QT interval prolongation and torsade de pointes: Synergistic effect of flecainide and H1 receptor antagonists

A high percentage of patients having atrial fibrillation (AF) presents with paroxysmal AF. Flecainide, the prototypic class Ic anti-arrhythmic drug is the most effective drug to maintain sinus rhythm in this subgroup of patients, though the drug has potential pro-arrhythmic effects. Furthermore, the H1 receptor antagonists are the most commonly prescribed drugs for the symptomatic treatment of pruritus. Despite having low number of adverse effects, the H1 receptor antagonists have cardiotoxic effects. Flecainide and H1 receptor antagonists present arrhythmic complications including QT interval prolongation and torsade de pointes (TdP). The case presented here is a 65-year-old female who was diagnosed of atrial fibrillation and presented with rashes in lower extremities. The patient was treated using flecainide and H1 receptor antagonists (loratadine and hydroxyzine) that prolonged QT interval and induced TdP. The concomitant administration of flecainide and H1 receptor antagonists seems to have a synergistic effect in QT interval prolongation and subsequent TdP. The concurrent administration of H1 receptor antagonists to patients receiving class Ic anti-arrhythmic drugs should be avoided in order to reduce arrhythmic risk in this population.