A female neonate, 13 days old, diagnosed with fetal tachycardia, without registries of tachyarrhythmias after birth and no 12-lead ECG record at delivery, was admitted to the emergency department with incessant supraventricular tachycardia, with a heart rate of 250 beats per minute (bpm) ( Figure 1 ).

Figure 1

At the admission in the intensive care unit, adenosine (0.05 mg/kg) was unsuccessfully administered twice. So, electrical cardioversion was performed (0.5J/kg + 1J/kg), with immediate interruption of the arrhythmia, however with prompt recurrence. During sinus rhythm, it was possible to identify ventricular pre-excitation. Echocardiogram showed a left ventricular ejection fraction (LVEF) of 46%.

Due to hemodynamic instability, orotracheal intubation was performed and dopamine started. Loading dose of amiodarone (5mg/kg) was administered in 40 minutes, followed by a maintenance infusion of 10mg/kg daily. In the following days, the patient evolved with acute kidney failure and hydroelectrolytic disturbance. In this context, the newborn developed severe bradycardia requiring the interruption of the amiodarone infusion and peritoneal dialysis. Thereafter, epinephrine and dobutamine were administered.

Amiodarone was restarted after the correction of the hydroelectrolytic disorders, at a dose of 5 mg/kg/day, with dose progression over the next days, reaching up to 30 mg/kg/day. It was not possible to prescribe other available antiarrhythmic drugs due to the ventricular dysfunction, and to the need of vasoactive drugs. Despite that, the 28-day old infant evolved with incessant AV tachycardia, being then decided to attempt RF ablation.

The electrophysiological study was performed after 8h of fasting and under general anesthesia. A single standard 5 French, 4-millimetre tip deflectable quadripolar catheter (5 FR RF – Medtronic Marinr steerable catheter) was introduced through the left femoral vein for mapping and ablation purposes. Tachycardia was interrupted during programmed stimulation and revealed a left posterior accessory-pathway pre-excitation pattern on the surface EKG ( Figure 2 ). The foramen ovale was used for left atrium access ( Figure 3 ). After administration of 100 units per kilogram of intravenous heparin, RF application was successfully delivered at the targeted site, with immediate conduction block through the accessory pathway ( Figure 4 ). RF application was maintained for one minute with 30W. There were no intra-procedural complications. Right bundle branch block occurred due to mechanical trauma with spontaneous recovery.

Figure 2

Figure 3

Figure 4

During the following hours, the hemodynamic condition improved markedly. The neonate was extubated and inotropic drugs were discontinued after 72h. Patient was discharged 6 days later. No more tachycardias or pre-excitation recurrence have been registered so far. The child remains with no arrhythmias, without pharmacological treatment, 6 years after the procedure. EKG shows sinus rhythm and Echocardiogram has normal ventricular function without segmental lesions.

The incidence of tachycardias in the neonatal period is between 1% and 5%.^{1 , 2} AVRT and atrial flutter account for 90% of the fetal and neonatal tachyarrhythmias.³ In most of these cases pharmacological and eventually electrical cardioversion may be sufficient to obtain satisfactory clinical control. When the arrhythmia recurs, its frequency decreases in the first year of life (90% of patients), and invasive interventions are rarely needed.⁴

It is important to take into account that supraventricular tachycardia may be unrecognized in newborns until heart failure (HF) symptoms emerge; thus, neonates may present a decrease in LV function, or even cardiogenic shock if the correct diagnosis is not given.⁵ In this case, despite the diagnosis of fetal tachycardia, an adequate investigation was not performed after birth, and the newborn was discharged without EKG. The SVT diagnosis was only obtained on the 13th day of life, when the child was taken to the emergency room in the context of cardiogenic shock.

To prevent recurrence, antiarrhythmic prophylaxis is recommended during the first year of life. Digoxin or propranolol are generally considered as the initial antiarrhythmic therapy for concealed accessory pathways. In case of first-line drugs failure, class IA (quinidine), class IC (flecainide), or class III (amiodarone or sotalol) drugs can be considered. In manifest accessory pathways, oral propafenone is reasonable for ongoing management in patients without structural or ischemic heart diseases. Oral amiodarone may be considered in patients with AVRT in whom propafenone is ineffective or contraindicated.⁶

The first reports demonstrating safety and efficacy of RF ablation in children were published by the Pediatric Electrophysiology Society in 1994.¹ In recent periods, publications have shown an evolution in the success rate and a decrease in the number of complications.^{7 - 15}

According to the 2016 HRS SVT guideline, ablation is recommended for documented SVT, recurrent or persistent, when medical therapy is either not effective or is associated with intolerable adverse effects. One must take into account that for very young children, the threshold for ineffectiveness and intolerability should be higher.

Death and major complications are rare, usually related to underlying heart diseases, lower patient weight, greater number of RF applications, and left-sided procedures.¹

In general, radiofrequency ablation in small infants (less than 5 kg and younger than 6 months of age) should be reserved for life threatening, or refractory arrhythmias, such as the presented case.^{1 , 6}

In conclusion, systematic investigation and a close follow-up is needed in newborns diagnosed with fetal tachycardia. In specific cases, radiofrequency ablation should be considered as the therapeutic approach, having in mind the greater risks of complications in this population.