The noninvasive findings that identify a pathway incapable of maintaining rapid conduction during AF include intermittent loss of conduction over the accessory pathway on the resting ECG or during ambulatory monitoring or abrupt loss of pre-excitation during exercise testing.294 297 The ECG should be evaluated closely to make certain the delta wave is truly absent, as accessory pathways (especially left lateral pathways) may demonstrate varying degrees of pre-excitation because of fusion between conduction over the accessory pathway and through the AV node, which may give the appearance of loss of pre-excitation if the subtle delta wave is not identified. Noninvasive tests have an approximately 90% positive predictive value and 30% negative predictive value for identifying pathways with life- If noninvasive evaluation suggests that the accessory pathway conducts poorly in the anterograde direction, although risk of life-threatening events is likely lower, the EP study still may be useful because of patient symptoms. I B-NR 2. An EP study is useful in symptomatic patients with pre-excitation to risk-stratify for life-threatening arrhythmic events.254,256,298 300 See Online Data Supplements 11 15. Most symptomatic patients with accessory pathways undergo catheter ablation, but in some instances, EP studies are performed to identify whether the patient is at increased risk of rapid conduction down the accessory pathway during AF and development of life-threatening ventricular arrhythmias. The most useful findings for risk stratification are an R-R interval <250 ms between 2 pre-excited complexes during induced AF; the presence of multiple accessory pathways; the finding of AVRT precipitating pre-excited AF; and an accessory pathway refractory period <240 ms.254,256,298 300 recommendations for anticoagulation mirror those for patients Similarly, the recommendations for anticoag- ulation with regard to either pharmacological or electrical car- dioversion of patients with atrial flutter are the same as those for patients with AF, as discussed in the 2014 AF guideline 7.2. Non Isthmus-Dependent Atrial Flutters Non isthmus-dependent atrial flutter or atypical flutter describes macroreentrant ATs that are not dependent on conduction through the CTI. A variety of circuits have been described, including a path around the mitral annulus (perimi- tral flutter), re-entry involving the left atrial roof, and re-entry around regions of scarring in the right or left atrium. Non isthmus-dependent atrial flutters often occur in patients with atrial scarring from prior heart surgery or ablation but also may occur in any form of heart disease or may be idiopathic.134,140,319 Non isthmus-dependent atrial flutters can coexist with CTI- dependent flutter or involve the presence of multiple atrial re- The reentrant circuits are classified as either macroreentrant AT (large; often several centimeters or longer in diameter) or microreentrant AT ( 2 cm in diameter), which may be indistinguishable from focal AT.321 In the presence of substantial atrial disease, prior surgery, or prior radiofrequency catheter ablation, the ECG flutter- wave morphology is not a reliable predictor of whether the flutter circuit involves the CTI. Although an ECG with a typical flutter appearance has good predictive value for CTI- dependent flutter in a patient who has not undergone prior catheter ablation of AF, the ECG appearance is less useful in predicting the flutter circuit in a patient who has previously undergone AF ablation.322 325 The presence of a positive or biphasic (but dominantly positive) deflection in V1, accom- panied by deflections in other leads inconsistent with typical counterclockwise atrial flutter, suggests the presence of an atypical flutter (Figure 17). Definitive diagnosis requires EP study and intracardiac mapping.326 Catheter ablation of non CTI-dependent flutter requires more extensive mapping than does ablation of CTI-dependent flutter, and success rates are lower (Table 8). The location of the circuit determines ablation approach and risks. The substrate for macroreentrant atrial arrhythmias after cardiac surgery is atrial scarring from atriotomy inci- sions and cannulation sites and from the underlying myo- pathic process of the valve disease itself; this is sometimes referred to as incisional atrial reentrant tachycardia. The location of the reentrant circuit depends on the type of surgi- cal approach, and common populations include patients who have undergone mitral valve surgery or have a repaired atrial These arrhythmias are also common after surgical or catheter ablation for AF.331,332 Both single- and dual-loop circuits, as well as focal ATs, can be present. It is useful to review the procedural notes to identify the location of atrial incisions or prior ablation that can assist with future mapping and ablation. The development of a microreentrant or macroreentrant left AT after AF ablation occurs in approximately 5% of This is less frequent if ablation is limited to pulmonary vein isolation. On the other hand, these arrhythmias Figure 13. Ongoing management of AVNRT. Colors correspond to Class of Recommendation in Table 1; drugs listed alphabetically. AVNRT indi- cates atrioventricular nodal reentrant tachycardia; pt, patient; and SHD, structural heart disease (including ischemic heart disease). Page et al 2015 ACC/AHA/HRS SVT Guideline e541 are more common in patients with longer-duration persistent AF or more dilated left atria or when linear ablation lesions Non reentrant focal arrhythmias often origi- nate at lesion edges or reconnected segments of prior isolated Reisolation of the pulmonary vein and ablation of any nonpulmonary vein foci are often effective in treating these arrhythmias. Detailed activation and entrain- ment mapping of the tachycardia during a second procedure result in effective ablation in approximately 90% of patients.335 Although right atrial CTI-dependent flutter may also occur, most of the tachycardias originate in the left atrium. As with all types of atrial flutter, it may be very difficult to achieve rate control in patients with post AF ablation non CTI-dependent flutter (far more so than in patients with preablation AF). When the ventricular response cannot be controlled with common rate-control medications, attempts at restoration of sinus rhythm with pharmacological therapy and cardioversion are often required. Many of the atrial flut- ters that are observed during the first 3 months after catheter ablation or after cardiac surgery will not recur later on. For this reason, it is advised that attempts at ablation of atrial flut- ter after AF ablation be deferred until after the 3-month wait- Rarely, pharmacological therapy and attempts at rhythm control with antiarrhythmic drug therapy fail to adequately control atrial flutter during the 3 months after AF ablation. In this situation, early repeat ablation is warranted. 7.3. Acute Treatment: Recommendations Recommendations for Acute Treatment of Atrial Flutter COR LOE Recommendations I A 1. Oral dofetilide or intravenous ibutilide is useful for acute pharmacological cardioversion in patients with atrial flutter.119,340 346 See Online Data and 17. Pharmacological cardioversion of atrial flutter is generally less effective than synchronized cardioversion and carries the potential risk of proarrhythmia but can be an option when sedation is not available or not well tolerated or when indicated by patient preference. Intravenous ibutilide converts atrial flutter to sinus rhythm in approximately 60% of cases.342 The major risk is torsades de pointes, which is more likely to occur in patients with reduced left ventricular ejection fraction. Patients receiving ibutilide should undergo continuous ECG monitoring during administration and for at least 4 hours after completion of dosing. Pretreatment with magnesium can increase the efficacy and reduce the risk of torsades de pointes.119 Anticoagulation issues for chemical cardioversion are the same as those for electrical cardioversion of atrial flutter.10 I B-R Intravenous or oral beta blockers, diltiazem, or verapamil are useful for acute rate control in patients with atrial flutter who are See Online Data and 17. It is often more difficult to achieve rate control for atrial flutter than for AF. Nonetheless, effective rate control may be achieved with beta blockers, diltiazem, or verapamil in patients with atrial flutter through a direct effect on the AV node. Hypotension is the main adverse effect. Intravenous diltiazem is the preferred intravenous calcium channel blocker for acute rate control because of its safety and Diltiazem and verapamil should be avoided in patients with advanced heart failure and in patients with heart block or sinus node dysfunction in the absence of pacemaker therapy. Verapamil and diltiazem also should not be used in patients with known pre- excitation. The heart rate control achieved with beta blockers is similar to that seen with verapamil and diltiazem. The rate-slowing effect of beta blockers is largely related to reduction of sympathetic tone. Esmolol is generally the preferred intravenous beta blocker because of its rapid onset.353 Care should be used in administering beta blockers for rate control in atrial flutter patients with decompensated heart failure or reactive airway disease.355 I B-NR Elective synchronized cardioversion is indicated in stable patients with well-tolerated atrial flutter when a rhythm-control strategy is being pursued.356 358 See Online Data and 17. Heart rates can be difficult to control in atrial flutter. Cardioversion for atrial flutter can be successful at lower energy levels than for AF.356 Anticoagulation issues for cardioversion are the same as those for patients with AF and are addressed in the 2014 AF guideline.10 Restoration of sinus rhythm is favored to avoid development of tachycardia-mediated cardiomyopathy, which is associated with a rapid ventricular response in atrial flutter. I B-NR Synchronized cardioversion is recommended for acute treatment of patients with atrial flutter who are hemodynamically unstable and do not respond to pharmacological therapies.75,208,356,359 See Online Data and 17. The ventricular rate in atrial flutter can be difficult to control with pharmacological therapy. In patients with any signs or symptoms of hemodynamic compromise attributed to atrial flutter, synchronized cardioversion (with appropriate considerations with regard to anticoagulation) should be pursued without delay. I C-LD Rapid atrial pacing is useful for acute conversion of atrial flutter in patients who have pacing wires in place as part of a permanent pacemaker or implantable cardioverter-defibrillator or for temporary atrial pacing after cardiac surgery.360 364 See Online Data and 17. Atrial pacing is effective at terminating flutter in >50% of cases.364 Atrial pacing is more commonly applied in situations in which atrial wires are already in place, such as in the postoperative setting or in patients with programmable cardiac implanted electrical devices. A temporary pacing wire may also be placed and atrial pacing for termination of atrial flutter can be useful when sedation is contraindicated, or in the setting of digitalis toxicity, in which DC cardioversion is contraindicated. Pace-termination is performed by pacing the atrium at a rate starting approximately 5% to 10% above the atrial flutter rate to achieve atrial entrainment and by maintaining pacing for 15 seconds, with repeated attempts at incrementally faster rates (reducing the pacing cycle length by 5 to 10 ms until normal sinus rhythm or AF occurs.364 When AF is precipitated, this is often more easily rate-controlled and may subsequently revert to sinus rhythm. Recommendations for anticoagulation with regard to pace-termination of atrial flutter are the same as those for chemical or electrical conversion of AF. 7.4. Ongoing Management: Recommendations I B-NR Acute antithrombotic therapy is recommended in patients with atrial flutter to align with recommended antithrombotic therapy for patients with AF.365 See Online Data and 17. The risk of stroke associated with AF is well established, and several RCTs have demonstrated the efficacy of anticoagulation for stroke prevention in patients with additional risk factors.366 Anticoagulation has also been shown to prevent stroke when administered during the weeks immediately before and after cardioversion.367 Whether atrial flutter carries a risk of stroke similar to that in patients with AF has been debated in the past but is now supported by limited evidence from mechanistic, observational, and prospective studies that include patients primarily with atrial flutter.365 369 Several reports have suggested that the risk of stroke in patients with atrial flutter is mitigated by anticoagulation. Meta-analysis of 13 studies of patients undergoing cardioversion of atrial flutter reported short-term stroke risks ranging from 0% to 7%, and the thromboembolism rate in patients with sustained flutter Other studies have reported similar risk and effectiveness of anticoagulation.369 Therefore, on the basis of the available data, recommendations for antithrombotic therapy for patients with atrial flutter are similar to those for patients with AF.10 IIa B-R Intravenous amiodarone can be useful for acute control of the ventricular rate (in the absence of pre-excitation) in patients with atrial flutter and systolic heart failure, when beta blockers are contraindicated or See Online Data and 17. Amiodarone may be useful for rate control in non pre-excited atrial flutter because of its slowing of conduction through the AV node and prolongation of AV nodal refractoriness. Because it has less negative inotropic effect than beta blockers, diltiazem, and verapamil and may produce less hypotension, it may be preferred in critically ill patients or in those with tenuous hemodynamic stability. Because of potential toxicity, amiodarone should not be used for long-term rate control in most patients. Although unlikely, amiodarone may result in conversion of atrial flutter to sinus rhythm, so potential risks and benefits should be considered for patients with atrial flutter lasting 48 hours who are not adequately anticoagulated.10 However, amiodarone is typically used for rate control only when other options are greatly limited. For patients with atrial flutter, antithrombotic therapy is recommended according to the same risk profile used for AF. Recommendations for Acute Treatment of Atrial Flutter (Continued) COR LOE Recommendations Recommendations for Ongoing Management of Atrial Flutter COR LOE Recommendations I B-R Catheter ablation of the CTI is useful in patients with atrial flutter that is either symptomatic or refractory to pharmacological See Online Data and 17. Rate control can be difficult to achieve in atrial flutter, and a rhythm control strategy is often chosen. Catheter ablation of CTI-dependent atrial flutter is often preferred to long-term pharmacological therapy; in this rhythm, the CTI represents the optimal target for ablation because a line of ablation between the tricuspid valve annulus and inferior vena cava can effectively interrupt the circuit. A variety of techniques are applicable, including various catheter types, energy delivery systems, and mapping and visualization tools; generally, success depends on creation of a complete line of block and permanent interruption of conduction across the CTI (Table 8). Successful ablation is often heralded by intraprocedural interruption of the arrhythmia and subsequent EP demonstration of bidirectional block across the ablated tissue. I C-LD Beta blockers, diltiazem, or verapamil are useful to control the ventricular rate in patients with hemodynamically tolerated See Online Data and 17. In some circumstances of persistent atrial flutter or in patients who have infrequent reasonably well-tolerated episodes of atrial flutter, a rate-control strategy may be chosen. In atrial flutter, the relatively slower atrial rate compared with AF often paradoxically results in more rapid AV nodal conduction because there is less concealed AV nodal conduction. Therefore, achieving adequate rate control can be difficult. Higher doses of beta blockers, diltiazem, or verapamil, and often a combination of agents, may be needed to achieve adequate rate control. Beta blockers are generally preferred in patients with heart failure. Avoidance of beta blockers, diltiazem, and verapamil in patients with pre-excited atrial flutter is recommended, given the potential for accelerated ventricular rates degenerating to ventricular fibrillation, as has been reported to occur rarely in similar patients with AF.274 I C-LD Catheter ablation is useful in patients with recurrent symptomatic non CTI-dependent flutter after failure of at least 1 See Online Data and 17. No prospective RCTs have compared the efficacy or safety of antiarrhythmic drugs with that of catheter ablation for non CTI-dependent atrial flutter. In general, catheter ablation of non CTI-dependent atrial flutter is substantially more difficult than ablation of CTI-dependent flutter because the anatomic circuits are complex, are often not anatomically defined, and can be difficult to locate. Knowledge of the prior surgical or ablation approach and detailed activation and entrainment mapping of the tachycardia are useful during attempts at ablation (Table 8). The location of the circuit determines ablation approach and risks. Observational data support the relative effectiveness and safety of catheter ablation in experienced centers.134,327 Many of the atrial flutters that are observed during the first 3 months after catheter ablation or cardiac surgery will not persist beyond the periprocedural period, so attempts at ablation can be deferred unless pharmacological therapy and/or cardioversion are unsuccessful.327 Page et al 2015 ACC/AHA/HRS SVT Guideline e543 I B-NR Ongoing management with antithrombotic therapy is recommended in patients with atrial flutter to align with recommended antithrombotic therapy for patients with AF.365 See Online Data and 17. The risk of stroke associated with AF is well established, and several RCTs have demonstrated the efficacy of anticoagulation for stroke prevention in patients with additional risk factors.366 Anticoagulation has also been shown to prevent stroke when administered during the weeks immediately before and after cardioversion.367 Whether atrial flutter carries a risk of stroke similar to that in patients with AF has been debated in the past but is now supported by limited evidence from mechanistic, observational, and prospective studies that include patients primarily with atrial flutter.365 369 Several reports have suggested that the risk of stroke in patients with atrial flutter is mitigated by anticoagulation. Meta-analysis of 13 studies of patients undergoing cardioversion of atrial flutter reported short-term stroke risks ranging from 0% to 7%, and the thromboembolism rate in patients with sustained flutter in 4 studies averaged 3% annually.365 Other studies have reported similar risk and effectiveness of anticoagulation.369 Therefore, on the basis of available data, recommendations for antithrombotic therapy for patients with atrial flutter are similar to those for patients with AF.10 IIa B-R The following drugs can be useful to maintain sinus rhythm in patients with symptomatic, recurrent atrial flutter, with the drug choice depending on underlying heart disease and comorbidities: See Online Data and 17. In patients in whom ablation is not being considered because of contraindications (such as underlying medical illness) or because of patient preference, a variety of antiarrhythmic drugs are available. These drugs act by suppressing triggers and altering atrial tissue refractoriness. Individual properties of each drug need to be considered for proper use. Much of the data pertaining to use of amiodarone in management of atrial arrhythmias has been derived from use in patients with AF.10 Few data are available for patients with atrial flutter. Amiodarone has significant toxicities, so it is used only when other treatments are contraindicated or ineffective. Nevertheless, administration is reasonable, particularly in patients with heart failure or significant underlying heart disease.376 Dofetilide may be more effective than many other drugs but must be started in an inpatient setting.346,377 The dose is adjusted on the basis of renal function, with close monitoring of the Q-T interval and subsequent monitoring for altered renal function. Sotalol, a class III antiarrhythmic, is generally well tolerated but is associated with typical beta blocker side effects, such as fatigue and The major potential cardiac toxicity for both drugs is torsades de pointes. IIa B-NR Catheter ablation is reasonable in patients with CTI-dependent atrial flutter that occurs as the result of flecainide, propafenone, or amiodarone used for treatment of AF.317,379 381 See Online Data and 17. Some patients with AF treated with propafenone, flecainide, or amiodarone will develop atrial flutter. In this circumstance, if flutter becomes the dominant arrhythmia, ablation of the CTI and continued use of the antiarrhythmic drug can decrease the incidence of atrial flutter and facilitate the pharmacological management of AF.379,380 IIa C-LD Catheter ablation of the CTI is reasonable in patients undergoing catheter ablation of AF who also have a history of documented clinical or induced CTI-dependent atrial flutter.381,382 See Online Data and 17. The indications for catheter ablation of AF are discussed in the 2014 AF guideline.10 When AF and atrial flutter coexist, 1 randomized study demonstrated that at 1-year follow-up, greater success in terms of arrhythmia suppression and quality-of-life score resulted from AF ablation (with or without atrial flutter ablation) than from atrial flutter ablation alone.381 It may be that AF ablation alone is sufficient to control both arrhythmias, although CTI ablation reduced the early postablation arrhythmia recurrence rate.382 IIa C-LD Catheter ablation is reasonable in patients with recurrent symptomatic non CTI-dependent flutter as primary therapy, before therapeutic trials of antiarrhythmic drugs, after carefully weighing potential risks and benefits of treatment See Online Data and 17. No prospective RCTs have compared the efficacy or safety of antiarrhythmic drugs with that of catheter ablation for non CTI-dependent atrial flutter. Observational data, however, support the relative effectiveness and safety of catheter ablation in experienced centers.135,327 Many of the atrial flutters that are observed during the first 3 months after ablation or cardiac surgery will not persist beyond the periprocedural period, so attempts at ablation can be deferred unless attempts at pharmacological therapy or cardioversion are IIb B-R Flecainide or propafenone may be considered to maintain sinus rhythm in patients without structural heart disease or ischemic heart disease who have symptomatic recurrent atrial flutter.383 385 See Online Data and 17. Data to support the recommendation for flecainide and propafenone for maintenance of sinus rhythm in patients with atrial flutter is derived from trials that pooled patients with AF and atrial flutter, with the vast majority of the patients having AF. It is therefore possible that these agents are not as effective for treating isolated atrial flutter as they are for AF.386 Flecainide and propafenone may result in slowing of the atrial flutter cycle length, which may lead to a rapid 1:1 ventricular response.387 Because of this, caution is advised with flecainide and propafenone in patients with atrial flutter at risk of 1:1 conduction. The risk may be reduced by coadministration of medications that slow AV nodal conduction, such as beta blockers, verapamil, or diltiazem. IIb C-LD 2. Catheter ablation may be reasonable for asymptomatic patients with recurrent atrial flutter.102,121,372 See Online Data and 17. Catheter ablation of atrial flutter is highly effective, with single-procedure success rates >90%102 and an excellent safety profile.102,121 In patients with recurrent atrial flutter, long-term maintenance of sinus rhythm is more likely with ablation than with pharmacological therapy.372 Also, ablation may avoid potential development of tachycardia-mediated cardiomyopathy. Recommendations for Ongoing Management of Atrial Flutter (Continued) COR LOE Recommendations 8. Junctional Tachycardia See Figure 20 for a representative ECG for junctional tachy- cardia and Figure 21 for the algorithm for ongoing manage- ment of junctional tachycardia. Junctional tachycardia is a rapid, occasionally irregular, narrow-complex tachycardia (with rates typically of 120 bpm to 220 bpm) (Figure 20). AV dissociation (often isorhythmic) may be seen, and when present, excludes the misdiagnosis of AVRT and makes AVNRT highly unlikely. Other SVTs are often misdiagnosed and misclassified as junctional tachycar- dia because of the frequent absence of demonstrable P waves in reentrant rhythms. Furthermore, when it is irregular, junc- tional tachycardia may be misdiagnosed as AF or MAT. The mechanism for junctional tachycardia is enhanced (abnormal) automaticity from an ectopic focus in the AV junction (includ- ing the His bundle).388 Junctional tachycardia is uncommon in adults388 ; it is typically seen in infants postoperatively, after cardiac surgery for congenital heart disease; this is also known as junctional ectopic tachycardia. As such, there is limited evidence with regard to diagnosis and management of junctional tachycardia in adult patients. Adults with junctional tachycardia typically have a relatively benign course, whereas infants and children with acquired or congenital junctional tachycardia have a high rate of death due to heart failure or an uncontrollable, inces- sant tachyarrhythmia. There are data to support the use of beta blockers, diltia- zem, flecainide, procainamide, propafenone, and verapamil for the treatment of junctional tachycardia (see recommenda- tions and references in Sections 8.1 and 8.2). The efficacy of amiodarone has been reported only in pediatric patients.389,390 Digoxin has not been well established as chronic therapy for junctional tachycardia. A related rhythm, nonparoxysmal junctional tachycar- dia (more commonly known as accelerated AV junctional rhythm), is far more common in adults than paroxysmal junctional tachycardia. The mechanism of nonparoxysmal junctional tachycardia is associated with automaticity or trig- gered activity. It occurs at a slower rate (70 bpm to 130 bpm) and is often due to digoxin toxicity391 or myocardial infarc- Treatment of this rhythm centers on addressing the underlying condition. In addition, there is some evidence that beta blockers,394 intravenous adenosine, or verapamil395 can terminate an accelerated junctional arrhythmia. A tran- sient junction rhythm may be seen after slow-pathway abla- tion for AVNRT.396 8.1. Acute Treatment: Recommendations Recommendations for Acute Treatment of Junctional Tachycardia COR LOE Recommendations IIa C-LD 1. Intravenous beta blockers are reasonable for acute treatment in patients with symptomatic junctional tachycardia.388 See Online Data Supplement 19. In a series studying junctional tachycardia in adult patients, beta-blocker therapy specifically intravenous propranolol was found to be modestly effective in terminating and/or reducing the incidence of tachycardia.388 IIa C-LD 2. Intravenous diltiazem, procainamide, or verapamil is reasonable for acute treatment in patients with junctional tachycardia.397 See Online Data Supplement 19. There may be a limited role for intravenous diltiazem, procainamide, or verapamil in patients in whom beta blockers are ineffective. The literature supports the use of intravenous verapamil, alone or in combination with procainamide; less is known about diltiazem The addition of procainamide to propranolol may be more effective than propranolol monotherapy.388 Figure 14. Acute treatment of orthodromic AVRT. Colors cor- respond to Class of Recommendation in Table 1; drugs listed alphabetically. *For rhythms that break or recur spontaneously, synchronized cardioversion is not appropriate. AVRT indicates atrioventricular reentrant tachycardia; ECG, electrocardiogram; and IV, intravenous. Page et al 2015 ACC/AHA/HRS SVT Guideline e545 8.2. Ongoing Management: Recommendations 9. Special Populations As discussed in the Scope (Section 1.4), the present docu- ment is aimed at the adult population ( 18 years of age) and offers no specific recommendations for pediatric patients. Nevertheless, a brief discussion of SVT in pediatric patients is included below, highlighting major considerations with regard to SVT in younger patients, including adolescent patients. SVT in young patients varies significantly from SVT in adult patients in terms of mechanism, risk of developing heart failure or cardiac arrest, risks associated with inter- ventional therapy, natural history, and psychosocial impact. Approximately half of pediatric SVT presents in the first 4 months of life, with age-related peaks in occurrence subse- quently at 5 to 8 years and after 13 years. Accessory pathway mediated tachycardia accounts for >70% of SVT in infants, decreasing to approximately 55% in adolescents.56,407 409 AVNRT increases with age, from 9% to 13% of SVT in infants, to 30% to 50% of SVT in teenagers. After 12 years of age, women are more likely to have AVNRT than men, and overall SVT is less frequent among African American and Hispanic patients than in the general pediatric population.56 Atrial flutter is seen in some neonates and in older children is predominantly observed after congenital heart disease. AF is uncommon in childhood, accounting for <3% of supraven- tricular arrhythmias, and may be a consequence of AVRT or AVNRT in adolescents or may be associated with repaired congenital heart disease. Symptoms of SVT vary with age: gastrointestinal or respiratory findings in infants, chest or abdominal pain in the younger child, and palpitations in the adolescent. Congestive heart failure is present in up to 20% of infants and in older children with incessant tachycardia and in rare cases may necessitate mechanical cardiopulmonary sup- port during initial therapy.410 Pre-excitation is present in 20% to 35% of children with SVT. The risk of ventricular fibrillation or SCD related to WPW in childhood is 1.3% to 1.6% and is highest in the first The risk of cardiac arrest is higher in patients with AVRT precipitating AF, short accessory con- nection refractory periods, and posteroseptal accessory path- Notably, the absence of prior symptoms does not preclude risk because cardiac arrest may be the initial mani- festation of pre-excitation.254,257,411 Risk stratification, such as with ambulatory 24-hour monitoring or treadmill exercise testing, is often considered for children with pre-excitation to assess persistence of pre-excitation.412 Pharmacological therapy of SVT in childhood is largely based on practice patterns because RCTs of antiarrhythmic medications in children are lacking. AV nodal blocking drugs are widely used for the most common arrhythmias, AVRT, and Recommendations for Ongoing Management of Junctional Tachycardia COR LOE Recommendations IIa C-LD 1. Oral beta blockers are reasonable for ongoing management in patients with junctional tachycardia.388 See Online Data Supplement 19. Beta blockers are often used as first-line chronic therapy for junctional tachycardia because of the important proarrhythmic effects and long- term toxicity of other agents that have been shown to be effective.389,398,399 When junctional tachycardia is paroxysmal, attention should be directed toward avoiding the potential for bradyarrhythmias and hypotension when beta-blocker therapy is initiated. IIa C-LD 2. Oral diltiazem or verapamil is reasonable for ongoing management in patients with junctional tachycardia.397 See Online Data Supplement 19. Junctional tachycardia caused by enhanced automaticity may be suppressed as effectively by diltiazem and verapamil as by beta blockers. In 1 study of an adult patient on a regimen of oral verapamil, procainamide, and digoxin in combination for prophylactic therapy, junctional tachycardia could not be induced by either atrial or ventricular overdrive pacing, programmed electrical stimulation, or isoproterenol.397 Less is known about oral diltiazem than verapamil, but it likely has a similar efficacy. IIb C-LD Flecainide or propafenone may be reasonable for ongoing management in patients without structural heart disease or ischemic heart disease who have junctional tachycardia.398,399 See Online Data Supplement 19. Studies supporting the use of flecainide for long-term control of junctional tachycardia were performed at a time when intravenous flecainide was given for acute control, followed by a transition to chronic oral therapy.398 Although the only data for propafenone stem from case series in infants and children, given that flecainide and propafenone reduce automaticity from the ectopic focus in the AV junction, either agent is reasonable, provided patients do not have structural heart disease or ischemic heart disease.213,400,401 IIb C-LD Catheter ablation may be reasonable in patients with junctional tachycardia when medical therapy is not effective or See Online Data Supplement 19. Radiofrequency ablation has been performed as a potentially curative therapy for junctional tachycardia since the early 1990s. However, in view of the reported 5% to 10% risk of AV block, catheter ablation is generally reserved for highly symptomatic patients in whom drug therapy has been ineffective or not tolerated (Table 8). Many practitioners use cryoablation as an alternative to radiofrequency ablation.132 Given that it is often difficult to distinguish junctional tachycardia from AVNRT on the ECG, EP study with the goal of ablation may be a helpful diagnostic and potentially therapeutic intervention. Junctional tachycardia may be observed during and after slow-pathway ablation of AVNRT, because of irritation of the compact AV node.406 This iatrogenic junctional tachycardia is transient and generally benign and can be distinguished from AVNRT through pacing maneuvers at EP study.396,405 It is crucial to recognize this phenomenon at the time of EP study because attempts to ablate the junctional tachycardia are unnecessary and could result in AV block. AVNRT. Higher initial doses of adenosine are needed in chil- dren than in adults, with children receiving from 150 mcg/kg Digoxin and propranolol have simi- lar efficacy in infants with SVT without pre-excitation.416 Digoxin is avoided in the presence of pre-excitation because its use in infancy has been associated with SCD or ventricu- Amiodarone, sotalol, propafenone, or flecainide can be used for refractory SVT in infants. In older children presenting with SVT, beta-blocker therapy is most often the initial therapy used. Because of the rare occurrence of adverse events with flecainide, including in patients without structural heart disease, ischemic heart disease, or ventricular dysfunction, flecainide is not used as a first-line medication in Figure 16. Abrupt loss of pre-excitation during exercise testing. 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. P-wave morphologies are shown for common types of atrial flutter; however, the P-wave morphology is not always a reliable guide to the re-entry circuit location or to the distinction between common atrial flutter and other macroreentrant ATs. *Exceptions to P-wave morphology and rate are common in scarred atria. bpm indicates beats per minute, and ECG, electrocardiogram. Reproduced with permission from January et al.10 SVT or tachycardia-induced cardiomyopathy or before sur- gery that may limit access for subsequent catheter-based pro- cedures. Recurrence rates for SVT after successful procedures are higher than reported in large adult series, ranging from 7% to 17%; whether this reflects technical differences, natural his- tory, or more long-term follow-up is unclear.427 429 Recurrence is highest among right-sided accessory pathways, particularly anteroseptal or multiple pathways, and in AT in the setting of complex congenital heart disease.427 429 Junctional ectopic tachycardia occurs predominantly in very young patients either as a congenital form or, more commonly, after intracardiac repair of congenital heart dis- ease. Nonpostoperative junctional tachycardia has been reported to respond to amiodarone or combination therapy including beta blockers, flecainide, procainamide, or propafe- Ablation for patients with refractory tachycardia or ventricular dysfunction has shown efficacy of 82% to 85%, but inadvertent AV block occurred in 18% and recurrence was seen in 14% of patients.130 Postoperative junctional tachy- cardia occurs in 2% to 10% of young patients undergoing intracardiac surgery, particularly for ventricular or AV septal defects, tetralogy of Fallot, transposition of the great arteries, and Norwood procedures.430,431 Treatment includes sedation with muscle relaxation, limitation of inotropic medications, reduction of core temperature to 34 to 35 C, atrial overdrive pacing, and procainamide or amiodarone infusions.416,432 435 In general, postoperative junctional tachycardia resolves and does not require ongoing therapy. Although this guideline focuses on adults, it should be noted that SVT may occur in the fetus and, if sustained, may put the fetus at risk of cardiovascular collapse mani- fested by hydrops. Mothers require safety monitoring by adult cardiologists during treatment. The most common mechanisms for fetal SVT are AVRT and atrial flutter.436 Persistent SVT with hydrops carries a high mortality rate, and therefore, prompt and aggressive treatment is war- ranted. Maternal administration of antiarrhythmic agents has been shown to be effective through transplacental delivery. Flecainide, sotalol, and digoxin, alone or in com- bination, have demonstrated arrhythmia termination rates of 60% to 90%, depending on whether hydrops is pres- In cases refractory to the aforementioned drugs, maternal oral loading for 2 to 7 days with amiodarone may Treatment of fetal SVT has provided safety data for treatment of arrhythmias in women during pregnancy, as addressed in Section 9.3. Figure 18. Acute treatment of atrial flutter. Colors correspond to Class of Recommendation in Table 1; drugs listed alphabetically. *Anticoagulation as per guideline is mandatory. For rhythms that break or recur spontaneously, synchronized cardioversion or rapid atrial pacing is not appropriate. IV indicates intravenous. Figure 19. Ongoing management of atrial flutter. Colors cor- respond to Class of Recommendation in Table 1; drugs listed alphabetically. *After assuring adequate anticoagulation or excluding left atrial thrombus by transesophageal echocardiog- raphy before conversion. Should be combined with AV nodal blocking agents to reduce risk of 1:1 conduction during atrial flutter. AV indicates atrioventricular; SHD, structural heart disease (including ischemic heart disease). Page et al 2015 ACC/AHA/HRS SVT Guideline e549 9.2. Patients With Adult Congenital Heart Disease See Figure 22 for the algorithm for acute treatment of non pre-excited SVT in adult congenital heart disease (ACHD) patients; and Figure 23 for the algorithm for ongoing manage- ment of non pre-excited SVT in ACHD patients. 9.2.1. 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. The upper panel shows sinus rhythm. The lower panel shows tachycardia onset with the characteristic finding of dissociation of the QRS and P waves (narrow arrows on P waves). The large arrow signi- fies continuous recording. Reproduced with permission from Blomstr m-Lundqvist et al.11 Figure 21. Ongoing management of junctional tachycardia. Colors correspond to Class of Recommendation in Table 1; drugs listed alphabetically. SHD indicates structural heart disease (including ischemic heart disease). cyanotic heart disease, single or systemic right ventricles, or Ebstein anomaly, is essential to decision making during SVT treatment. In certain conditions, the presence of cyanosis or severe ventricular dysfunction requires consideration of high- risk cardioversion with resuscitation measures at hand; usu- ally, this decision is made at centers with specialized expertise. Management of ACHD patients should be undertaken only in collaboration with a cardiologist who has specialized training or experience in managing such patients. RCTs assessing antiarrhythmic medication efficacy are lacking. Beta-blocking medications offer the advantages of outpatient medication initiation and may provide protection from tachycardia-mediated hypotension or ischemia. Risks of proarrhythmia are increased with the use of sotalol, ibutilide, dofetilide, and particularly flecainide and require in-hospital and is reserved for patients without ventricular dysfunction who do not respond to other therapy. Sinus node dysfunction may contribute to the development of atrial arrhythmias and may become exacerbated with antiarrhythmic medications. Atrial antibradycardia pacing to maintain a consistent physi- ological heart rate may decrease the frequency of tachycardia episodes and may improve functional capacity.364,370,371 Atrial antitachycardia pacing to terminate atrial reentry tachycardia is an effective approach when feasible.364,370,371 Overall acute success rates of catheter ablation procedures for SVT in ACHD patients range from 70% to 85%, with recurrences in 20% to 60% of patients within 2 years.452 457 Catheter ablation is challenged by limitations of venous access to the heart, hypertrophied atrial tissue, multiple atrial reen- trant circuits, and atrial baffles partitioning the coronary sinus and CTI to the pulmonary venous atrium. Because the CTI is involved in >60% of atrial reentry circuits, an initial strat- egy targeting this region is often used. Highest success rates are achieved in patients with atrial septal defects, approach- ing 90% to 100%, although subsequent AF has been reported Because of the need for sophisticated knowledge of anatomy, advanced mapping capability, cardiac anesthesia with careful peripro- cedural monitoring, and repeat ablations, such patients should be referred to centers with extensive experience in complex congenital heart disease ablations. The development of atrial arrhythmias in ACHD patients is often an indicator of progressive hemodynamic changes, which require in-depth functional and hemodynamic assess- ment. Intervention for residual hemodynamic/structural defects may need to be planned as part of chronic arrhyth- mia management. Patients with Ebstein anomaly or repaired tetralogy of Fallot may have significant pulmonary regurgita- tion, tricuspid regurgitation, or both, which might benefit from reoperation. In some settings, integration of operative ablation techniques with hemodynamic repair may be optimal. 9.2.2. Acute Treatment: Recommendations Recommendations for Acute Treatment of SVT in ACHD Patients COR LOE Recommendations I C-LD Acute antithrombotic therapy is recommended in ACHD patients who have AT or atrial flutter to align with recommended antithrombotic therapy for patients with AF.365 See Online Data and 17. The risk of stroke associated with AF is well established, and several RCTs have demonstrated the efficacy of anticoagulation for stroke prevention in patients with additional risk factors.366 Anticoagulation has also been shown to prevent stroke when administered during the weeks immediately before and after cardioversion.31,367 Whether atrial flutter carries a risk of stroke similar to that in patients with AF has been debated in the past but is now supported by limited evidence from mechanistic, observational, and prospective studies that include patients primarily with atrial flutter.365 369 Several reports have suggested that the risk of stroke in patients with atrial flutter is mitigated by anticoagulation. Meta-analysis of 13 studies of patients undergoing cardioversion of atrial flutter reported short-term stroke risks ranging from 0% to 7%, and the thromboembolism rate in patients with sustained flutter in 4 studies averaged 3% annually.365 Other studies have reported similar risk and effectiveness of anticoagulation.369 ACHD patients with nonfibrillatory atrial tachyarrhythmias appear to be at high risk, as well.367,459 Therefore, on the basis of available data, recommendations for antithrombotic therapy for ACHD patients who also have AT or atrial flutter are similar to those for patients with AF.10 I B-NR 2. Synchronized cardioversion is recommended for acute treatment in ACHD patients and SVT who are hemodynamically unstable.75,460 See Online Data Supplement 20. A small observational study demonstrated safety and efficacy of synchronized cardioversion in ACHD patients, with sinus rhythm achieved in 94% of Guideline-directed medical therapy supports this treatment approach, stressing that electrical cardioversion is the safest and most effective way of treating SVT associated with hemodynamic instability and should be considered early in the management of such patients.75 Modification of electrode pad placement may be necessary, by using an anterior-posterior configuration in patients with marked atrial enlargement or positioning strategically according to the individual arrhythmia and anatomic substrate, including consideration of the possibility of dextrocardia. I C-LD Intravenous diltiazem or esmolol (with extra caution used for either agent, observing for the development of hypotension) is recommended for acute treatment in ACHD patients and SVT who are hemodynamically stable.461,462 See Online Data Supplement 21. Very limited data exist on the use of calcium channel blocking or beta-blocking medications for rate control or termination of AT or atrial flutter specifically associated with ACHD. Rate control of AT or atrial flutter with rapid AV conduction may be useful to improve hemodynamic status while planning conversion strategies. Patients with congenital heart disease, particularly single-ventricle physiology or systemic right ventricles, may not tolerate ventricular rates >120 bpm for many hours.29 Either drug may be associated with the development of hypotension in up to 20% of patients.462 Because of the high incidence of ventricular dysfunction in this population, particular attention should be given to monitoring the patient for development of hypotension, which would necessitate prompt dose adjustments or change of treatment strategy. I B-NR 4. Intravenous adenosine is recommended for acute treatment in ACHD patients and SVT.207,463 465 See Online Data Supplement 20. Observational studies support the use of adenosine to terminate AVNRT, SVT using an accessory pathway, and some forms of focal AT. These mechanisms account for <25% of SVT in adults with repaired congenital disease.207,463 Intravenous adenosine is unlikely to terminate atrial reentry tachycardia or atrial flutter, which represents >70% of SVT episodes in this population, but it may be diagnostic by producing transient AV block, which would make the atrial activity visible.464,465 Page et al 2015 ACC/AHA/HRS SVT Guideline e551 9.2.3. Ongoing Management: Recommendations Recommendations for Ongoing Management of SVT in ACHD Patients COR LOE Recommendations I C-LD Ongoing management with antithrombotic therapy is recommended in ACHD patients and AT or atrial flutter to align with recommended antithrombotic therapy for patients with AF.365 See Online Data and 17. The risk of stroke associated with AF is well established, and several RCTs have demonstrated the efficacy of anticoagulation for stroke prevention in patients with additional risk factors.366 Anticoagulation has also been shown to prevent stroke when administered during the weeks immediately before and after cardioversion.31,367 Whether atrial flutter carries a risk of stroke similar to that in patients with AF has been debated in the past but is now supported by limited evidence from mechanistic, observational, and prospective studies that include patients primarily with atrial flutter.365 369 Several reports have suggested that the risk of stroke in patients with atrial flutter is mitigated by anticoagulation. Meta-analysis of 13 studies of patients undergoing cardioversion of atrial flutter reported short-term stroke risks ranging from 0% to 7%, and the thromboembolism rate in patients with sustained flutter in 4 studies averaged 3% annually.365 Other studies have reported similar risk and effectiveness of anticoagulation.369 ACHD patients with nonfibrillatory atrial tachyarrhythmias appear to be at high risk, as well.367,459 Therefore, on the basis of available data, recommendations for antithrombotic therapy for ACHD patients who also have AT or atrial flutter are similar to those for patients with AF.10 I C-LD Assessment of associated hemodynamic abnormalities for potential repair of structural defects is recommended in ACHD patients as part of therapy for SVT.25,29 See Online Data Supplement 20. The development of AT, atrial flutter, or AF in ACHD patients is often associated with progressive hemodynamic deterioration of the underlying disease. Surgical treatment of the hemodynamic problems does not eliminate atrial arrhythmias, and ablation of atrial arrhythmias alone could allow significant hemodynamic issues to progress and potentially deteriorate. Successful treatment involves assessing both the arrhythmia and the contributing hemodynamic changes and addressing both when indicated and feasible. Early experience in adults with unoperated atrial septal defects and atrial arrhythmias demonstrated the importance of an integrated approach for arrhythmia and hemodynamic problems; similar principles apply to patients with tetralogy of Fallot, Ebstein anomaly, and single-ventricle physiology; these patients are at highest risk of arrhythmia development, with concurrent hemodynamic abnormalities. For example, patients with ASD who underwent surgery before the age of 25 years had better long-term outcomes and a lower incidence of atrial arrhythmias than those who underwent surgery later in life.475 Closure of significant atrial septal defects in adults even later in life improves morbidity and survival476 but is associated with new (7%) or recurrent (60%) AT.475 Arrhythmias still can be treated successfully when they develop later after surgical corrections; catheter ablation of atrial arrhythmias associated with ASD repair is highly successful, with acute success rates reported as 93% to 100%.449,458,477 Therefore, patients with unoperated significant ASD and arrhythmias should undergo ablation of the AT, as well as closure of the ASD. The choice of catheter versus surgical approaches to therapy is determined by anatomic features of the ASD likely to be successfully addressed with a catheter approach. No randomized comparison trials of catheter versus surgical closure of ASD combined with arrhythmia intervention have been reported. Surgical closure of large ASDs combined with arrhythmia surgery for AT or fibrillation can be safely performed, with 6.5% occurrence of AF reported during 2 years of follow-up.478 IIa B-NR Intravenous ibutilide or procainamide can be effective for acute treatment in ACHD patients and atrial flutter who are See Online Data Supplement 20. A small observational study reported that intravenous ibutilide was successful in conversion of 71% of acute episodes of atrial flutter in ACHD patients; torsades de pointes or nonsustained VT was reported in 2.7% of episodes.468 Pretreatment with magnesium may reduce the incidence of postibutilide ventricular arrhythmias. Small studies support the use of intravenous procainamide as adjunctive therapy for acute therapy of atrial flutter because it improves efficacy of pacing conversion of atrial flutter.466,467 IIa B-NR Atrial pacing can be effective for acute treatment in ACHD patients and SVT who are hemodynamically stable and anticoagulated as per current guidelines for antithrombotic therapy in patients with AF.466,469 472 See Online Data Supplement 20. Small observational studies support the efficacy of atrial pacing to successfully terminate 54% to 82% of acute episodes of AT or atrial Atrial pacing is an effective alternative, particularly when concerns about the use of antiarrhythmic medications or significant sinus node dysfunction exist. IIa B-NR Elective synchronized cardioversion can be useful for acute termination of AT or atrial flutter in ACHD patients when acute pharmacological therapy is ineffective or contraindicated.460 See Online Data Supplement 20. ACHD patients are at increased risk of congestive heart failure and/or atrial thrombus formation with prolonged episodes of AT or atrial flutter. Pharmacological conversion in patients with complex anatomy, ventricular dysfunction, or prolonged QTc intervals may result in significant proarrhythmia or acute hemodynamic deterioration. Early assessment for cardiac thrombus with transesophageal echocardiogram followed by synchronized cardioversion may be preferable to prolonged or multiple attempts to achieve pharmacological cardioversion. Because of frequent coexistent sinus node dysfunction and ventricular dysfunction, the need for chronotropic or inotropic intervention should be anticipated, with appropriate personnel and support present. Modification of electrode pad placement may be necessary, by using an anterior-posterior configuration in patients with marked atrial enlargement or positioning strategically according to the individual arrhythmia and anatomic substrate, including consideration of the possibility of dextrocardia. IIb B-NR Oral dofetilide or sotalol may be reasonable for acute treatment in ACHD patients and AT and/or atrial flutter who are See Online Data Supplement 20. Small observational studies support the use of oral dofetilide474 to acutely convert AT to sinus rhythm in 70% to 85% of episodes of acute AT or atrial flutter. Proarrhythmic events are more commonly reported with dofetilide. One small study of 20 patients reported that 10% experienced torsades de pointes after dofetilide474 ; both proarrhythmic events occurred in patients with single-ventricle physiology. The risk of proarrhythmia or worsening ventricular function requires arrhythmia monitoring with use. Recommendations for Acute Treatment of SVT in ACHD Patients (Continued) COR LOE Recommendations IIa B-NR Preoperative catheter ablation or intraoperative surgical ablation of accessory pathways or AT is reasonable in patients with SVT who are undergoing surgical repair of Ebstein anomaly.479 485 See Online Data Supplement 20. The prevalence of SVT among patients with Ebstein anomaly was 33% in 1 large series, the highest noted among ACHD and increased with age. AT, atrial flutter, or AF develops in 50% of patients with Ebstein anomaly and significant tricuspid regurgitation. Right-sided accessory pathways are present in 15% to 30% of patients with Ebstein anomaly and may be multiple in up to 29% of those patients. Catheter ablation of accessory pathways in patients with Ebstein anomaly is associated with lower success rates than for other populations, acute success rate of 75% to 89% of procedures, with acute recurrence in 25% In a series of 83 adults undergoing arrhythmia surgery at the time of surgical repair of Ebstein anomaly, accessory pathways were present in 32%, and atrial flutter/fibrillation was noted in 54%,483 with no recurrence of AP after surgery. Successful surgical ablation of accessory pathways has been reported in 92% to 100%.483,484 In a series of patients undergoing right atrial maze procedures or isthmus ablation for atrial flutter/fibrillation in association with repair of Ebstein anomaly, freedom from recurrent flutter/fibrillation was 75% during 34 months of follow-up.483 In a comparison study of combined operative arrhythmia surgery with repair, versus catheter ablation followed by surgical repair, the combined approach was effective in 94% of cases versus 76% of patients treated with the catheter approach alone.484 In a series of patients undergoing repair of Ebstein anomaly, patients who underwent preoperative EP study with intraoperative ablation of arrhythmia substrate had lower risk of SCD than patients without In patients with Ebstein anomaly undergoing planned surgical intervention, an integrated approach of arrhythmia intervention has been demonstrated to be safe and effective. IIa B-NR 2. Oral beta blockers or sotalol therapy can be useful for prevention of recurrent AT or atrial flutter in ACHD patients.218,447,486 See Online Data Supplement 20. Beta blockers may decrease catecholamine-related triggers and provide AV nodal blockade during recurrent atrial arrhythmias. One study of adults with transposition of the great arteries and prior atrial switch repairs with implanted defibrillators demonstrated SVT preceding VT in 50% of patients; use of beta-blocker medications in this population was associated with decreased incidence of appropriate defibrillator shocks.486 Observational studies on the use of sotalol in ACHD patients report freedom from recurrent AT in 41% to 46% of patients during short-term follow-up.218,487,488 Use of either medication in the setting of significant sinus node dysfunction may exacerbate bradycardia and requires careful monitoring. Initiation of sotalol in this population is recommended during inpatient monitoring for proarrhythmia for 48 to 72 hours. IIa B-NR 3. Catheter ablation is reasonable for treatment of recurrent symptomatic SVT in ACHD patients.330,449,452,454,457,458,489 492 See Online Data Supplement 20. Multiple observational and multicenter studies have demon strated acute success rates between 65% and 100% for treatment of SVT associated with ACHD.452,454,455,457,489,493,494 Acute success rates vary by tachycardia mechanism and type of congenital heart disease and repair. Success rates are highest for SVT associated with AVNRT (>80%),490,494 accessory pathways (75% to 89% among patients with Ebstein or focal AT (80% to 100%).492,494,495 Success rates for catheter ablation of AT or atrial flutter are significantly lower than that reported in patients without ACHD, with overall 65% to 82% acute success in mixed anatomic substrates,452,454,455,457,493,494 but success rates have improved with advanced mapping and ablation techniques.494 Acute success rates in ablation of AT or atrial flutter varies significantly by type of congenital heart disease, ranging from 93% to 100% in patients with repaired ASD,330,449,458 85% to 100% in atrial baffle repairs of transposition of the great arteries,490,492 and 54% to 75% of univentricular heart or Fontan repairs.457,490,495 Older age and presence of univentricular heart physiology was associated with decreased acute success rates in a series of 193 ablations of AT.457 Recurrent AT has been reported in 20% to 85% of patients during short-term follow-up, with development of AF reported in 7% to 30% of patients.330,449,454,493 Recurrent SVT may represent the same or a new reentrant circuit, and arrhythmia burden may be decreased by ablation procedures. Ablation procedures in patients with complex congenital heart disease are best performed in centers with advanced mapping techniques and expertise in congenital heart disease.25,29,496 IIa B-NR 4. Surgical ablation of AT or atrial flutter can be effective in ACHD patients undergoing planned surgical repair.497 508 See Online Data Supplement 20. In patients with symptomatic SVT undergoing planned surgical repairs of structural heart disease or ischemic heart disease, observation studies report that arrhythmia surgery can be integrated into the operation with high efficacy and without increased surgical morbidity.497 500 In populations including those with tetralogy of Fallot/double-outlet right ventricle, tricuspid valve repairs, and ASD, rates of freedom from recurrent AT or atrial flutter have been reported as 73% to 93% without antiarrhythmic medications during medium-term follow-up of 2.5 to 10 years. Catheter ablation may be attempted in specialized centersbefore surgical Fontan repair. There are no RCTs comparing efficacy of catheter versus surgical ablation of AT or atrial flutter in patients with prior Fontan repairs. The incidence of AT or atrial flutter in patients with prior Fontan repairs approaches 60% and increases with advancing age. Catheter ablation success rates in this subset of patients are lower than for other lesions,457 with acute success in 54% to 75%, and with recurrent AT in 27% to 50% of patients within 2 to 4 years490,495 ; death or transplantation was reported in 27% during follow-up. Several observational studies of surgical resection and ablation for AT or atrial flutter associated with Fontan conversion reported rates of freedom from AT of 12% to 16% during follow-up extending to 8 years501 505 ; death or transplantation was reported in 6% to 14% during follow-up. Performance of a modified right atrial maze procedure versus CTI ablation was associated with lower recurrence rates.501 Alternatively, surgical repairs without arrhythmia intervention are associated with high recurrence rates of AT. Arrhythmia surgery can be combined with hemodynamic surgical revision with low mortality rate and improved medium-term freedom from arrhythmia recurrence and deathin this population. IIb B-NR Atrial pacing may be reasonable to decrease recurrences of AT or atrial flutter in ACHD patients and sinus node See Online Data Supplement 20. Small observational studies support the use of atrial pacing in patients with recurrent AT or atrial flutter to reduce the frequency of tachycardia episodes. The pacing rate is programmed to maintain atrial pacing for the majority of the time in patients with sinus node dysfunction, significantly reducing tachycardia recurrences to 11% in 1 study.509,510 In addition, the implanted pacemaker can be used for termination of recurrent episodes of AT or atrial flutter.472 Recommendations for Ongoing Management of SVT in ACHD Patients (Continued) COR LOE Recommendations Page et al 2015 ACC/AHA/HRS SVT Guideline e553 Pregnancy may confer an increased susceptibility to a variety of arrhythmias, even in the absence of underlying heart Pregnancy is also associated with an increased risk of arrhythmia exacerbation, such as more frequent and refractory tachycardia episodes, in patients with a pre-existing An important consideration is that adverse maternal and fetal outcomes have been reported as a result of SVT in pregnancy.515 Although there is potential tox- icity to the fetus with certain pharmacological and nonphar- macological therapies, safe options exist to allow for treating most cases of maternal SVT effectively. The literature on therapeutic options for the management of arrhythmias in pregnancy is generally limited to single case reports or small series and favors the use of older antiarrhyth- mic agents because of more abundant reports on the safe use of these drugs. Experience with use of drugs in pregnancy also comes from treating a variety of maternal and fetal condi- tions, not maternal SVT alone. Although all medications have potential side effects to both the mother and the fetus at any stage of pregnancy, if possible, drugs should be avoided in the first trimester, when risk of congenital malformations is great- est. The lowest recommended dose should be used initially, accompanied by regular monitoring of clinical response. 9.3.1. Acute Treatment: Recommendations IIb B-NR 2. Oral dofetilide may be reasonable for prevention of recurrent AT or atrial flutter in ACHD patients.447,474,487,488 See Online Data Supplement 20. Two small observational studies on the use of oral dofetilide for ACHD patients report a high rate of acute conversion of AT or atrial flutter, with longer-term efficacy of the drug (defined by either complete suppression or partial improvement of symptoms) ranging from 70% to 85%. 