Accessory pathways in Ebstein's Anomaly

Raja Selvaraj
Professor of Cardiology
JIPMER

Tricuspid valve leaflets form during weeks 5–8 of gestation via delamination (undermining and peeling of inner RV myocardium) (4)
In Ebstein’s, delamination fails for the septal and posterior leaflets (1,4)
Leaflets remain adherent to the underlying RV myocardium → pulled downward, cannot attach to true annulus (1)
Anterior leaflet may be partially delaminated but is often enlarged (4)
Genetic triggers: deletions in NKX2.5, TBX5; environmental: maternal lithium exposure (5)

Ref:

van Son JA, et al. Morphogenetic considerations on congenital malformations of the tricuspid valve. J Thorac Cardiovasc Surg 1995;110:1346‑1359.
Postma AV, et al. Mutations in the sarcomere gene MYH7 in Ebstein anomaly. Circ Cardiovasc Genet 2011;4:43‑50.
Attenhofer Jost CH, et al. Ebstein’s anomaly. Heart 2007;93:530‑536.

Disorder of molecular signaling pathways ?

Accessory pathways in Ebstein's

APs in Ebstein’s are almost exclusively right‑sided (≈95% of cases) (7)
Most common location: right posteroseptal region (40–50%) (9)
Second most common: right free‑wall (30–40%) (9)
Anteroseptal and left‑sided APs are rare (each <5%) (7,9)
Multiple APs (≥2) occur in 30–50% of Ebstein patients with pre‑excitation (8,9)
Both manifest (anterograde conduction) and concealed (retrograde‑only) pathways are seen; concealed pathways account for 20–30% of all APs (7,8)

Image: 30 year data from Boston Childrens hospital. 76 patients, 61 with AP Multiple APs in 25%, only 3 were atriofascicular Recurrence in 35%, more common in younger children

Ref:

Iturralde P, et al. J Cardiovasc Electrophysiol 2005;16:6‑11.
Reich JD, et al. J Am Coll Cardiol 1998;31:463‑468.
Obeyesekere MN, et al. A practical approach to the diagnosis and management of Ebstein’s anomaly with pre‑excitation. Heart Rhythm 2012;9:1154‑1160.

El-Assaad I, DeWitt E, Mah D …John K. Triedman, Edward P. Walsh. Accessory pathway ablation in Ebstein anomaly: A challenging substrate. Heart Rhythm, 2021; 18, 1844-1851

Ebsteins anomaly and accessory pathways

Every patient with Ebstein's anomaly needs an ECG to assess for presence of accessory pathways
Every patient with Ebstein's anomaly even when asymptomatic and without preexcitation should have an EP study before surgical repair

Need for preoperative EP study

Preexcitation can be subtle
Accessory pathways can be concealed
Other arrhythmias can occur
- IART
- VT
Perioperative arrhythmias are poorly tolerated
Ablation may be more difficult after surgery

Pre op screening

Shivapour J, Sherwin E, Alexander M … Edward P. Walsh. Utility of preoperative electrophysiologic studies in patients with Ebstein’s anomaly undergoing the Cone procedure Heart Rhythm, 2013; 11, 182-186

Is there preexcitation ?

Absence of RBBB

Challenges in mapping

Anatomic abnormalities - displaced annulus, ridge
Broad pathways, epicardial pathways
Signals from atrialized RV
Multiple pathways

Success about 85% Recurrence about 30%

Ridge

Edward P. Walsh. Ebstein’s Anomaly of the Tricuspid Valve: A Natural Laboratory for Re-Entrant Tachycardias. JACC: Clinical Electrophysiology 2018;4(10):1271-1288, doi: 10.1016/j.jacep.2018.05.024

Careful EP study

Identify multiple accessory pathways
- Atrial pacing and extrastimuli
- Monitor precordial transition
Identify concealed pathways
Identify atriofascicular pathways

Multiple AP

Successful sites

Multiple AP

Multiple AP in AF

Complete characterization including retrograde conduction

Atriofascicular AP

True atriofascicular AP not uncommon
May participate as antegrade pathway in pathway-to-pathway tachycardia
May not always require ablation

Careful mapping

Guide for true annulus
Identification of atrial and ventricular electrograms

Identifying A and V

Unipolar EGM to identify

Confirm ablation of all APs - Parahisian pacing

Confirm ablation of all APs - Adenosine

Other Tips and tricks

Use a long sheath
Superior approach
3D mapping
ICE

Complications

Perforation
Coronary injury
Thromboembolism
AV block
Hemodynamic compromise

AV node displacement

Ho SY, Goltz D, McCarthy K, et alThe atrioventricular junctions in Ebstein malformationHeart 2000;83:444-449.

(A) The body of the atrioventricular (AV) node (within dotted line) is adjacent to the mouth of the coronary sinus in heart 3. (B) A more inferior section of the same heart shows the inferior nodal extensions (within white dots) at the level of the Thebesian valve. (C) This section from heart 5 shows the atrioventricular (AV) node at a level close to the mouth of the coronary sinus. The hinge of the septal leaflet is displaced from the atrioventricular junction. (D) This magnified view shows the extension (white star) of the conduction tissues from the atrioventricular node into the central fibrous body at the transition to the penetrating bundle. (E) This inferior section also from heart 5 is through the middle of the coronary sinus orifice. It is magnified in (F) to show the continuation of the nodal body at this level.

Coronary artery stenosis

Coronary Artery Stenosis After Radiofrequency Catheter Ablation of Accessory Atrioventricular Pathways in Children With Ebstein’s Malformation. Harald Bertram, Regina Bökenkamp, Matthias Peuster, Gerd Hausdorf, and Thomas Paul. Circulation Volume 103, Number 4. https://doi.org/10.1161/01.CIR.103.4.538

Thromboembolism

Interatrial communication very common
Use of long sheaths
Treat like left sided ablation

Summary - Challenges of APs in Ebstein's

Multiple AP
Anatomical abnormalities
Electrical abnormalities in atrialized RV
More prone to complications
Additional attention while mapping and ablating