High-risk accessory pathway associated with a rare right atrial diverticulum: a case report.

Background: Right atrial (RA) diverticulum is a rare malformation that can, in some cases, harbour an accessory pathway (AP). This report describes the case of a patient with RA diverticulum associated with a high-risk right posteroseptal AP. Successful radiofrequency catheter ablation was performed, eliminating the AP and resolving the patient's pre-excitation. Case summary: A 33-year-old man with a 15-years history of an AP presented with two isolated, self-limited episodes of palpitations. A 12-lead ECG during normal sinus rhythm showed pre-excitation consistent with a right posteroseptal AP. The electrophysiological study identified an inducible antidromic atrioventricular tachycardia (tachycardia cycle length = 220 ms) due to a high-risk AP with robust conduction in both antegrade and retrograde directions. The AP was localized inside a RA diverticulum near the tricuspid annulus, confirmed through angiography and 3D high-density mapping. Radiofrequency ablation was successfully performed at the top of the diverticulum at a site recording an AP potential. To further characterize the diverticulum, a cardiac magnetic resonance was performed, and showed a maximum dimension of 20 × 16 mm. Since the diverticulum did not cause any haemodynamic impact, surgical intervention was deemed unnecessary. Discussion: 'Anatomical' APs are rare, often described in the literature as diverticula of the coronary sinus. However, RA diverticula associated with APs are exceedingly uncommon, with only a few cases reported. This case underscores the importance of considering structural abnormalities like RA diverticula in patients presenting with unusual arrhythmic patterns and highlights the effectiveness of radiofrequency ablation as a definitive treatment in such complex scenarios.