Discussion

Posteroseptal accessory pathways are the second most common accessory pathways, and their ablation is associated with longer procedure times, greater fluoroscopic exposure, and more radiofrequency lesions than in any other location. Posteroseptal accessory pathway ablation can sometimes be challenging due to the complex anatomy of this region, the possible requirement of right-/left-sided mapping, epicardial connections involving the coronary venous system and diverticulum, and the risk of injury to the coronary artery. ^{Reference Jackman, Wang and Friday3}

Coronary sinus anomalies are rare but seem to be a significant cause of failure in the case of the ablation of posteroseptal pathways. If such anomalies are suspected, coronary sinus angiography should be performed during the ablation procedure. The detection of coronary sinus structures by angiography can assist in the elucidation of the anatomical cause of arrhythmogenic substrates and guide catheter manipulation in searching for the target site of radiofrequency application. ^{Reference Weiss4,Reference Wissner, Ouyang and Kuck5}

The coronary sinus has a myocardial coat with sleeve-like extensions. The extensions of this coat can connect to the ventricular epicardium through the posterior cardiac vein, middle cardiac vein, or a diverticulum neck and form the epicardial posteroseptal and left posterior accessory pathway. ^{Reference Sun, Arruda, Nakagama, Lazzara and Jackman6,Reference Von Ludinghausen, Ohmachi and Boot7} Previous studies indicate that in the presence of a coronary sinus diverticulum, the accessory pathway is likely to be in the diverticulum. However, there are also reports in which accessory pathways have been successfully ablated at sites different from the diverticulum in adult patients diagnosed with a coronary sinus diverticulum. Weiss et al ^{Reference Weiss4} presented a series of nine patients with the coronary sinus diverticulum who underwent successful ablation. The accessory pathway was located within the neck of the diverticulum in seven of these patients, and on the atrial side of the posteroseptal tricuspid annulus in the remaining two. Sun et al ^{Reference Sun, Arruda, Nakagama, Lazzara and Jackman6} showed the presence of a coronary sinus diverticulum in 36 patients (7.5%) in a large series of 480 patients with posteroseptal or left posterior accessory pathways. In two of these patients, the accessory pathway was associated with two different anatomical structures other than the diverticulum (posterior cardiac vein and the collateral vein between the middle cardiac vein and posterior cardiac vein). These studies suggest that in the presence of a coronary sinus diverticulum, the accessory pathway is rarely found elsewhere ^(4,6). In our case, the accessory pathway was found in the middle cardiac vein, although the patient had a coronary sinus diverticulum. This may be due to the coronary sinus myocardial coat, which has the potential to form an accessory pathway and covers the terminal part of the middle cardiac vein, as described by Sun et al. ^{Reference Wissner, Ouyang and Kuck5}

In conclusion, to our knowledge, this is the first report on a children with a coronary sinus diverticulum and Wolff-Parkinson-White syndrome who underwent successful epicardial accessory pathway ablation through a site other than the coronary sinus diverticulum. In the case of endocardial radiofrequency ablation failure, the posteroseptal pathway should be kept in mind, and coronary sinus angiography should be performed. In the presence of a coronary sinus diverticulum on angiography, the accessory pathway will likely be in that location. However, in cases with a coronary sinus diverticulum where ablation is not successful, as in our patient, other coronary sinus structures, for example, the middle cardiac vein should be considered as potential accessory pathways.