During exercise treadmill testing, this patient abruptly lost pre-excitation at a heart rate of 117 bpm. Beginning abruptly with the beat under the arrow, the PR interval normalizes, and the QRS changes from pre- excited to narrow. Figure 15. Ongoing management of orthodromic AVRT. Colors correspond to Class of Recommendation in Table 1; drugs listed alpha- betically. AVRT indicates atrioventricular reentrant tachycardia; ECG, electrocardiogram; pt, patient; and SHD, structural heart disease (including ischemic heart disease). Page et al 2015 ACC/AHA/HRS SVT Guideline e547 Catheter ablation can be successfully performed in chil- dren of all ages, with acute success rates comparable to those reported in adults.281,282,420,421 Success rates are influenced by the presence of structural heart disease or ischemic heart dis- ease and are highest in left-sided accessory pathways and lowest for AT. Complications were reported in 4% to 8% of the initial large series, with major complications in 0.9% to 3.2%, and complication rates were higher in patients weighing The implications of complications, including AV block requiring pacing, perforation, and coronary artery or mitral valve injury, are profound in young patients.423 425 In early series, death was reported in 0.12% of children with normal hearts and was associated with lower weight and increased number of ablation lesions.426 Increased institu- tional experience, advanced mapping techniques, and use of cryoablation have reduced the incidence of complications, as well as the radiation exposure associated with the procedure. Although most centers perform elective ablation for children weighing >12 kg to 15 kg, ablation in younger or smaller chil- dren is generally reserved for those with medically refractory Figure 17. Classification of atrial flutter/atrial tachycardias. Diagram summarizing types of ATs often encountered in patients with a his- tory of atrial fibrillation, including those seen after catheter or surgical ablation procedures. 