Ibutilide: what's clinically proven, what's being investigated?

Ibutilide is a class III antiarrhythmic drug used intravenously for the chemical cardioversion of atrial fibrillation (AF) and atrial flutter (AFL). It mainly acts by blocking the rapid component (I_kr) of delayed rectifier K⁺ channels, resulting in prolongation of action potential duration in the atrium. Ibutilide fumarate is a methanesulfonamide derivative that is structurally similar to sotalol without the β-adrenoreceptor blocking activity. The success rate of cardioversion of atrial flutter with ibutilide is in the range of 50-70%, whereas its efficacy for the conversion of atrial fibrillation is 30-50%. As compared to ibutilide monotherapy, coadministration with propafenone has a significantly higher success rate of AF termination. Ibutilide is also effective in pre-excited AF by reducing the risk of AF related ventricular tachycardia and thereby reducing the risk of sudden cardiac death. It is a safe drug to use for cardioversion in patients on chronic amiodarone therapy. The main side effect of dofetilide is torsade de pointes (tdp), which occurs in 4% patients, and monomorphic ventricular tachycardia, which occurs in 4.9% patients. Proadministration of magnesium reduces the risk of torsade de pointes. Patients should be monitored for at least 4 h for tdp. Targeting complex fractionated electrograms with the assistance of an ibutilide infusion during catheter ablation of persistent AF has shown mixed results. Conversion rate with an ibutilide infusion is only 30% in the presence of an enlarged left atrium (>5 cm) and 37.7% in the presence of mitral valve disease (MVD), whereas the conversion rate was 82.5% in the absence of MVD and 85% in the absence of both an enlarged left atrium and mitral valve disease (p = <0.001). Ibutilide can be used effectively in patients who are not a candidate for direct current cardioversion or who chose not to undergo electric cardioversion.