Proarrhythmia

Proarrhythmia is a new or more frequent occurrence of pre-existing arrhythmias, paradoxically precipitated by antiarrhythmic therapy, which means it is a side effect associated with the administration of some existing antiarrhythmic drugs, as well as drugs for other indications. In other words, it is a tendency of antiarrhythmic drugs to facilitate emergence of new arrhythmias.

Types of proarrhythmia

According to the Vaughan Williams classification (VW) of antiarrhythmic drugs, there are 3 main types of Proarrhythmia during treatment with various antiarrhythmic drugs for Atrial Fibrillation or Atrial flutter:

Ventricular proarrhythmia

• Torsades de pointes (VW type IA and type III drugs)
• Sustained monomorphic ventricular tachycardia (usually VW type IC drugs)
• Sustained polymorphic ventricular tachycardia/ventricular fibrillation without long QT (VW types IA, IC, and III drugs)

Atrial proarrhythmia

• Conversion of atrial fibrillation to flutter (usually VW type IC drugs or amiodarone). May be a desired effect.
• Increase of defibrillation threshold (a potential problem with VW type IC drugs)
• Provocation of recurrence (probably VW types IA, IC and III drugs). It is rare.

Abnormalities of conduction or impulse formation

• Sinus node dysfunction, atrioventricular block (almost all drugs)
• Accelerate conduction over accessory pathway (digoxin, intravenous verapamil, or diltiazem)
• Acceleration of ventricular rate during atrial fibrillation (VW type IA and type IC drugs).

Increased risk

• Presence of structural heart disease, especially LV systolic dysfunction.
• Class IC agents.
• Increased age.
• Females.

Clinical pointers

Class IA drugs

• Dose independent, occurring at normal levels.
• Follow QT interval, keep ms.

Class IC drugs

• May be provoked by increased heart rate.
• Exercise stress tests after loading.

Class III drugs

• Dose dependent.
• Follow bradycardia, prolonged QT closely.