73/Wide complex rhythm causing progressive mitral regurgitation in a neonate: is it preexcitation or accelerated idioventricular rhythm?

An 11-day old female with no known risk factors for arrhythmias was noted to have ectopic beats postnatally. Subsequent electrocardiogram demonstrated an intermittent regular broad QRS complex rhythm at the same speed as the preceding sinus beats which resembled pre- excitation. Besides a small patent foramen ovale, initial echocardiogram showed normal cardiac morphology and function. Although the neonate remained asymptomatic throughout, pharmacological treatment with flecainide was commenced in view of sustained arrhythmia and progressive mitral regurgitation. Close review of the 12 lead ECG revealed isorhythmic dissociation which led to the diagnosis of accelerated idioventricular rhythm. In addition to increasing flecainide dosage, initiation of propranolol was required to achieve satisfactory rate control owing to incessant arrhythmia. This combination treatment was well tolerated and achieved successful control of the neonate’s arrhythmia with improvement in mitral regurgitation and cardiac function.