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