FIG 22.15 Run of permanent junctional reciprocating tachycardia with a typical long RP interval and retrograde atrial activation, which breaks to sinus on the second-to-last beat of the tracing A number of antiarrhythmic medications have been used to treat PJRT, and a single most effective agent has not emerged β-blockers are the common first choice, likely reflecting physician comfort rather than proven efficacy Caution should be exercised when β-blockers are being given to neonates as they may cause hypoglycemia and sleep disturbances; moreover, occasionally infants do not eat as well while on antiarrhythmic medications Complete tachycardia suppression with medications varies from 25% in the recent series to more than 80% in a study using regimens that included amiodarone.74,75 Medical therapy is commonly employed in neonates and infants, whereas older children typically undergo ablation Catheter ablation is the primary treatment for PJRT in older children or small children who fail medical management or have frequent bouts tachycardia with echocardiographic evidence of ventricular dysfunction or clinical signs of heart failure Success rate for catheter ablation of PJRT is 90% (Kang).74 Atrial Flutter in the Newborn Although atrial flutter is uncommon in children with structurally normal hearts, neonatal atrial flutter does occur (Fig 22.16) This can be seen in utero; in the neonate, it usually occurs in the first 48 hours of life.76 Unrecognized, this can result in an arrhythmia-induced cardiomyopathy Cardioversion is effective and the arrhythmia usually does not recur Most neonates do not require antiarrhythmic medications There is an association between atrial flutter in the fetus and the newborn and the subsequent development of AVRT.77 FIG 22.16 A 12-lead rhythm strip showing a narrow complex tachycardia in a 12-hour-old baby The sawtooth pattern of atrial flutter becomes even more manifest with transient atrioventricular nodal block Automatic Tachycardias Unlike reentrant tachycardias, automatic tachycardias are rapid discharges from an automatic focus distinct from the sinus node Typically these tachycardias have a “warm up and a cool-down” phase and respond to the autonomic tone of the individual Distinct from reentrant tachycardia, automatic tachycardias often cannot be initiated or terminated with programmed electrical stimulation and are less likely to terminate with cardioversion They do not use the AV node as part of the tachycardia circuit so do not routinely terminate with adenosine, although the use of this medication may allow for AV block and unmask an atrial tachycardia Atrial Ectopic Tachycardia AET is the most common arrhythmia associated with arrhythmia-induced cardiomyopathy in children.73 Although a P-wave morphology and axis usually differ from sinus rhythm, an AET focus near the sinus node or right upper pulmonary vein is hard to differentiate from sinus tachycardia, especially in patients with heart failure, where sinus tachycardia is expected Increased automaticity is the most likely mechanism; others include triggered activity and microreentry.78,79 AET usually occurs without structural heart disease but has been described after congenital heart disease surgery and in the setting of channelopathies.80 Arrhythmia-induced cardiomyopathy may occur in 1 in 4 children with AET; however, the presentation may vary from mild LV dysfunction to the need for heart failure medications; in rare cases it may require advanced mechanical heart failure therapies.82 Although β-blockers are often the first line of therapy in AET, drug failures are common and multiple antiarrhythmics may be utilized Catheter ablation is effective in AET In this procedure conscious sedation may be preferred to negate the potential that general anesthesia will suppress the tachyarrhythmia and reduce the likelihood of a successful ablation The use of electroanatomic mapping for ablation has improved success and decreased recurrence.83,84 Spontaneous resolution of AET can occur, especially in those presenting within the first year of life, where 74% had resolution.82 Although ablation has proven safe and effective, a trial of medical therapy in the youngest patients, in whom ablation may have more risk and where spontaneous resolution, is prudent Junctional Ectopic Tachycardia JET has two forms: occurring immediately after surgery (postoperative) or as a primary idiopathic arrhythmia (congenital) JET is due to abnormal automaticity in the region of the AV junction85 and is defined as a narrow QRS complex often with AV dissociation or retrograde atrial conduction in a 1 : 1 pattern.86 JET is most commonly seen in young children following complex congenital heart surgery (Fig 22.17) around the AV node with long cardiopulmonary bypass times and need for significant inotropic support.87 Postoperative JET is unique in that it is potentially life-threatening yet is self-limited Because of the clinical