Introduction and objectives: The development of ablation techniques for supraventricular arrhythmias in patients with Ebstein's anomaly have led to a need for better understanding of the morphology of the triangle of Koch and the position of the atrioventricular (AV) node in this structure.
Methods: The study involved 17 human hearts: 11 with Ebstein's anomaly (age range: 37 weeks' gestation to 1 week after birth) and 6 structurally normal hearts (age range: 35 weeks' gestation to 2 days after birth). The area of the triangle of Koch was calculated and the length of the AV node and the bundle of His were measured.
Results: The area of the triangle of Koch was significantly smaller in specimens with Ebstein's anomaly than in control specimens (17.5+/-4.5 mm2 vs. 25.5+/-6.5 mm2; P< .05). The length of the AV node and its extensions were similar in hearts with Ebstein's anomaly and normal hearts. The AV node was displaced towards the base of the triangle in 73% of specimens with Ebstein's anomaly, and the inferior extensions reached the level of the cavotricuspid isthmus. In 91% of specimens with Ebstein's anomaly, the entry of the His bundle occurred before the apex of the triangle was reached and its length was shorter.
Conclusions: Morphologic findings in this study indicate that performing an ablation procedure close to the base of the triangle of Koch in patients with Ebstein's anomaly could result in AV nodal block.