Endocardium of RVOT as a source of triggers in BrS
The epicardial surface of the RV, particularly the RVOT, has been shown
to be the site of origin of phase-2-reentry-induced extrasystoles
capable of trigging VT/VF in the in ventricular wedge and whole heart
models of BrS.13-15,17-19 Consistent with these
experimental observations, numerous clinical
studies3-8,12,20 as well as experimental
studies21 have demonstrated that ablation of the RVOT
Epi substrate can significantly reduce the occurrence of VT/VF in the
setting of BrS. Ablation of the RVOT Endo has also been shown to reduce
BrS-associated VT/VF in some clinical cases.9-12 These
data suggest that RVOT Endo can be involved in the generation of VT/VF
in patients with BrS.
The present study points to the presence of an arrhythmogenic substrate
in the deep intra-trabecular structures of the Endo of the RVOT in the
setting of BrS, similar to that previously described in the Epi of the
RVOT.22 Consequently, ablation of either surface of
the RVOT has the potential to reduce BrS-related arrhythmogenicity.
When
applied to the ventricular endocardium, an ablation catheter is likely
to ablate both the “smooth” muscle and deep intra-trabecular
structures, thus exerting an ameliorative effect. An alternative
explanation for the effectiveness of Endo ablation in some patients is
that ablation of RVOT Endo may extend to the RVOT Epi, thus affecting
Epi BrS substrate (considering that the RVOT is relatively
thin).12,23
To the best of our knowledge, this is the first study to systematically
examine the AP characteristics of RVOT Endo in the setting of BrS using
intracellular microelectrode techniques. Our data suggest that the deep
structures of RVOT Endo, in addition to the RVOT
Epi,14,17 can be the source of the substrate for
development of phase 2 reentry, capable of triggering VT/VF in BrS.
Interestingly, there are substantial electroanatomical abnormalities on
the Endo RVOT surface in patients with Brugada syndrome detected with
unipolar mapping, and these abnormalities correlate with VF
occurrence.24