FIG 22.14 Rhythm strip from a 4-month-old with a narrow complex supraventricular tachycardia (SVT) breaking through on flecainide and propranolol The rate of the SVT is 190 beats/min The tachycardia broke as an intravenous line was being placed The arrow shows the first sinus beat The abrupt termination of the SVT is consistent with a reentrant type of arrhythmia Natural History of Neonatal/Infant Supraventricular Tachycardia Although episodes of SVT are common during infancy, most patients are free of tachycardia during early childhood, although some infants do not have a recurrence of SVT after the initial presentation.65 Natural history studies have suggested that approximately 30% of infants lose SVT inducibility by 1 year of age.66 Factors at presentation, characteristics of the tachycardia, or data from an initial esophageal EPS failed to predict which infants would have continued SVT recurrences and thus require antiarrhythmic medication and which infants would not need medication.62 However, all infants with the diagnosis of AVNRT continued to have inducible SVT at 1 year of age Most infants are free of medications at 1 year of age Medical Management of Supraventricular Tachycardia The use of chronic antiarrhythmic medications in the infant may prevent recurrent SVT events and allow the time needed for SVT resolution There have been few clinical trials to direct chronic SVT management in children, and the choice of antiarrhythmic medications is often based on personal preference and institutional practice as opposed to data from controlled clinical trials In the first randomized controlled trial of medical prophylaxis for SVT in a pediatric population, the researchers detected no differences in SVT recurrence between digoxin and propranolol, the two most common clinical choices for SVT prophylaxis in infants.67 A low SVT recurrence rate was seen in both groups In this study, all recurrences were seen in the first few weeks of life, and the majority of patients were arrhythmia free at 4 months of age Currently it is standard practice to use prophylactic medication for 6 to 12 months, but this duration of therapy may not be necessary Both digoxin and propranolol represent a reasonable first-line choice for the neonate with SVT However, if WPW syndrome is present, digoxin is not recommended owing to reports that this can shorten the effective refractory period of the accessory connection.68 In an older child a β-blocker with twice daily dosing may be preferable and atenolol is a reasonable first-line agent Decisions concerning the need for other antiarrhythmic agents depend on the tachycardia burden and symptoms, coexisting structural and functional heart disease, personal experience, and institutional practice Numerous agents exist, although few have had rigorous testing in a pediatric population Catheter Ablation of Supraventricular Tachycardia Decisions are often based on input from the patient and family Pediatric catheter ablation indications were assessed in two large pediatric studies, and the most common indication for catheter ablation was patient and parent wishes.69,70 Children with WPW syndrome are different Because this condition is associated with a small risk of sudden death, there should be a low threshold for ablation in this population, with patient age and size factored into the decision Animal studies suggest lesion growth when ablations are undertaken in immature animals, and risks have been shown to be increased in children weighing less than 15 kg.71,72 Postponing an ablation allows time for substrate resolution as well as the patient's somatic growth, which can decrease the risk of the procedure Ablation is not without risk, but the risk is small Thus the small and immediate risk of the ablation must be weighed against the lifetime symptom burden, ease of SVT management, and—in children with WPW syndrome—the lifetime risk of sudden death Permanent Form of Junctional Reciprocating Tachycardia PJRT is an accessory pathway–mediated tachycardia with a long RP interval; it occurs predominantly in infants and children (Fig 22.15) The pathway can be located anywhere in the AV junction but is usually located in the posteroseptal region This is a tachycardia with a long VA interval, called a long RP′ tachycardia The typical ECG of PJRT is that of negative P waves in leads II, III, aVF, given the typical inferior location of this unique accessory pathway Because the AV node constitutes the anterograde limb of this tachycardia, it will likely terminate with adenosine; most often, however, it quickly recurs Pathways are tortuous and slow conducting; thus the tachycardia is often incessant, and PJRT is the second most common cause of arrhythmia-induced cardiomyopathy in children.73 In a large review of children with PJRT, 27% presented in fetal life, 7% of these with hydrops, which is a fetal manifestation of arrhythmia-induced cardiomyopathy.74 Isolation of the AV junction is a continuing process that may not be complete at birth, and the presence of accessory connections crossing the annulus fibrosus could result in persistent perinatal SVT Although most children with PJRT present with palpitations or are noted to have rapid heart rates, in this series of 194 children, 18% presented with cardiomyopathy.74 Cardiomyopathy was more likely to occur in children with longer RP interval/cycle length ratios, consistent with an accessory pathway with slow retrograde conduction and a wide, excitable gap PJRT is often incessant, and those with incessant PJRT had longer RP intervals, were younger at diagnosis, and more often had cardiomyopathy The clinical course of PJRT is not benign and spontaneous resolution is unlikely  ... although few have had rigorous testing in a pediatric population Catheter Ablation of Supraventricular Tachycardia Decisions are often based on input from the patient and family Pediatric catheter ablation indications were assessed in two large pediatric studies, and the most... Decisions are often based on input from the patient and family Pediatric catheter ablation indications were assessed in two large pediatric studies, and the most common indication for catheter ablation was patient and parent wishes.69,70