Flecainide-Induced Left Bundle Branch Block.

Flecainide is the first-line antiarrhythmic agent used in patients without structural heart disease. It is a class IC antiarrhythmic drug that inhibits inward sodium current through its dose-dependent blockade of voltage-gated calcium channels within the cardiac membrane. It has been shown to slow the conduction in the left bundle branch block. Unmonitored toxicity can cause ventricular dyssynchrony or fatal arrhythmia. We present a case in which flecainide use caused a new left bundle branch block (LBBB).