11
How to Ablate Accessory Pathways in Patients with Ebstein’s Syndrome
Christina Y. Miyake, MD, MS
Introduction
The highest incidence of accessory pathways (APs) and arrhythmias among patients with congenital heart disease occurs among those with Ebstein’s anomaly. Catheter ablation in this group of patients tends to be more difficult than in those with structurally normal hearts, and although cases may be straightforward, they can make for a long and difficult day. Hemodynamic instability during tachycardia, low-frequency and fragmented signals, difficulty locating and maintaining stability on the tricuspid annulus, and multiple pathways are just some of the challenges that may arise.
A survey of experts across the country who have been performing ablations in Ebstein’s patients for years revealed there is no single best approach to these patients. However, all would agree that despite advances in technology and imaging capabilities, success is dependent on a good understanding of basic electrophysiology (EP) and the ability to interpret intracardiac signals. This chapter will briefly review Ebstein’s anatomy, its effects on the conduction system, and helpful techniques when bringing a patient to the lab for ablation.
Anatomy of Ebstein’s Anomaly
Ebstein’s anomaly is due to failure of the septal and posterior leaflets of the tricuspid valve to delaminate from the right ventricle (RV) endocardium. This results in apical displacement of the effective valve opening or hinge point and a relative decrease in the size of the functional RV (Figure 11.1; 
Video 11.1). The area between the true tricuspid valve annulus, which remains in the normal position at the atrioventricular groove, and the displaced tricuspid valve is referred to as the “atrialized” portion of the RV (Figure 11.2). This atrialized RV myocardium becomes relatively thin-walled under atrial- rather than ventricular-level pressures. While the septal and posterior leaflets may be dysplastic or deficient, the anterior leaflet is often large and “sail-like” and may cause obstruction of the RV outflow tract (Figure 11.3). Patients may have other coexisting cardiac anomalies, most commonly ventricular septal defects and pulmonary stenosis.
Figure 11.1 Displacement of the tricuspid valve leaflets. (Image courtesy of Dr. Norman Silverman and Dr. Robert H. Anderson.)
Figure 11.2 Displacement of the tricuspid valve results in an atrialized portion of the RV. (Image courtesy of Dr. Norman Silverman and Dr. Robert H. Anderson.)
Figure 11.3 Anatomical specimen demonstrating displacement of the septal and posterior leaflets of the tricuspid valve. The septal leaflet is deficient. The anterior leaflet hinges at the annulus but is large and “sail-like.” (Image courtesy of Dr. Norman Silverman and Dr. Robert H. Anderson.)
The hemodynamic effect of Ebstein’s anomaly varies depending on the severity of tricuspid valve displacement and the competency of the tricuspid valve. Although some infants require early surgical intervention, a majority of individuals do not require any intervention for years. Over time, however, tricuspid regurgitation leads to atrial and ventricular enlargement, widening of the tricuspid valve annulus, and possible right-to-left shunting (a majority of patients will have an atrial-level communication consisting of a patent foramen ovale or a secundum atrial septal defect). The reduced functional RV cavity along with tricuspid regurgitation results in retardation of forward blood flow and cyanosis, which can lead to hemodynamic instability and even syncope in patients who develop arrhythmias.
Effects of Valve Displacement on the Conduction System and Associated Arrhythmias
Displacement of the tricuspid valve leads to separation of the valve hinge point from the AV node. While conduction through the AV node is generally maintained, this displacement may lead to bridging myocardium and an increased incidence of atrioventricular APs. It is thought that approximately 30% of Ebstein’s patients have paroxysmal SVT, with 20% having manifest bypass tracts; however, the true incidence of APs is unknown.1,2 Among those with APs, 30 to 50% will have multiple pathways.3,4 Nearly all APs found in Ebstein’s patients will be right sided, with a majority located in the posterolateral to posteroseptal location. The exception is the congenitally corrected transposition with an Ebsteinoid left-sided systemic tricuspid valve. The APs have typical nondecremental, “all or none” conduction properties; however, the presence of intra-atrial, infranodal, and atrialized RV conduction delays can result in (1) minimal preexcitation patterns on ECG, and (2) longer PR/AV or VA times at baseline and during tachycardia. Atriofascicular pathways (so called Mahaim fibers) can also be seen in this population but are less common.
SVT can occur for several reasons. Younger patients with SVT most commonly have AP-mediated tachycardia. With age, atrial dilation can lead to atrial flutter, intra-atrial reentrant tachycardia, and atrial fibrillation. VTs can also occur in this population.
Displacement of the tricuspid valve also results in fibrosis of the right-sided His-Purkinje system (HPS), resulting in 75 to 80% of Ebstein’s patients with a right bundle branch block (RBBB) pattern on their ECG.
How to Decide Which Patients to Bring to the EP Laboratory
There are no specific guidelines to determine which patients require an EP study (EPS); however, recent data suggests that a majority of Ebstein’s patients scheduled for surgical repair have substrates for supraventricular and ventricular arrhythmias at EPS.10 For patients scheduled for surgical repair to address their Ebsteinoid valves, arrhythmias in the postoperative period increase patient morbidity and mortality. Furthermore, surgery on the tricuspid valve can result in future inability to access the annulus or isthmus by transcatheter approach. Therefore, patients who are scheduled for surgery with any history of palpitations, concern for a possible AP, or manifest preexcitation on ECG should be evaluated with a formal EPS prior to surgery. While the risk of an AV in asymptomatic patients without preexcitation is low, consideration for an EPS should be given due to the risk of nonaccessory pathway-mediated arrhythmias including atrial and ventricular tachycardias.10
The general consensus suggests that the following patients should be evaluated by an EP study:
1. All patients undergoing surgical repair
1. Patients with manifest preexcitation on ECG
1. Symptomatic patients
Preprocedural Planning
Patients should have a complete preprocedural evaluation, including an ECG, echocardiogram, and a full physical exam, including oxygen saturation and an evaluation by a cardiac anesthesiologist. Previous records should be reviewed, including any prior cardiac surgeries, catheterizations, and imaging studies. Further imaging, such as CT or MRI scan, is not required; however, if the patient has had a recent study, prior review of these images is generally helpful. Operative notes should be reviewed for sites of surgical incisions and procedures performed on the tricuspid valve. Vessel occlusions noted on imaging studies or prior catheterizations should be identified. At our center, we generally perform a right-sided hemodynamic catheterization on all Ebstein’s patients coming in for an EP study.
An informed consent should be obtained from patients for angiography, including selective coronary injection, in addition to the EP study. Risks of possible injury to the coronary artery should be discussed. If assistance is required by a catheterization interventionalist, this should be arranged in preparation for the procedure. Patients should be instructed to discontinue any antiarrhythmic medication for 5 half-lives prior to the procedure.
Most patients can be discharged home the same day. However, patients with severe disease, baseline cyanosis, polycythemia, and poor hemodynamics may not tolerate prolonged anesthesia, contrast injections, and long periods of tachyarrhythmia. Consideration for postprocedural care in an intensive care unit should be given.
ECG
Patients with right atrial enlargement may demonstrate tall P waves or first-degree AV block. The ECG should be examined for evidence of a manifest AP. Conduction delays both through the HBs and through the atrialized RV may lead to very subtle preexcitation patterns, making this difficult. However, a majority of patients, regardless of the degree of tricuspid valve displacement, have an incomplete or complete RBBB pattern (Figure 11.4). The lack of an RBBB pattern is not diagnostic but should raise suspicion for a manifest pathway, particularly if there is a short P-R interval (Figure 11.5, A–C).5 A symptomatic patient with a normal P-R interval may have a concealed pathway or a Mahaim fiber (particularly if there is a left bundle branch block [LBBB]). ECG preexcitation patterns can be helpful to determine right- versus left-sidedness6 but should not be used to determine definitive pathway location; however, negative delta waves in the inferior leads generally correspond to bypass tracts in the posteroseptal location.
Figure 11.4 Example of typical ECG seen in patients with Ebstein’s anomaly. There is RBBB pattern.
Figure 11.5 Examples of ECGs demonstrating manifest accessory pathways. Note the lack of RBBB pattern on each of these ECGs.
Echocardiogram
An echocardiogram is obtained in all patients as part of the preoperative evaluation. Visualization of the degree of tricuspid valve displacement, amount of tricuspid regurgitation, presence of outflow tract obstruction, size of the RA and RV, and the presence and size of atrial septal communications can be helpful prior to mapping. Overall ventricular systolic function should also be assessed.
Physical Exam
A patient’s hemodynamic status is important to assess prior to the procedure. A full physical exam should be performed. Elevated jugular venous pressures, hepatomegaly, and peripheral edema are signs of right-sided heart failure and should be taken into account, as some patients may not hemodynamically tolerate the procedure. Baseline desaturation, creatinine, and evidence of polycythemia should also be noted.
Procedure
Patient Preparation
At our center, all patients, regardless of age, are placed under general anesthesia by cardiac anesthesiologists. Particularly in the younger patients, where cardiac structures are small and ablation catheters are relatively large, it is important to eliminate the risk of sudden catheter movement.
Access
Known vessel occlusions should be determined prior to the patient entering the lab. Patients with Glenn procedures will not have access via the SVC. At least 4 sheaths should be placed for standard recording catheters, to be initially located in the high right atrium (HRA), HB position, right ventricular apex (RVA), and CS. Consideration should be given for placement of a 4-Fr sheath into a femoral artery prior to heparin administration. This sheath can be used to monitor hemodynamic status during the case and can be used to take coronary angiography if needed later in the case. In patients with manifest preexcitation, it can be helpful to have a HRA pacing catheter during mapping and ablation, but this requires an additional venous sheath.
Anticoagulation
The use of heparin varies between centers and individual operators. At our center, due to the high incidence of atrial-level communications and relatively higher risk of right-to-left shunting in this population, we give all patients heparin (100 U/kg, maximum 5000 U) prior to insertion of any catheters and maintain the ACT > 200 seconds. Patients are also discharged on 2 to 3 months of low-dose (81 mg) aspirin daily.
Selection of Guiding Sheaths and Catheters
If catheter stabilization is a problem, long sheaths should be used. In particular, Swartz sheaths (St. Jude Medical Inc., St. Paul, MN) for the posteroseptal (SR0), lateral (SR4), anterolateral (SR3), and anterior (SR2) positions can be helpful. For posterior or posterolateral, try a Mullins Introducer Sheath (Medtronic Inc., Minneapolis, MN). The Agilis steerable sheath (St. Jude Medical Inc., St. Paul, MN) can be used for any position. For pediatric patients, a limited selection of reduced-radius Swartz sheaths are available but generally target only the anterolateral (SRR3) and lateral (SRR4) positions.
Tricuspid Valve Anatomy
The tricuspid annulus is thinner than the left AV groove and is often incomplete. The annulus may also be dilated, and tricuspid regurgitation can be severe. This can make catheter stabilization and tissue contact a challenge. Although annular signals can sometimes be normal, often these signals are low frequency and fragmented, making it difficult to differentiate between atrial and ventricular EGMs (Figure 11.6). Use of 3-dimensional (3D) electroanatomical mapping systems can be helpful; however these systems rely on use of electrograms to identify the tricuspid annulus. In an Ebstein’s patient with fragmented annular signals, this may pose challenges when trying to identify the tricuspid annulus. If locating the tricuspid valve annulus becomes an issue, there are several things that can be attempted (Table 11.1).
Figure 11.6 Preablation recordings during sinus rhythm in a patient with Ebstein’s anomaly and a manifest right posterolateral AP. Surface ECG lead II and local EGMs from 4 sites along the tricuspid annulus can be seen. Note abnormal ventricular (V) EGMs extending from the posteroseptal (R postsept) to the posterior (R post) and posterolateral (R postlat) regions. Normalization of V EGM is observed in the lateral (R lat) region. A indicates atrial EGM; AP, presumed AP activation potential; and Δ, onset of delta wave. (Reprinted with permission from Cappato R, et al. Circulation. 1996;94:376–383.)
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
