Suspected pro‐arrhythmic effects of flecainide and the limitations of in‐hospital short‐duration electrocardiography in detecting ventricular arrhythmia burden in a dog with dilated cardiomyopathy

Abstract A 10‐year‐old, female, spayed Pitbull mix presented for evaluation of an arrhythmia. Echocardiography revealed enlargement of all cardiac chambers and decreased left ventricular systolic function. Electrocardiography demonstrated isolated, ventricular premature complexes. The dog was diagnosed with dilated cardiomyopathy and started on oral pimobendan. Forty‐eight‐hour Holter monitor at this time demonstrated a 2% total ventricular arrhythmia burden, with ventricular couplets and triplets but without ventricular tachycardia. Evidence of complex ventricular ectopy (triplets and couplets) prompted the start of oral flecainide. Recheck in‐hospital echocardiography 6 weeks later demonstrated a normal sinus rhythm. However, recheck Holter demonstrated increased ventricular arrhythmia complexity with runs of ventricular tachycardia. Flecainide was discontinued, and oral sotalol was started. Recheck Holter 4 weeks later revealed a reduction in ventricular arrhythmia burden and no episodes of ventricular tachycardia. This report demonstrates the possible pro‐arrhythmic potential of flecainide and the inaccuracy of in‐hospital, short‐term echocardiographies to determine arrhythmia burden in dogs.