Flecainide toxicity in a preterm neonate with permanent junctional reciprocating tachycardia

Antiarrhythmic therapy for narrow QRS supraventricular tachyarrhythmias in newborns and infants in the first year of life: Potent tools to be handled with care

Supraventricular tachyarrhythmias pose a significant challenge in neonates and infants, particularly within the first year of life, where prompt and effective management is crucial. By synthesizing available evidence and clinical experience, this review aims to provide a comprehensive overview of antiarrhythmic therapy in this vulnerable population, with a focus on narrow QRS supraventricular tachyarrhythmias. This review examines the current understanding of supraventricular tachyarrhythmia management and discusses the challenges associated with antiarrhythmic therapy in newborns and infants during the critical first year of life, evaluating the efficacy and safety of various antiarrhythmic agents commonly utilized in this population, including dosing considerations, adverse effects, and strategies for acute management and prophylactic long-term antiarrhythmic treatment.

Case report: Use of therapeutic drug monitoring and pharmacogenetic testing as opportunities to individualize care in a case of flecainide toxicity after fetal supraventricular tachycardia

Flecainide is a class IC antiarrhythmic utilized in prophylaxis of refractory paroxysmal supraventricular tachycardias in pediatric populations. Despite being a highly effective agent, its narrow therapeutic index increases the risk of toxicity and proarrhythmic events, including wide-complex tachycardia. In the absence of direct plasma sampling in the fetus to quantitate flecainide systemic concentrations, clinicians typically make drug dosing decisions from maternal plasma concentrations and QRS duration on maternal ECGs. There remains a paucity of standard guidelines and data to inform the timing and frequency of the aforementioned test in pregnancy and timing of flecainide discontinuation prior to childbirth. Flecainide primarily undergoes metabolism via cytochrome P450 (CYP). Given the variance of CYP-mediated metabolism at the level of the individual patient, pharmacogenomics can be considered in patients who present with flecainide toxicity to determine the maternal vs. fetal factors as an etiology for the event. Finally, pharmacogenetic testing can be utilized as an adjunct to guide flecainide dosing decisions, but must be done with caution in neonates <2 weeks of age. This case report highlights utilization of pharmacogenomic testing and therapeutic drug monitoring as adjuncts to guide therapy for a newborn with refractory supraventricular tachycardia, who experienced flecainide toxicity immediately post-partum and was trialed unsuccessfully on multiple alternative antiarrhythmics without rhythm control.

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

Flecainide acetate is a Vaughan-Williams class IC antiarrhythmic drug prescribed for the treatment of supraventricular arrhythmias. It has a narrow therapeutic index and proarrhythmic effects even at therapeutic doses. Flecainide is metabolized by a CYP2D6 enzyme that exhibits polymorphism. In this case report, we present, to our best knowledge, the first case of toxicity contributed by genetic polymorphism in an infant. Our patient with recurrent supraventricular tachycardia was treated with a therapeutic dose of flecainide but developed heart block requiring extracorporeal membrane oxygenation support and subsequent treatment with lipid emulsion therapy. He was found to have supratherapeutic serum flecainide concentration, and gene testing revealed the patient to be an intermediate metabolizer. With this case report, we reinforce the importance of evaluating the CYP2D6 genotype before drug initiation in the neonatal population and recommend regular monitoring of serum flecainide levels and electrocardiograms in these patients.

Rapid Quantitation of Flecainide in Human Plasma for Therapeutic Drug Monitoring Using Liquid Chromatography and Time-of-Flight Mass Spectrometry

BACKGROUND

Measurement of flecainide is useful to optimize dosage and minimize risks of toxicity. Furthermore, there is a need for urgent sample analysis when flecainide is used in transplacental therapy for fetal tachycardia. To this end, we have developed and validated a rapid assay for the measurement of flecainide in human plasma or serum, using a small sample volume (50 µL).

METHODS

After a simple deproteination with zinc sulfate and methanol, prepared samples were injected onto a short (30 mm) analytical column and eluted using a rapid gradient elution. Detection was performed using time-of-flight mass spectrometry. Flecainide was quantified using flecainide-D4 as internal standard, with both compounds extracted from the total ion chromatogram using a ±5 ppm extraction window based on the theoretical m/z values for the protonated ions.

RESULTS

The assay was linear over a putative therapeutic range (100-1500 mcg/L). Between- and within-assay imprecision and accuracy were <4.6% and 94.8%-110.0%, respectively. Matrix effects were minimal and were compensated for by flecainide-D4. There were no effects due to hemolysis or lipemia, and no carryover was apparent. Total analysis time was just 1.2 minutes (72 seconds).

CONCLUSIONS

We have developed and validated a rapid method for the analysis of flecainide. The method is particularly suited for flecainide therapeutic drug monitoring, when analyzing samples from mothers receiving flecainide for the treatment of fetal tachycardia.

Clinical presentation, management, and postnatal outcomes of fetal tachyarrhythmias: A 10-year single-center experience

Background

Limited information is available regarding the prevalence and outcomes of fetal tachyarrhythmias from the developing countries.

Aims

This study aims to report referral patterns, management protocols, and pregnancy outcomes of fetuses with tachyarrhythmias reporting to a single center in South India.

Methods

All fetuses with documented sustained fetal tachyarrhythmia during the study period (2008-2017) were included. Arrhythmia characterization and hemodynamic evaluation were done using fetal echocardiography. Patients were grouped into supraventricular tachycardia (SVT) and atrial flutter (AF) groups. Patient characteristics, transplacental therapy (TPT), pregnancy, and postnatal outcomes were analyzed.

Results

Total of 19 fetuses included; 11 had SVT and 8 AF. Mean gestational age at referral was higher for AF (32.5 ± 3.2 vs. 29.6 ± 3.3 weeks; P = 0.05). Hydrops fetalis was present 8 (42%) fetuses; 4 in each group. TPT was instituted in 18 fetuses; 12 (66.7%) received combination therapy; 4 (21%) received direct fetal therapy. Eighteen fetuses (91%) were born alive with one intrauterine death in a fetus with SVT and severe hydrops. Seven (87.5%) fetuses with hydrops survived. Twelve patients (66.7%) were delivered in sinus rhythm. Six babies (33.3%) had tachycardia at birth requiring anti-arrhythmic therapy. All patients survived the neonatal period. Duration of trans-placental therapy (3.8 + 3.3 vs. 7.3 + 3.4 weeks) was shorter in the AF group.

Conclusions

Aggressive TPT using combination of drugs achieves excellent pregnancy and postnatal outcomes in fetuses with tachyarrhythmia. Early diagnosis and prompt referral before hemodynamic decompensation is critical for ensuring optimal outcomes.