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.