A case of neonatal single twin flecainide toxicity after therapeutic in utero exposure for fetal SVT

Abstract

A case of neonatal single twin flecainide toxicity after therapeutic in utero exposure for fetal SVT, Toxicology Communications, 1:1, 41-44, ABSTRACTA 9 hour old twin neonate, who was treated with flecainide in utero for fetal supraventricular tachycardia, presented with hypotension and a wide complex tachycardia concerning for flecainide toxicity. The patient was given a bolus of sodium bicarbonate with transient narrowing of her QRS complex. She was then intubated and started on a sodium bicarbonate drip with full resolution of her wide complex tachycardia within 24 hours. Work up showed no evidence for structural cardiac pathology or infection and she did not experience any further arrhythmias after termination of her presenting wide complex tachycardia. The patient was discharged home at 10 days of age and has had no further sequelae. This case report describes a novel presentation of in utero flecainide toxicity and summarizes the therapies available to treat this rare, but potentially lethal, presentation.

Complete Heart Block Secondary to Flecainide Toxicity: Is It Time for CYP2D6 Genotype Testing?

“…Flecainide, a class IC antiarrhythmic drug, works by blocking fast-acting sodium channels to slow down depolarization in myocytes. 7 It is an effective second-line agent for the treatment of refractory SVT in infants, 8 but, in large doses, flecainide can lead to conduction disturbances such as widening of the QRS complex that can escalate into ventricular tachycardia and cardiovascular collapse. 7 Most reported causes of toxicity in infants have been due to dosing errors.…”

“…7 It is an effective second-line agent for the treatment of refractory SVT in infants, 8 but, in large doses, flecainide can lead to conduction disturbances such as widening of the QRS complex that can escalate into ventricular tachycardia and cardiovascular collapse. 7 Most reported causes of toxicity in infants have been due to dosing errors. In our patient, we believe that flecainide toxicity was contributed by reduced metabolism secondary to an unfavorable genetic polymorphism.…”

“…The use of sodium bicarbonate has also been proposed because it can theoretically be used to overcome sodium blockade by displacing flecainide from its receptor sites to reverse the action of sodium channel blockade. 7,25 Alkalinization also converts flecainide to its inactive nonionized form. 7,25 Indeed, in several studies, researchers have reported successful treatment with the use of sodium bicarbonate.…”

“…7,25 Alkalinization also converts flecainide to its inactive nonionized form. 7,25 Indeed, in several studies, researchers have reported successful treatment with the use of sodium bicarbonate. 6,7,25 Our patient was effectively treated with ECMO, which is consistent with other published case reports, 26,27 revealing that ECMO can be an effective means for restoring circulation and allowing drug clearance.…”