How does structural heart disease affect the choice of antiarrhythmic therapy?

• A. Structural heart disease does not influence antiarrhythmic therapy choice.
• B. Class IC agents are preferred in structural heart disease.
• C. Dofetilide should always be avoided in structural disease.
• D. Amiodarone or dofetilide should be preferred over class IC agents; avoid class IC in structural disease.

Answer: (D)

Structural heart disease changes the risk profile of antiarrhythmic drugs. In the damaged or scarred myocardium, drugs that strongly slow conduction, such as Class IC sodium channel blockers (flecainide, propafenone), can trigger dangerous ventricular proarrhythmias and even increase mortality, a finding highlighted by the CAST experience. Because of this, Class IC agents are avoided in people with structural heart disease.

In contrast, amiodarone and dofetilide (Class III) retain antiarrhythmic efficacy in atrial fibrillation while carrying a lower risk of proarrhythmia in this setting. Amiodarone has broad activity and is effective in patients with LV dysfunction or structural heart disease, though it comes with long-term toxicity considerations. Dofetilide is effective but requires careful inpatient initiation with QT monitoring due to the risk of torsades de pointes.

Thus, when structural heart disease is present, the preferred approach is to use amiodarone or dofetilide rather than a Class IC agent, avoiding Class IC in structural disease.