Neonatal life-threatening arrhythmia responding to lidocaine, a probable LQTS3.

Intrauterine and neonatal manifestations of congenital long QT syndrome (LQTS) are associated with a high cardiac risk. We present a newborn, with antecedents of intrauterine premature ventricular contractions, showing in his surface electrocardiogram (ECG): a QTc of 0.69 ms, 2:1 atrioventricular block, autolimited episodes of ventricular tachycardia and Torsade de Pointes. Intravenous esmolol therapy was started, being only partially effective. Because of the ECG phenotype, a LQTS3 is suspected, and intravenous lidocaine was started, achieving sinus rhythm, a normal QTc and no new episodes of ventricular tachycardia. Lidocaine was substituted for oral mexiletine, and esmolol for propranolol. During the follow-up the patient has remained asymptomatic under therapy with propranolol and mexiletine.