Clinical Features SVT is observed in 10% to 20% of ACHD patients, and is asso- ciated with a significantly increased risk of heart failure, stroke, The most common mechanism of SVT inACHD patientsismacroreentrantAT(alsocalledflutter),whichaccounts for at least 75% of SVT and frequently involves the CTI. Focal AT, AVNRT, and accessory pathway mediated tachycardia each account for less than about 8% of SVT, whereas the incidence of AF is about 10% and increases with age.133,445 449 AT occurs in 20% to 45% of adults with Ebstein anomaly, single-ventricle/ Fontan procedures, tetralogy of Fallot, transposition of the great arteries, and atrial septal defects.449 451 The management of SVT in ACHD patients is influenced by the underlying cardiac anatomy and surgical repair, the cur- rent hemodynamic sequelae of the anatomy and repairs, and mechanism of SVT. The ventricular rate during SVT may be slowed because of variable AV conduction, which can result in a delay in recognizing tachycardia and the development of congestive failure. Recognition of severe forms of congeni- tal heart disease, including unrepaired or palliated defects, Table 8. Success and Complication Rates for Ablation of SVT* Arrhythmia Acute Success Recurrence Rate Major Complications References Common SVTs Overall 3%102 PPM 0.7%102 Death 0%102 AVRT/accessory pathway 93%102,103 Overall 2.8%102 PPM 0.3%102 Death 0.1%102 CTI-dependent atrial flutter 97%102 Overall 0.5%102 PPM 0.2%102 Pericardial effusion 0.3%102 Less common SVTs complications N/A) *Data in this table are derived from multiple observational studies and registries, and as such may not always reflect current practice. AT indicates atrial tachycardia; AVNRT, atrioventricular nodal reentrant tachycardia; AVRT, atrioventricular reentrant tachycardia; CHB, complete heart block; CTI, cavotricuspid isthmus; JT, junctional tachycardia; N/A, not available; PPM, permanent pacemaker; and SVT, supraventricular tachycardia. Figure 20. Surface electrocardiographic recording from leads VI, II, and V5 in a patient with junctional tachycardia. 