Consultant Opinion #1

Ronald Kanter, MD

I will attempt to address the questions in the order provided. Following atrial switch operation, the incidence of RV dysfunction leading to heart transplantation is 20% at 20 years, and this seems to apply to both simple transposition and those having associated lesions. Although the etiologies may include chronic atrial tachyarrhythmias or, as in this patient, myocardial infarction, more often, the cause is not known. Tricuspid valve regurgitation with secondary volume overload is often contributory. Although occasionally there are structural abnormalities of the valve or papillary muscle infarction, improvement in valve function can be expected as ventricular function improves.

• 1.
  

  What is the role of biventricular pacing for a patient of this nature when they present with systemic RV failure?

The contribution of intraventricular dyssynchrony of the systemic right ventricle to systolic dysfunction in this patient group has recently been demonstrated. Dyssynchrony and electromechanical delay, especially of the free wall, has been shown to correlate with myocardial fibrosis of the systemic right ventricle. Speckle tracking of the right ventricle has identified the “classic pattern” of dyssynchrony in a handful of Mustard patients who subsequently clinically benefitted from cardiac resynchronization therapy (CRT). This approach seems especially applicable in the presence of severe intraventricular conduction delay with a QRS duration >140 ms, either due to intrinsic delay, or—as in this case—related to left ventricular pacing.

The technique for CRT in these patients nearly always requires a limited right thoracotomy or sternotomy for access to the epicardial surface of the systemic right ventricle. The lead should be placed near the acute angle, just anterior to the tricuspid valve. We prefer a hybrid approach with a transvenous lead to the left ventricle. This eliminates the need for extensive surgical dissection to place a left ventricular lead. As is true in patients having structurally normal hearts, lead placement as close to the base of the heart is desirable so as to accomplish maximal lead separation. Because this patient had had a myocardial infarction, identification of a nonviable ventricular wall is necessary in order to avoid ventricular lead placement onto electrically inactive tissue. This may be accomplished by either radionuclide or electromechanical techniques.

• 2.
  

  In cases of SVT or atrial tachycardia, what are the first-line therapies? Is antitachycardia pacing a first-line therapy or should he have been tried on other treatment modalities such as medications or ablation first?

First-line therapy for intraatrial reentry tachycardia (IART) should be guided by the clinical context, although, in general, a recently published consensus statement favors ablative therapy over antiarrhythmic drugs (Class IIa).

Because this patient required bradycardia pacing for both sinoatrial node dysfunction and impaired AV conduction, a pacing system having atrial antitachycardia pacing capability was a reasonable—and safe—first approach. However, antitachycardia pacing has the potential for conversion of the index tachycardia into a different one. In atrial switch patients having normal AV conduction, this could result in an unpredictable and potentially faster ventricular response, even leading to ventricular tachycardia and death. Whenever possible, we only program atrial antitachycardia pacing in patients whose system also has ventricular defibrillation capability.

Antiarrhythmic drugs have limited efficacy (e.g., AV nodal blocking agents), dangerous proarrhythmic potential (e.g., class IC, III agents), or undesirable long-term noncardiac side-effects (amiodarone). That said, sotalol is a reasonable first therapeutic option, followed by dofetilide, although amiodarone is also considered a reasonable second-line drug (Class IIa recommendation).

Catheter ablation for IART may be successfully accomplished in over 85% of patients. Although the recurrence rate is greater than that seen following IART ablation in patients who are postrepair of tetralogy of Fallot or atrial septal defects, it is not as high as in patients who have undergone Fontan-style operations. AV nodal reentrant tachycardia and focal atrial tachycardia are also encountered in these patients and are also highly responsive to catheter ablation. The majority of tachycardia substrates requiring ablation are located in the pulmonary venous atrial side of the circulation. Catheter courses requiring both retroaortic valve/retrotricuspid valve and transbaffle techniques have been well described.

• 3.
  

  What are the ways to deal with systemic baffle obstruction prior to placing leads? Does the concern for baffle obstruction preclude lead placement?

In general, whenever a patient who has undergone surgery for congenital heart disease (CHD) is determined to require transvenous placement of conduction hardware to treat bradycardias or tachycardias, meticulous evaluation of postsurgical intracardiac anatomy is required in advance. In no circumstance is this more relevant than in post-Senning and (especially) post-Mustard patients. Atrial baffle obstruction and/or residual baffle leaks exist in as many as half of these patients, particularly in the Mustard group. These residual problems should always be addressed prior to placement of transvenous leads. We have seen patients in whom leads were placed across stenotic baffles with resultant SVC syndrome or new onset of cyanosis due to right-to-left shunting across unappreciated proximal baffle leaks. Superior systemic venous baffle obstruction is more common than either inferior systemic or pulmonary venous baffle obstruction, making this issue especially pertinent to the implanting electrophysiologist. Total obstruction may be present in asymptomatic patients due to decompression of upper body venous return down the azygos vein. In general, we recommend dilatation and (usually) stent placement if the narrowest cross-sectional area (as determined by careful MRI-, echocardiography-, or venography-guided measurements) is less than twice that of the combined cross-sectional area of the leads to be used. Even total obstruction over a short segment can be recanalized and stented by the interventionalist, so that leads may be placed. Residual baffle leaks result in left-to-right shunts and may not be evident by transthoracic echocardiography. Cardiac MRI or transesophageal echocardiography is usually required for detection and precise localization. Placement of leads, especially atrial, in the presence of such a defect places the patient at risk for paradoxical embolization. Once identified, the interventionalist can occlude the defect using occluder devices or covered stents. Two additional caveats are as follows: (1) Before the interventionalist places a stent in an atrial baffle in these patients, evaluation for IART should be performed. Although most IART substrates are in the inferior portion of the atrial mass and most obstructions and baffle leaks are in the superior portion, once a stent is placed—especially a covered stent—catheter access to the IART substrate may be rendered impossible. (2) Coordination between the electrophysiologist and the interventionalist is crucial in these cases. Anatomic details should be discussed in advance. For example, although the interventionalist may wish to implant a superior baffle stent quite inferiorly into the systemic venous atrium, this may impede the ability to place an atrial lead. Liberal flaring of the inferior portion of that stent will help avoid chronic lead damage. The interventionalist and electrophysiologist together should be able to rehabilitate the anatomy and place device hardware in nearly all of these patients.

Also, pertinent to the patient presented, baffle obstruction may be observed in the presence of chronically implanted leads. Balloon dilatation may be attempted in these patients, so long as lead functionality is assessed immediately afterward. However, stents should never be placed in such situations. That is, jailing of chronic leads is poor practice because it is then impossible to extract those leads, should the patient develop endocarditis. Open heart surgery would be the only way to remove potentially infected hardware. If baffle stenosis has become a clinical problem in a patient having transvenous leads, the better practice is lead extraction, treatment of obstruction, and lead replacement.

• 4.
  

  What is the place of S-ICD therapy in patients with a Mustard operation? Should the presence of prior devices be considered a potential problem in patients being evaluated for S-ICD?

There is increasing experience with implantation of the S-ICD in patients with CHD. Patient eligibility for S-ICD requires that their surface QRS-T complex conforms to one of several predetermined templates in at least one of three lead configurations and in lying and standing positions. In patients having CHD, the eligibility failure rate is higher (21%) than in those having a normal heart, but eligibility may be improved (from 79% to 88%) by placing right (compared with left) parasternal surface leads (and, hence, a right parasternal subcutaneous lead). Once placed, S-ICD systems appear to be as effective in congenital heart patients as in those with normal hearts. In Moore’s report of 21 patients, two had undergone the Mustard operation. The compatibility of an S-ICD with a preexisting transvenous bradycardia system, as in the patient presented, is established in patients having a normal cardiac anatomy. Eligibility in those having normal heart anatomy seems to be influenced by permanent RV lead placement, with apical lead placement having a lower eligibility rate than septal or biventricular sites. In the presence of CHD and ventricular pacing, eligibility seems to be reduced, although again, placement of a right parasternal lead may improve the eligibility rate. In Okamura’s report, eligibility was negatively impacted by inverted T waves in leads V2–V6 or a long QTc interval. In a small series of four patients having CHD and bradycardia pacing systems, successful implantation, defibrillation threshold testing, and device function were demonstrated. This experience even included a patient having a unipolar lead. Those authors recommended programming the upper tracking rate to less than one half the S-ICD’s tachycardia detection zone in order to prevent inappropriate therapy due to double sensing (pacing spike and QRS). We would be very wary of placing an S-ICD in the presence of any unipolar pacing system.