Review Question - QID 108178

This question examines rhythm control for a patient with persistent atrial fibrillation with no structural heart disease. The best antiarrhythmic for such a patient is a class IC drug, such as flecainide or propafenone.

Class IC antiarrhythmics are the most potent Na+ channel blockers of the class I drugs. They markedly decrease the upstroke of the action potential and conduction velocity in atrial, ventricular, and Purkinje fibers. They were originally developed to treat ventricular arrhythmias, but such use has diminished because studies have shown increased mortality in patients taking class IC drugs for ventricular arrhythmia following cardiac arrest or myocardial infarction. Furthermore, in patients with left ventricular dysfunction, class IC drugs can precipitate heart failure. Thus, class IC drugs should be avoided in patients with underlying heart abnormalities such as coronary artery disease or ventricular dysfunction.

Gutierrez and Blanchard discuss dosing strategies for class IC drugs in the context of atrial fibrillation. Both flecainide and propafenone are well absorbed orally. Noncardiac side effects include CNS-associated effects such as confusion, dizziness, blurred vision and disturbances of taste. The drugs can be taken at the onset of atrial fibrillation with good effect.

The Cardiac Arrhythmia Suppression Trial (CAST) investigators reported early in their observations that flecainide had to be discontinued from further study. It, along with encainide, were associated with markedly increased mortality in patients with ventricular arrhythmia after a myocardial infarction. The results of this trial continue to be incorporated in the American Heart Association guidelines for rhythm control in atrial fibrillation.

Incorrect Answers:
Answer 1: Verapamil is a class IV antiarrhythmic that inhibits L-type Ca2+ channels. It primarily affects AV node conduction, and thus is involved in rate control.
Answer 3: Procainamide is a class IA antiarrhythmic that produces moderate blockade of fast Na+ channels in a use-dependent fashion. Since they prolong repolarization and increase the risk of after-depolarizations (and thus torsades de pointes), its use has declined.
Answer 4: Mexiletine is a class IB antiarrhythmic that also inhibits fast Na+ channels, but it typically shortens the action potential duration and the refractory period. They preferentially act on diseased or ischemic cells. They are used for suppression of ventricular arrhythmias in association with ischemia or digitalis toxicity.
Answer 5: Amiodarone is a class III antiarrhythmic that share mechanisms of action with multiple classes. Clinically, it is a guideline-preferred drug for rhythm control in patients with concurrent atrial fibrillation and structural abnormalities of the heart.