symptomatic patients.

Rhythm control is preferred — and increasingly favored early — for patients with significant symptoms despite adequate rate control, newly diagnosed atrial fibrillation (within the past year, consistent with the Early Rhythm Control in Atrial Fibrillation trial finding), atrial fibrillation-induced cardiomyopathy (where rhythm control may reverse left ventricular dysfunction), and younger patients where long-term maintenance of sinus rhythm is feasible. Patient preference, after informed discussion of the options and their realistic success rates, is a valid driver of this decision in either direction.

In patients without structural heart disease, the full range of rhythm control agents is pharmacologically available. Flecainide and propafenone are first-line choices for younger patients with high symptom burden — they are highly effective for paroxysmal atrial fibrillation and require a concurrent atrioventricular nodal blocking agent to prevent 1:1 atrial flutter conduction. Sotalol is an alternative with combined rate-slowing and rhythm control properties but requires corrected QT interval monitoring and in-hospital initiation. Dronedarone is acceptable in paroxysmal or persistent atrial fibrillation with preserved ejection fraction. Amiodarone is the most effective agent but reserved for refractory cases due to its cumulative toxicity burden.

Flecainide and propafenone are contraindicated — the Cardiac Arrhythmia Suppression Trial established that Class Ic agents increase mortality in patients with structural heart disease from prior myocardial infarction. Sotalol, dofetilide, and amiodarone are the agents of choice. Dronedarone is acceptable if ejection fraction is preserved and there has been no recent heart failure hospitalization.

This is the most pharmacologically restricted population. Only amiodarone and dofetilide have demonstrated safety — both have trial evidence showing they do not increase mortality in patients with reduced ejection fraction. Flecainide, propafenone, sotalol, and dronedarone are all contraindicated or carry mortality signals in this population. Catheter ablation is increasingly preferred as first-line rhythm control for symptomatic atrial fibrillation with heart failure with reduced ejection fraction.

Class Ic agents are relatively contraindicated in significant left ventricular hypertrophy (wall thickness greater than 1.4 centimeters) because altered conduction and interstitial fibrosis create a proarrhythmic substrate. Amiodarone is the preferred agent. Sotalol and dofetilide are alternatives depending on corrected QT interval and renal function.

Atrial fibrillation of definite onset within the preceding 48 hours carries low immediate thromboembolic risk — there has been insufficient time for left atrial appendage thrombus to form and organize. In this window, cardioversion may proceed after initiating anticoagulation without requiring weeks of pre-cardioversion treatment.

However, post-cardioversion anticoagulation for at least four weeks is mandatory regardless of the CHA2DS2-VASc score, because of atrial stunning — a state of mechanical dysfunction that persists in the left atrium after cardioversion even when sinus rhythm has been electrically restored. During this period, the atrium contracts ineffectively and thromboembolic risk remains elevated until mechanical function fully recovers.

When atrial fibrillation duration exceeds 48 hours or is unknown, two strategies are accepted before cardioversion. The first is delayed cardioversion after at least three weeks of therapeutic anticoagulation, followed by at least four weeks post-cardioversion. The second is early cardioversion guided by transesophageal echocardiography to exclude left atrial appendage thrombus, allowing prompt cardioversion under concurrent anticoagulation without the three-week wait, followed by at least four weeks post-cardioversion. The four-week post-cardioversion anticoagulation period is required for both strategies because of atrial stunning.

The decision to continue anticoagulation beyond the mandatory four weeks depends on ongoing stroke risk, assessed using the CHA2DS2-VASc score. The score assigns points for: congestive heart failure or reduced left ventricular function, hypertension, age 75 or older (two points), diabetes mellitus, prior stroke or transient ischemic attack (two points), vascular disease, age 65 to 74, and female sex. Higher scores correspond to higher annual stroke risk.

Current guidelines recommend anticoagulation for men with a score of two or more and women with a score of three or more (the female sex point alone does not meet the treatment threshold). Direct oral anticoagulants — apixaban, rivaroxaban, dabigatran, and edoxaban — are preferred over warfarin for most patients with non-valvular atrial fibrillation because of superior or equivalent efficacy with lower bleeding risk in large randomized trials. Warfarin remains indicated for valvular atrial fibrillation (mechanical prosthetic valves, moderate-to-severe mitral stenosis) and in patients with severe renal impairment or other direct oral anticoagulant contraindications.