Clinical Questions

• 1.
  

  Timing and indications for RFCA in patients with congenital heart disease and severe hemodynamic impairment— Atrial arrhythmias are often poorly tolerated in patients with postsurgical congenital heart disease. As a consequence, the goal of therapy should be rhythm control rather than rate control, whenever possible.

Catheter ablation probably represents the treatment of choice for atrial tachycardia in this population in whom antiarrhythmic therapy often proves unsatisfactory. Antiarrhythmic therapy may also carry risks in patients with associated abnormalities in sinus or AV node conduction, those with ventricular dysfunction, and those prone to associated electrolyte disturbances.

When such patients require surgical treatment for associated structural abnormalities, it may be reasonable to consider intraoperative ablation to target such abnormalities. However, multiple potential circuits may be responsible for arrhythmias in such patients, which may involve regions of slow conduction related to the cavo-tricuspid valve isthmus, an atriotomy scar, abnormal conduction across the crista terminalis, and reentry around an atriotomy patch. It is therefore often advisable to perform electrophysiology study and detailed mapping and RFCA preoperatively. When appropriate, additional intraoperative cryoablation to consolidate RFCA lesions might be considered.

While RFCA should be considered early in the course of treatment for atrial tachycardias, there is less experience to guide the optimal timing (or technical approach) for atrial fibrillation in adult congenital heart disease (ACHD) patients. However, it is important to recognize that atrial tachycardia is often incorrectly characterized as atrial fibrillation due to the frequent absence of classic “flutter” waves and frequently variable ventricular response. If the diagnosis is unclear, it is important to perform electrophysiologic testing to attempt induction and characterization of the tachycardia mechanism, especially before contemplating on RFCA to target atrial fibrillation (as occurred in this case) or surgical maze procedure.

• 2.
  

  Antiarrhythmic treatment for prevention of atrial arrhythmias —When antiarrhythmic therapy is contemplated, the choices for atrial arrhythmias in adult CHD patients may include Class I agents (flecainide or propafenone) or Class III agents (sotalol or dofetilide, dronedarone, amiodarone).

In many instances, it may be necessary to slow the ventricular response with the addition of a β-blocker or a calcium channel blocker. This may be especially important in the ACHD patients whose atrial rates tend to be slower than typical atrial flutter and may display more robust AV node conduction, predisposing them to 1:1 AV conduction during tachycardia.

Class IC agents probably carry increased risk for those patients with impaired ventricular function as well as those with associated (recognized or occult) coronary artery disease and should be avoided in such patients. Because they slow conduction velocity and thus prolong the tachycardia cycle length, they slow the tachycardia in the atrium, which can lead to conduction of more beats to the ventricle (thus, for example, a patient with an atrial rate of 300 with 2:1 block would have a ventricular rate of 150, whereas slowing the atrial rate to 200 could lead to 1:1 conduction and a ventricular rate of 200, which would be less well tolerated by the patient).

Class III agents are therefore generally preferred in ACHD patients, acting to prolong refractoriness and thus limit the excitable gap of the reentrant circuit without substantial effect on the atrial rate itself. However, sotalol may be poorly tolerated in patients with moderate-severe ventricular dysfunction or those with impaired AV conduction, and dofetilide may be a preferred choice in such cases. Dronedarone is not recommended in patients with congestive heart failure or significant ventricular function due to concerns of increased mortality.

Amiodarone may offer the best potential for efficacy but carries the potential for side effects including thyroid dysfunction, pulmonary fibrosis, and hepatotoxicity with long-term use.

In selected patients with infrequent tachycardia episodes, there may be a role for episodic (“pill-in-the-pocket”) therapy. This might include administration of oral diltiazem at first onset of symptoms to limit AV conduction while patients seek medical attention (it must be explicitly explained that this is a short-term temporizing measure only, and attenuation of symptoms should not be presumed to reflect tachycardia termination). Additionally, successful termination of atrial tachycardia with acute oral administration of sotalol has been described.

• 3.
  

  Indications for oral anticoagulation and eventual use of new oral anticoagulants— Although some data exist in the ACHD population, the role for chronic anticoagulation in ACHD patients with atrial arrhythmias is largely extrapolated from the extensive body of data for stroke prevention in adults with atrial fibrillation. However, there may be important differences. Many (but not all) ACHD patients may be acutely aware of the onset of their tachycardia. In such patients, it may be reasonable to forego chronic anticoagulation and begin anticoagulation with a newer anticoagulation agent at the onset of symptoms (possibly concurrent with an agent to slow AV conduction). However, such an approach may be inappropriate in patients who have previously presented with atrial tachycardia discovered incidentally during routine evaluation or when presenting with hemodynamic deterioration without acute palpitations. Likewise, the addition of a chronic AV-slowing agent may hinder the patient’s recognition of future tachycardia recurrences.

Although adult studies suggest improved safety and efficacy of the newer oral anticoagulants compared with warfarin, there are limited data in their use in ACHD patients. The most recent consensus statement in ACHD patients suggested warfarin remains the standard therapy but acknowledged the newer agents might be considered in patients with simple forms of CHD and no significant valve disease or mechanical valve. However, experience is being accrued, and multicenter collaborative efforts are underway to review the experience of these agents in ACHD patients.

• 4.
  

  Indications for surgical ablation for atrial tachycardias—The role for surgical ablation rather than catheter ablation is dependent on multiple factors, including the patient’s anatomy, the operation being planned, the institutional experience of the surgical and ablation teams, and the availability of intracardiac mapping and other advanced intraoperative techniques such as hybrid epicardial-endocardial approach. As noted earlier, if surgical ablation is contemplated, it is often advisable to perform preoperative electrophysiology study and mapping to better define the region or regions to be targeted. In the case of Fontan conversion to extracardiac conduit, intraoperative cryoablation should be routinely performed, although the best placement of cryolesions may vary according to the anatomy and type of previous Fontan connection. Although the approach pioneered by Mavroudis and Deal included a Cox III maze targeting atrial fibrillation, there are little data to support routine preemptive treatment of atrial fibrillation at the time of Fontan conversion. The potential impairment of left atrial transport function with this approach and adverse consequences on the Fontan circulation may represent a more significant concern than late presentation with atrial fibrillation. Indeed, while there may be a notion that Fontan revision represents the “last chance” to intervene due to loss of direct vascular access to the atria, experience is growing in ablation after ECC-Fontan.

  
  
• 5.
  

  Rate control of atrial arrhythmias versus rhythm control in patients with congenital heart disease —As noted earlier, patients with ACHD may be more prone to hemodynamic compromise due to their arrhythmias, making rate control an unattractive option. This can be the result of overt issues such as residual structural impairments (e.g., as semilunar or AV valve dysfunction) or the adverse impact on passive transpulmonary flow in the Fontan circulation with loss of 1:1 AV synchrony. In other instances, even patients with a seemingly good surgical result may suffer occult diastolic dysfunction, affecting their ability to tolerate their arrhythmia. Congestive heart failure may develop chronically or even acutely in ACHD patients in whom seemingly effective rate control has been maintained. Thus, rhythm control is usually preferable, ideally by catheter ablation alone, or in combination with antiarrhythmic therapy or antitachycardia pacing when appropriate.