Ebstein Anomaly After Tricuspid Valve Replacement Needing Pacemaker Implantation: Case submitted by Christopher J. McLeod, MBChB, PhD

Consultant Opinion #1

Narayanswami Sreeram, MD

Daniel Steven, MD

The patient presents with symptomatic bradyarrhythmia. The ECG and Holter traces confirm episodes of sinoatrial exit block and high-grade AV block. In association with the frequent episodes of near syncope, the indication for implantation of a permanent pacemaker seems given.

Progressive conduction system disease is part of the disease process in a variety of structural heart lesions, including Ebstein anomaly, and may be inherent to the disease or acquired as a result of multiple surgical procedures. Our patient has undergone previous surgery for tricuspid valve regurgitation and a surgical right atrial maze procedure. The commonest indications for permanent pacing in adults with structural heart disease are sinus node dysfunction and AV block acquired outside the acute surgical setting. Our patient appears to have developed both these pathologic conditions. It is possible that the intra-atrial block, resulting in part from the previous right atrial maze procedure, may be masquerading as an episodic AV block as seen on the Holter recording. This, however, should not influence the choice of permanent pacemaker but necessitates implantation of a ventricular lead.

The choice of optimal technique and the route for permanent pacing in this patient are complicated by three factors: Ebstein anomaly with a history of surgery and evidence of persistent RV dysfunction, a bioprosthetic tricuspid valve, and its implanted location upstream from the coronary sinus. Patients with operated structural heart disease and residual hemodynamic sequelae benefit from retaining AV synchrony, necessitating the consideration of a dual chamber pacing system in this patient. In general, it is preferable not to have a permanent pacing lead passing through the prosthetic valve in order to prevent the development of unacceptable tricuspid valve insufficiency (which was likely the primary indication for bioprosthetic tricuspid valve implantation in this patient). This is particularly important in the setting of Ebstein anomaly, where RV function is likely to remain compromised, regardless of previous surgical repair. A possible option in the setting of replacement of the tricuspid valve in a patient with a preexisting endocardial ventricular pacing lead would have been to allow the lead to be placed exterior to the sewing ring of the valve, but this was not a consideration here, as the patient did not have symptomatic bradyarrhythmia or a preexisting endocardial pacing lead at the time of valve surgery.

In the recent years, there has been considerable controversy regarding the optimal ventricular pacing site. Several large studies in adults and children have established that chronic RV pacing is associated with LV dyssynchrony, dysfunction, and structural alterations in the LV that may be progressive. Although this is probably of particular importance to children, who will require lifelong pacing over several decades, several studies have established that a relevant proportion of patients with Ebstein anomaly have preexisting structural and functional abnormalities affecting the LV. Structural alterations include LV noncompaction, mitral valve prolapse, and LV fibrosis. Both systolic and diastolic dysfunction of the LV have been reported in Ebstein anomaly, and some of these functional alterations persist and may progress despite surgical procedures in the right side of the heart. The ideal pacing technique would therefore be dual chamber pacing with a right atrial and a LV lead. In this patient, access to the coronary sinus, and therefore the possibility of transvenous LV pacing, is precluded by the location of the tricuspid valve bioprosthesis. Permanent pacing would therefore have to be accomplished by the use of an epicardial LV lead, accepting the fact that epicardial systems are less durable and have a shorter lifespan than transvenous systems. The choice of location for the atrial lead also needs to be carefully considered. Owing to the previous surgical procedures (right atrial maze and tricuspid valve replacement), there is a considerable risk that poor atrial thresholds may be obtained from epicardial atrial sites caused by scar tissue from prior surgery. It may be necessary therefore to implant an endocardial atrial lead in combination with the epicardial LV pacing lead.

Permanent pacing in adults with structural heart disease also presents unique problems, both procedure related and at follow-up. Surgical access is likely to be more complicated, and the incidence of acute complications such as bleeding, pocket infection, and pneumothorax is higher. Failed or difficult lead placement is common in this setting, with increasing difficulty being associated with a higher number of prior surgical procedures. Such procedural difficulties and failures occur more frequently in Ebstein anomaly than in other structural lesions. Late complications such as early battery depletion, pacemaker migration, and erosion are also more frequently observed in the setting of permanent epicardial pacing in this patient population.

Lead failures, defined as a failure to reliably capture or sense the ventricle or atrium, and lead dislodgement or fracture are commonly encountered with epicardial ventricular leads. The presence of Ebstein anomaly has been noted to be an independent risk factor for lead failure in one study, regardless of epicardial or endocardial location and whether the lead was implanted in the RV or LV. It has been suggested that this may be a unique feature of this anomaly and may be the result of an inherent tendency to fibrosis around the lead tip at the site of implantation.

In summary, the rather unique postsurgical anatomy of this patient necessitates the choice of a suboptimal dual chamber pacing system, with an anticipated higher rate of acute and follow-up complications. A final consideration would be the transvenous implantation of a leadless single chamber pacemaker. There are few reports on the use of such a system in adults with complex structural heart disease and little follow-up data on their performance in this patient population. There is a small risk of cardiac perforation, and this may be relevant in the setting of Ebstein anomaly and a thinned-out RV. Considering that the patient is still relatively young and fit, this would not be the procedure of choice but may be considered in the future.

Consultant Opinion #2

Henry Chubb, MBBS, PhD

Eric Rosenthal, MD FRCP