Ebstein's Anomaly of the Tricuspid Valve: A Natural Laboratory for Re-Entrant Tachycardias.

Ebstein's anomaly of the tricuspid valve is a relatively rare form of congenital heart disease that has long been a challenge to electrophysiologists and cardiac surgeons. In addition to the hemodynamic burden of the actual valve defect, Ebstein's patients must also contend with an extraordinarily high incidence of tachyarrhythmias, most of which can be attributed to accessory atrioventricular pathways (APs) located along the posterior and septal border of the tricuspid valve where the valve leaflets are most abnormal. It is the only congenital heart defect with such a dramatic predisposition toward APs. Although it is logical to postulate a link between the anatomic deformity and the conduction abnormality, the exact nature of this link is still not fully understood and remains a fertile area for investigation that might shed light on abnormal conduction pathways in many other forms of heart disease. Furthermore, for reasons that are only now being fully appreciated, successful catheter ablation of APs in this setting is frequently more challenging than would be expected in a structurally normal heart. This review will explore the gross and microscopic anatomy of Ebstein's anomaly with attention to features that could be important to both arrhythmogenesis and ablation therapy in this unique population.