Proarrhythmia

Lore & Background

Proarrhythmia is categorized into three main types: ventricular proarrhythmia, atrial proarrhythmia, and abnormalities of conduction or impulse formation. Ventricular proarrhythmia includes torsades de pointes (associated with Vaughan Williams class IA and class III drugs), sustained monomorphic ventricular tachycardia (usually class IC drugs), and sustained polymorphic ventricular tachycardia or ventricular fibrillation without long QT (classes IA, IC, and III drugs). Atrial proarrhythmia involves conversion of atrial fibrillation to flutter (usually class IC drugs or amiodarone), which is generally considered an adverse proarrhythmic effect, not a desired outcome. Other atrial proarrhythmias include increase of defibrillation threshold (a potential problem with class IC drugs) and provocation of recurrence (probably classes IA, IC, and III drugs), which is rare.

Reader's Guide

Proarrhythmia is a significant clinical concept because it highlights the paradoxical risk of antiarrhythmic therapy: drugs intended to suppress arrhythmias can instead provoke new or more frequent arrhythmias. The risk is increased in the presence of structural heart disease, especially left ventricular systolic dysfunction, with class IC agents, increased age, and in females. Clinical pointers vary by drug class: class IA drugs are dose-independent and require QT interval monitoring; class IC drugs may be provoked by increased heart rate and warrant exercise stress tests after loading; class III drugs are dose-dependent and require close monitoring for bradycardia and prolonged QT. Understanding proarrhythmia is essential for safe prescribing and management of patients with atrial fibrillation or flutter, as it guides drug selection and monitoring strategies to minimize adverse outcomes.

Did You Know?

• Proarrhythmia is a side effect paradoxically precipitated by antiarrhythmic therapy.
• Torsades de pointes is a type of ventricular proarrhythmia associated with Vaughan Williams class IA and class III drugs.
• Conversion of atrial fibrillation to flutter is generally considered an adverse proarrhythmic effect of class IC drugs or amiodarone, not a desired effect.
• Increased risk of proarrhythmia is associated with structural heart disease, class IC agents, increased age, and females.