*2.3.1 Myocardial infarction related VT*

The previous study showed a good response with subendocardial resection to treat the subendocardial location of the VT substrate from surgical experience, which indicated the endocardial VT circuits [22]. Furthermore, the endocardial catheter ablation with mappable VT demonstrated good acute procedural success rate. However, the long-term outcome was unsatisfied [23]. A prior study examined all ischemic cardiomyopathy (ICM) VT cases with endocardial and/or epicardial mapping/ablation. Epicardial approach was applied in 14% of patients, and application of ablation in the epicardium was done in 8.5% patients. Part of the patient (0.5%) did not undergo epicardial ablation because of proximity to an epicardial coronary artery to the of identifying epicardial substrate [24]. In an Asian study from Taiwan, the epicardial approach for the ICM-related VT was rarely reported [14]. This may be related to the highest quality and convenience of Taiwan's public health system. A recent non-randomized study provided evidence of epicardial-endocardial approach in these patients [25]. Generally, the region of myocardial infarction does not appear to be predictive of epicardial involvement. On the other hand, imaging, such as cardiac magnetic resonance imaging (MRI), cardiac computed tomography, or nuclear scintigraphy suggesting transmural infarction may identify patients more likely to have epicardial substrate [26].

### *2.3.2 Idiopathic ventricular arrhythmia*

The recent review article summarized most common idiopathic VT arising from the right and left ventricle: (1) outflow tract VT, (2) fascicular VT, (3) intracavitary VT, (4) perivalvular VT, and (5) epicardial VT [27]. Around 1. 8–9. 2% of idiopathic VT were raised from the epicardium. In the prior study, the electrocardiography is a useful parameter for predicting the successful ablation sites of VT originating from the continuum between the aortic sinus of Valsalva (ASV) and the left ventricle (LV) summit [28]. In the results, aVL/aVR Q-wave ratio is useful in the prediction of successful ablation sites. A coronary venous approach / pericardial access might be required with a cutoff value of 1.536-1.740 and > 1.740 respectively.

#### **2.4 Epicardial approaches were more favorable than endocardial approach**

#### *2.4.1 Brugada syndrome catheter ablation*

Brugada syndrome (BrS) is one of the main causes of sudden cardiac arrest in young population [29]. The efficacy and adverse effects of anti-arrhythmic drugs on BrS was disappointing. Catheter ablation emerged and offers an alternative therapeutic strategy for these patients with repeat recurrent implantable cardioverter defibrillator (ICD) shock after the ICD implantation. Nademanee et al. first demonstrated the effectiveness and safety of ablating the arrhythmogenic electrogram at the epicardium of right ventricular outflow tract (RVOT) to decrease the VT/ VF burden [30]. Further study on the post-mortem heart demonstrated interstitial fibrosis and reduced gap junction expression in the epicardium of RVOT in BrS patients. The abnormal fibrosis resulted in arrhythmogenic potentials. Eliminating the arrhythmogenic potentials by using ablation could abolish the BrS ECG pattern and reduce VT/VF burden. In the clinical practice, the operator may perform

*Epicardial Radiofrequency Ablation: Who, When, and How? DOI: http://dx.doi.org/10.5772/intechopen.99824*

#### **Figure 3.**

*Local fractioned potential in the epicardial right ventricular outflow tract of a patient with Brugada syndrome. The left panel demonstrated local abnormal signal and delayed electrogram, which was localized in the epicardial right ventricular outflow tract. (red arrow, right panel) this patient was diagnosed as Brugada syndrome and survived from an episode of sudden cardiac death due to ventricular fibrillation.*

epicardial mapping and identified the slow conduction zone and abnormal electrogram in the RV epicardially. (**Figure 3**) The electrophysiological group in Taipei Veterans General Hospital first introduced the warm water instillation, which would enhance the phenotype and functional substrate in the patient with BrS. Ablation by targeting the triggers and abnormal epicardial substrates provided an effective strategy for preventing ventricular tachyarrhythmia recurrences in BrS [31].

#### *2.4.2 Arrhythmogenic right ventricular cardiomyopathy*

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a heritable desmosome disorder. The clinical manifestations vary from asymptomatic concealed stage, electrical abnormality with ventricular arrhythmias (VAs), to progressive heart failure [32, 33]. Catheter ablation is emerging as an alternative therapy for drugrefractory VAs in patients with ARVC. Although the catheter ablation could result in acute procedural success with VT termination, the high incidence of recurrence limited the role of ablation in ARVC initially [34, 35]. The application of epicardial and endocardial ablation of VT in the patients with ARVC had been proposed with good effects acute and long-term outcome and VAs-freedom [36, 37]. Recent studies also demonstrated that 45 ~ 84. 6% patients were free from VA recurrences or ICD therapy through the combination of endocardial and epicardial ablation [38, 39]. Epicardial approach is required in more than one third ARVC patients for achieving non-inducibility in the prior reports [40]. The number of fulfilled SAECG criteria was correlated to the extent of diseased epicardial substrate and could be a potential surrogate marker to predict the requirement of epicardial ablation in ARVC with drug-refractory VA [40].

#### *2.4.3 Non-ischemic cardiomyopathy*

In contrast to ischemic cardiomyopathy, non-ischemic cardiomyopathy (NICM) consists of a heterogeneous group of diseases [41] affecting the myocardium. Despite the progress and improvement in the pharmacological medication of heart failure in recent decades have significantly decreased the disease progression and mortality in NICM patients, anti-arrhythmic medications and ICD implantations remain the most important treatment for patients carrying a high risk of VT/VF or who have experienced aborted SCD due to fatal VT/VF [42]. Owing to the improvement in electro-anatomic mapping and ablation catheter, catheter ablation of VT in NICM patients has been recognized as an upcoming issue [43]. A prior study proven the promising results that a successful catheter ablation could reduce VT recurrences and improve the survival in NICM patients regardless of the functional class status or left ventricular function [44]. NICM VTs in different disease entities could result from non-uniform arrhythmogenic substrates, which can lead to different ablation outcomes.

With the exception of ARVC and BrS, the arrhythmogenic substrates in NICM that could be identified by electroanatomic mapping, are mostly located in the base or perivalvular region of the LV, which is distinct from the substrate ICM [45]. The arrhythmogenic potentials could be identified from the endocardial/epicardial aspect in the patients with NICM [46]. These arrhythmogenic substrates frequently associate fibrosis tissue that leads to conduction disturbance and fractionated electrograms [47]. Aside from the electroanatomic substrate mapping with bipolar/unipolar voltage, cardiac MR can provide additional information to unmask the scar distribution as a non-invasive manner [48–50]. Additionally, patients with scar involving the inferolateral aspect of the LV, which frequently requires an epicardial approach, usually have a better prognosis than those with anteroseptal scar [51].

A comprehensive investigation of patients with NICM and VT includes cardiac imaging and genetic testing. These information might enable recognition of undiagnosed diseases, such as isolated and active cardiac sarcoidosis or inherited cardiomyopathies. An accurate diagnosis could improve patient selection for ablation and early consideration of individualized treatments [52].

### **3. When should be considered to perform the epicardial approach?**

An epicardial approach could performed for patients with refractory ablation from an endocardial approach. The clinical documentation of surface ECG could provide specific electrocardiographies evidence supporting an epicardial origin [28, 53, 54]. In cases with a disease entity favoring an epicardial substrate, or those with electroanatomic mapping supporting the existence of a diseased epicardial substrate, an epicardial approach could be considered [30, 55, 56].

Before preparing for epicardial approach, the first step is to localize the VT origin and identify the potential regions of arrhythmogenic substrates. The surface ECG morphologies provide the information about the origin and the potential need for an epicardial approach [53]. Standardized echocardiography or intracardiac could delineate the valvular structure, area of hypokinesia or akinesia, and excluding any intracardiac thrombus [57]. Computed tomography (CT) and cardiac MRI with a late gadolinium enhancement, could localize the regions of abnormal tissue in specific protocol [48–50]. The distribution and extent of the scar is useful for deciding the ablation strategy, such as an epicardial approach, transcoronary venous ablation,

**Figure 4.**

*Cardiac magnetic resonance imaging (CMRI) and three-dimensional reconstruction in a patient with nonischemic myocardial infarction. The CMRI demonstrated a late gadolinium enhancement (LGE) in the mid posterior wall. The three-dimensional reconstruction was performed to guide the catheter ablation.*

alcohol ablation, or simultaneous bipolar ablation. The integration of the reconstructed images obtained from CT and MRI and 3-D navigation, mapping systems (**Figure 4**) can aid in the illustration of the structural complexity and avoidance of damage to the critical regions, in terms of vascular or nervous structures.
