DISCUSSION
Although various ablative strategies have been designed over the last years, the success rate of catheter ablation in patients with LSPAF remains low, with wide variations in ablation techniques among operators. Increasing evidence suggests that the hybrid approach could represent a more aggressive, but greatly effective treatment for such patients(10).
The current report is the first study to date describing the adjunctive role of BB ablation in patients with LSPAF refractory to medical therapy. It resulted in the following important findings: (A) Bachmann’s bundle ablation in the setting of a two-staged hybrid ablation is safe and highly effective with 96% of patients being arrhythmia-free at 12-months, off AADs and without a need for re-ablation. (B) Adding this surgical ablation target, where the BB is supposed to be anatomically located, was easy to perform without significant increase in procedural time and did not require further blunt dissection. (C) BB ablation does not increase the risk of periprocedural complications.
The 12-month success rate observed in the CONV group is consistent with prior reports. Muneretto et al. reported an 88% success rate at 1 year and in the past the same group described a 90% success rate with a sequential-staged approach(4, 11). Kress et al. achieved an AF-free survival of 72% at median follow-up of 16 months(12). Other authors(13, 14) achieved sinus rhythm in over 80% of the patients and resulted in substantial left atrial and left ventricular reverse remodeling, improvement in the ejection fraction, functional status, and even a decrease in the NT-pro BNP serum levels after twelve months.
It is noteworthy that adjunctive BB ablation resulted in 96% of the patients being arrhythmia-free, off AADs and without a need for re-ablation. Bachman’s bundle may be involved in a number of unstable re-entrant circuits and it has been hypothesized that an effective lesion of the BB would prevent induction and maintenance of AF. Structural changes of BB may cause longitudinal dissociation of adjacent muscle fibers, facilitating re-entry and hence the development of AF(6). In addition, BB ablation implies a greater amount of ablated tissue reducing the critical mass necessary to sustain AF and may eliminate “driver tachycardias” and arrhythmogenic foci outside the pulmonary veins.
Notably, no complications were specifically attributable to the adjunctive BB ablation. We found a significant difference between the two groups in spontaneous conversion to sinus rhythm during the staged endocardial ablation and in terms of subsequent arrhythmia inducibility. In the BB group, all patients converted to sinus rhythm during the endocardial ablation and none needed cardioversion. This represents a major finding if we consider that only 5 patients in the conventional group converted to sinus rhythm during the ablation while 13 patients needed electrical cardioversion. Differences in inducibility rate between groups were even more impressive, especially considering the aggressive protocol of induction used in our study: only one patient remained inducible in the BB group compared to 19/30 patients in the conventional groups. These observations suggest that BB plays a major role in the perpetuation of atrial fibrillation and should prompt to include the ablation of BB in the ablation schemes used for LSPAF.
In 7 patients of the CONV group, mitral isthmus line was not successfully completed after catheter ablation. One of them had AF recurrence, however, this number was too small for any meaningful conclusion. Leftward extensions of the BB bifurcate to pass to either side of the left atrial appendages: it is our opinion that BB ablation could have facilitated in some way the mitral isthmus block obtained in all patients of the BB group.