Examining the causes of ablation failure in the Wolff-Parkinson-White syndrome

This editorial refers to ‘Wolff–Parkinson–White ablation after a prior failure: a 7-year multicentre experience’ by F. Sacher et al ., on page 835. It is estimated that Wolff–Parkinson–White (WPW) syndrome affects 1–3/1000 persons. Albeit low in prevalence, sudden cardiac death may occur in the setting of atrial fibrillation, caused by rapid anterograde conduction over an accessory pathway and resulting in ventricular fibrillation. A new era in curative treatment was initiated when radiofrequency (RF) current catheter ablation became available in the early 1990s. 1 , 2 According to international guidelines, catheter ablation is a class I indication for patients presenting with WPW syndrome. Accessory pathway ablation using RF energy is supported by a high success rate of 95% combined with a low recurrence rate of 5%. 1–4 In 1996, Morady et al . 5 examined the potential causes of ablation failure in WPW syndrome. Since then, interventional cardiac electrophysiology has seen a remarkable transformation. The increasing number of patients undergoing atrial fibrillation ablation has lead to an acquired comfort in transseptal puncture, whereas alternative power sources such as cryo-energy are more commonly used in the electrophysiology laboratory. Concurrently, these laboratories have witnessed a decline in the total number of patients referred for accessory pathway ablation, posing a disadvantage for trainees in the field of electrophysiology and less experienced operators. As a result, one may speculate on the impact of these changes on the outcome of accessory pathway ablation. Sacher et al . 6 provide an updated multicentre data survey on the result of accessory pathway ablation in patients with prior failure referred to three tertiary medical centres over a period of 7 years. The authors emphasize the most common pitfalls to successful ablation according to accessory pathway location and provide insightful solutions to overcome these difficulties. Essentially, the causes of ablation failure may be divided into three entities: difficult or unexpected anatomic pathway location, technical issues, and operator-dependent. Catheter ablation may prove difficult if the accessory pathway is in close proximity to the His-bundle at a midseptal or anteroseptal location, increasing the risk of inadvertent complete atrioventricular block. The use of a long sheath may facilitate catheter stability if the accessory pathway is located along the right midseptal or anteroseptal region. In these cases, we favour advancement of the ablation catheter from the right jugular vein, since this site of access is in direct alignment with the location of the accessory pathway. Stable wall contact is accomplished by counterclockwise torque of the catheter. In addition, we found that an anteroseptal pathway may be successfully ablated from the non-coronary cusp. 7 Some operators prefer to use cryothermia. Our laboratory routinely uses RF current when ablating para-Hisian pathways. A His potential is practically always recorded at the earliest site of accessory pathway activation. However, the His bundle is protected by fibrous tissue, whereas the accessory pathway is superficially located, making damage to the His bundle very unlikely with the judicious use of RF energy. An epicardial accessory pathway location may not be amenable to a routine endocardial approach. If a posteroseptal accessory pathway is suspected, coronary sinus angiography will facilitate proper anatomic delineation and catheter ablation. In 21% of patients with a suspected posteroseptal or left posterior accessory pathway, coronary sinus angiography demonstrated a diverticulum originating from the middle cardiac vein, coronary sinus, or both. 8 Ablation is performed by advancing the ablation catheter into the coronary sinus, targeting the neck of the diverticulum. In rare cases, an epicardial accessory pathway may mimic electrocardiographic criteria of a manifest right anteroseptal accessory pathway. Clues to the correct diagnosis during endocardial mapping are: (i) the earliest local ventricular potential fails to precede the surface delta wave and (ii) lack of accessory pathway potential recording at the region of the His bundle. Epicardial mapping within the anterior portion of the great cardiac vein will demonstrate an accessory pathway potential and ablation at this location will result in block of the accessory pathway. 9 Proper choice of vascular access is a crucial determinant of a successful ablation outcome. Lesh et al . 10 compared a transseptal and retrograde approach for ablation of left accessory pathways and found that both techniques complement each other providing nearly 100% success if used in combination. Owing to the need for intraprocedural anticoagulation, a transseptal approach should be attempted first. Energy settings should be adjusted to the mode of access. Lower power is used if ablation is performed from below the mitral valve annulus where stable catheter contact is easily established. In contrast, higher power settings are required if ablation is performed from the atrial aspect via a transseptal approach. Furthermore, accessory pathways may not always be amenable to conventional RF catheter ablation, necessitating the use of an irrigated tip catheter in order to achieve sufficient power delivery. Finally, procedural failure may simply be explained by the operator's lack of experience, resulting in misinterpretation of surface or intracardiac electrograms and the inability to identify the ideal ablation site. A prerequisite for successful ablation is careful mapping and recording of an accessory pathway potential; an advanced skill that takes time and precision. Continued education in accurate interpretation of intracardiac electrograms and recognition of subtle changes in the surface electrocardiogram as well as more frequent exposure to patients with WPW syndrome should allow for advancement beyond these limitations. Ultimately, accessory pathway ablation for the treatment of WPW syndrome should not evolve into a lost art amidst rather complex procedures such as ablation of atrial fibrillation. Conflict of interest: none declared.