Consultant Opinion #1

Jeremy Moore, MD

This is an interesting case with several important EP considerations unique to the ACHD population, specifically to those with DTGA palliated by the Mustard or Senning operation. The first issue to be examined is the unexplained development of severe biventricular dysfunction in this patient, with the possible contribution of an undiagnosed supraventricular tachycardia. The phenomenon of tachycardia-induced cardiomyopathy is well described and is a fully reversible form of congestive heart failure. This process is characterized by incessant or nearly incessant tachycardia with the insidious progression of heart failure. Although there are no systematic studies of tachycardia-induced cardiomyopathy in the ACHD population, anecdotally, these cases usually stem from initially subclinical atrial arrhythmias such as intra-atrial reentrant tachycardia or atrial fibrillation. Although certainly incessant or nearly incessant AVNRT could in theory result in cardiomyopathy, this form of tachycardia tends to be paroxysmal in nature and rarely leads to cardiomyopathy. On the other hand, supraventricular arrhythmia that arises as a result of ventricular dysfunction is well described in the ACHD literature. Because AVNRT and progressive ventricular dysfunction are both common after surgically repaired DTGA, it is likely that the AVNRT discovered in this patient is an incidental finding.

The second issue here is this patient’s need for an ICD. Sudden death risk following the DTGA Mustard or Senning operation is one of the highest in the ACHD population, equaling approximately 0.5% per patient-year. The risk tends to be bimodal with an early peak after repair, followed by a second peak in adulthood that corresponds with the progressive decline in systemic RV function. Risk factors are multiple and include atrial tachyarrhythmia, ventricular dysfunction, tricuspid regurgitation, increasing age, and electrocardiographic findings such as QRS duration (140 ms serving as a useful discriminant value). Unlike other forms of congenital heart disease, there is limited utility for programmed stimulation in the risk stratification process. Importantly, β-blocker administration has been shown to be protective against sudden cardiac death in this population.

Currently, the only available guidelines for ICD placement in the setting of DTGA after Mustard or Senning operation are a result of expert consensus, generally supported by limited clinical evidence. Such guidelines suggest that ICD therapy may be reasonable with an RVEF <35%, especially if accompanied by additional risk factors such as complex ventricular arrhythmias, unexplained syncope, NYHA functional class II or III symptoms, QRS duration ≥140 ms, or severe systemic atrioventricular (AV) valve regurgitation.

An important consideration when planning ICD placement for patients with congenital heart disease is the presence of an intracardiac shunt, which can as much as double the rate of systemic thromboembolism after implantation. Also, the presence of severe pulmonary hypertension with subsequent mitral regurgitation can result in further clinical deterioration. In either of these scenarios, S-ICD could be considered to avoid potential complications associated with conventional ICD. Importantly, lack of bradycardia pacing and cardiac resynchronization therapy (CRT) capability is an important limitation to S-ICD, and this especially applies to the present case where both the functionalities may be important.

The final issue is the risks versus benefits of CRT in this situation. CRT for congenital heart disease has been shown to be beneficial in many circumstances. Patients with chronic ventricular pacing are most likely to benefit, in whom the electrical delay is, in part, iatrogenic and ubiquitous. For others, especially those with systemic RV morphology as in the present case, the benefits of CRT are less clear. Although mechanical dyssynchrony as observed by echocardiography is extremely common among patients with DTGA after a Mustard or Senning operation, CRT is of limited to no use unless accompanied by markers of electrical delay. For this reason the QRS duration is of paramount importance. Current guidelines emphasize complete right bundle branch block with a QRS duration of at least 150 ms before contemplation of CRT for these patients. This degree of QRS prolongation has been shown to be present in approximately 7% of ACHD patients with DTGA after Mustard or Senning operation and thus may apply here.

Importantly, CRT is necessarily invasive in the DTGA group as the coronary venous system draining the systemic RV is rarely, if ever, accessible by the transvenous route. Most centers prefer to place a dual chamber pacing system first, followed by an epicardial lead for resynchronization of the RV. The epicardial lead is typically placed on the RV free wall via a right thoracotomy. Ideally, the epicardial lead is placed at the site of the latest RV activation. This can be assessed at the time of pacemaker implantation by 3D mapping or alternatively in the operating room with a roving electrode. A more empirical, anatomic approach in which the lead is placed directly across the tricuspid valve annulus when the valve is viewed en face may achieve the widest separation in the two ventricular leads and optimal resynchronization performance.