**6. Correlation between functional and ultrastructural substrate**

fractionated late potentials in the anterior zone of epicardium of RVOT normalized the ECG BrS pattern and prevented VT/VF in all but one patient during a follow-up of 20 ± 6 months [17]. Recently, Brugada et al. in 14 inducible patients reported abnormal EGMs only in epicardium of the anterior free wall of right ventricle and in RVOT. RFA eliminated both ECG

In our study, the endocardial RFA in 13 patients resulted in normalization of the ECG BrS pattern, disappearance of end-QRS notching or slurring and suppression of inducibility in all patients during a mean follow-up of 47.7 ± 15.5 months (**Table 1**) [19]. About 30 days after RFA a flecainide testing did not develop ECG BrS pattern. Seven patients who entered to procedure with spontaneous type 1 ECG pattern showed ECG normalization at the end of the procedure. Immediately after RFA was applied, activity and varying degrees of changes in ST segment were observed. With following applications of RFA the ECG pattern progressively decreased (**Figure 7**). After RFA local abnormal diastolic EGMs completely disappear and systolic EGMs were replaced by residual very low voltage areas. The mean time of procedure and fluoroscopy were 112 ± 24.5 and 13.7 ± 5.5 minutes, respectively (Table I). Postprocedure, predischarge, and follow-up 12-lead ECG confirmed the absence of BrS ECG pattern (**Figure 6C**). The patients were asymptomatic and free of arrhythmic events in the 24-hour ambulatory ECG monitoring and in follow-up the ICD interrogation. Two patients (15%) had a near-syncope with prodrome at 24 of 46 months and at 18 of 36 months of

Sunsaneewitayakul et al. reported that endocardial RFA on the late depolarization zones modified the ECG BrS pattern in three patients and suppress the VF storm in four patients, during follow-up of 12–30 months [16]. Similarly, we obtained suppression of inducibility, normalization of BrS ECG pattern and early repolarization pattern with endocardial RFA of

**Figure 7. Effects of radiofrequency ablation on ECG.** In the N°3 patient during endocardial RFA, intense activity and varying degrees of ST segment changes are shown. The ECG pattern progressively decreases with the following applications (red arrows). After RFA the local abnormal diastolic EGMs completely disappeared and systolic EGMs were

BrS pattern and inducibility, with a median follow-up of 5 months [18].

134 Cardiac Arrhythmias

follow-up respectively, without arrhythmias in ICD interrogation.

replaced by residual low voltage areas [19].

Coronel et al. show in a heart explanted of a BrS patient, fibrosis with epicardial fat infiltration as well as conduction slow without transmural repolarization differences [35]. Furthermore, interstitial fibrosis, fat tissue and myocyte disorganization with reduced gap junction expression in the presence of fractionated and unfractionated low voltage systolic EGMs in the endocardium and epicardium of RVOT was reported with optical microscopy [36–38].

In two patients, before RFA and after right internal jugular venous access through a steerable sheath we advanced a bioptome to RVOT and connected to 3-dimensional (3D) mapping system [19]. Guiding by electroanatomic and voltage map two samples of endo-myocardial biopsies of the three previously defined zones of substrate was obtained. Samples were fixed in 4% glutaraldehyde and 0.1% sodium phosphate (pH 7.4) for transmission electron microscopy (TEM) study as was described previously [39]. As show **Figure 8** the ultrastructural substrate and functional substrate were correlated [19]. In the **Figure 8A**, the patient N°13 in (a), (d) and (g) shows electro-anatomic and voltage map (functional substrate) with a central area of substrate of 25 mm2 located in the intermediate-anterior zone of the RVOT and the bioptome

**Figure 8.** Correlation between functional and ultrastructural substrate. On the left side the electro-anatomic and voltage map (functional substrate) and bioptome connected to the navigation system is shown. On the right side the ultrastructural substrate is shown. Scale Barr: 3.33, 2.2 and 1.42 μm; mitochondria (mi); myofibrils (mf); Purkinje cell (pc); myofibrillar rests (\*); lipofusin deposit (ld); intercalated disk (id); remains of erythrocytes (er) [19].

connected to the navigation system. In (b) and (c) on the right side can be seen the ultrastructural substrate which corresponds to normal zone with mitochondria, myofibrils, and a Purkinje cell of normal characteristics. In contrast, in the peripheral zone of substrate (e and f) note that when approaching to pathological area, cytoplasmic vacuolization, myofibrillar and mitochondrial disorganization with myofibrillar residue can be observed. The (h) and (i) corresponds to the central zone, which depicts strong vacuolization and cell destruction with intense cytoplasmic disorganization and myofibrillar residue. In the **Figure 8B**, the patient N° 11 in (a), (d) and (g) shows the voltage and electro-anatomic map (functional substrate) with central area of substrate of 8mm2 located in the top-septal zone of the RVOT. In (b) and (c) on the right side can be seen the ultrastructural substrate which corresponds to normal zone with normal characteristics of mitochondria, myofibrils, and a Purkinje cell. The approaching to pathological area in the peripheral zone of substrate (e and f), myofibrillar disorganization, citoplasmic vacuolization, swelling and disappearance of mitochondrial crests, myofibrillar rests and remains of erythrocytes were observed. The (h) and (i) corresponds to the central zone showing strong vacuolization and cell destruction and myofibrillar residue. Fat replacement, lymphocytic infiltration, Chagasic myocarditis, collagen tissue or apoptotic bodies were not observed.

In addition, we found pre-systolic potentials as was previously reported by Haissaguerre et al. [15]. As show **Figure 8**, the Purkinje fibers in RVOT could be involved in the origin of pre-systolic potentials and in genesis of early-onset PVCs that can trigger VT or VF, by spon-

Endocardial Approach for Substrate Ablation in Brugada Syndrome

http://dx.doi.org/10.5772/intechopen.75932

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In patients with BrS of high risk the substrate RFA may be a potential option of treatment. We successfully ablated the substrate of BrS from the endocardium based on the electrophysiological and ultrastructural findings. Our data together with the observations of other researchers suggest a transmural substrate, contributing to future definition of the arrhythmogenic substrate in BrS. As many phenotypes are involved in BrS, it is not unthinkable that different substrates may exist in BrS. ECG analysis during administration of a sodium channel blocker allows approximately determined the size and location of substrate. Careful endocardial mapping allows identify late potentials, presystolic and diastolic EGMs as a new risk marker to guide an endocardial substrate RFA, probably with the same results what a more complex epicardial ablation. A comparative study between endocardial and epicardial RFA should be performed.

This research was supported by funding sources from the Electrophysiology Division (Model Heart Center) to PET, and PIP 2015 No.183 (CONICET Argentina) and PICT 2013 No. 1949 (ANPCyT, Argentina) grants to SSS and SMH. We thank to Abbott-Argentina for providing

taneous depolarization or micro-reentry circuit in the Purkinje network [30].

**8. Conclusion**

**Acknowledgements**

**Conflict of interest**

**Abbreviations**

financial support to publication.

AP action potential BrS Brugada syndrome ECG electrocardiogram

EGMs electrograms

f-QRS fragmented QRS

EPS electrophysiology study

The authors declare none conflict of interest.

It is important to note that when we approach to pathological areas progressive cell damage was observed. In the central zone of substrate low voltage systolic EGMs coincided with strong cell destruction and cytoplasmic disorganization. The peripheral zone of substrate with cell damage, mitochondrial swelling and myofibrillar residue without apoptotic bodies coincided with late potentials, diastolic and/or presystolic activity (**Figures 2** and **3**). These findings support mitochondrial energy loss as possible non-apoptotic progressive tissue damage and death cell. Our results suggest the interesting possibility that substrate could be generated by an abnormal expression of neural crest cells localized in RVOT during cardiac development. Because an epicardial and endocardial substrate was demonstrated, our findings together with those of other researchers support the probability of a transmural substrate.
