Efficacy of a pure Ikr blockade with nifekalant in refractory neonatal congenital junctional ectopic tachycardia and careful attention to damaging the atrioventricular conduction during the radiofrequency catheter ablation in infancy

Junctional ectopic tachycardia (JET)

Junctional ectopic tachycardia (JET) is a tachyarrhythmia arising from the atrioventricular node and His bundle area. Enhanced normal automaticity has been postulated as the mechanism of JET in the majority of patients. It is more common in children and can be seen as congenital or in postoperative settings. It is often a narrow complex tachycardia but can present as a wide complex tachycardia as a result of aberrant conduction. Its differentiation from other arrhythmias especially atrioventricular nodal reentrant tachycardia (AVNRT) can be challenging. Medical treatment of JET is difficult, and catheter ablation remains the mainstay of treatment in refractory cases with a high risk of atrioventricular block and recurrence.

Junctional ectopic tachycardia in infants and children

Tachyarrhythmias originating in the atrioventricular (AV) node and AV junction including the bundle of His complex (BH) are called junctional tachycardia (JT) or junctional ectopic tachycardia (JET). Congenital JET (CJET) is a rare arrhythmia that occurs in patients without a preceding cardiac surgery and can be refractory to medical therapy and associated with high morbidity and mortality. CJET has a high rate of morbidity and mortality with death occurring in 35% of cases. JET occurring within 72 hours after cardiac surgery is referred to as postoperative JET (POJET) and caused by direct trauma, ischemic, or stretch injury to the AV conduction tissues during surgical repair of congenital heart defects. Focal junctional tachycardia (FJT) is also known as automatic junctional tachycardia and includes paroxysmal or non-paroxysmal forms. We discuss a staged approach to therapy with improved pharmacological therapies and the use of catheter-based therapies.

Usefulness of an IKr blocker for ablation of non-pulmonary vein ectopies that are unmappable due to easily initiated atrial fibrillation

PURPOSE

When atrial fibrillation (AF) is initiated by a single or several non-pulmonary vein (PV) trigger ectopic beats, mapping the ectopy is often difficult, requiring a number of electrical cardioversion applications. Nifekalant is a rapidly activating delayed rectifier potassium channel (I_Kr) blocker which may suppress AF initiation without inhibiting ectopy development, thereby allowing the target ectopy to be mapped. To assess the efficacy of nifekalant in the ablation of non-PV ectopies that are unmappable due to easily initiated AF.

METHODS

Eleven consecutive patients were administered nifekalant to map a non-PV ectopy that was unmappable using a conventional method due to easily initiated AF. Nifekalant was intravenously administered as a bolus dose of 0.2 mg/kg, and electrical cardioversion was delivered. Additional boluses of 0.2 mg/kg were repeatedly administered until AF initiation was prevented or until the appearance of significant prolongation of QT interval.

RESULTS

AF suppression without inhibition of ectopy development was achieved in 7 patients. These patients had a higher rate of acute elimination of the ectopy than the remaining 4 patients without AF suppression (7 [100%] vs. 1 [25%] patients, p = 0.024). In addition, patients with suppression of AF initiation had a higher AF recurrence-free rate than those without (7 [100%] vs. 1 [25%] patients, p = 0.024).

CONCLUSION

Nifekalant administration appears useful in the ablation of non-PV ectopies that easily initiate AF.