Table 3: Presence of Epicardial Substrate and Necessity of Epicardial Ablation According to Type of Cardiomyopathy.

Type of Cardiomyopathy	Epicardial Substrate	Epicardial Ablation	Comments
ARVC/D	Very frequent	First line or after ineffective endocardial ablation/arrhythmia recurrence	Histo-pathological studies show more extensive epicardial than endocardial scar tissue
Dilated cardiomyopathy	Frequent	After ineffective endocardial ablation/arrhythmia recurrence or may be considered first line in selected patients	No epicardial ablation necessary in cases with bundle-brunch-reentry or focal mechanism
Myocarditis	Probably frequent	May have a role, only scarce data	Inflammation involves mainly mid-wall and sub-epicardium
Chagasic cardiomyopathy	Very Frequent	May be attempted first line	Epicardial scar area larger than endocardial scar area
Hypertrophic cardiomyopathy	Probably frequent	May have a role, only small case series	Apical form of hypertrophic cardiomyopathy may more frequently have epicardial substrate
Brugada syndrome	Probably frequent	Very effective according to one single study	If frequent ventricular ectopics present endocardial ablation of ectopics very successful
Sarcoidosis	Probably frequent	May have a role, only small case series	Predilection of granulomas to the sub-epicardium
Ischemic cardiomyopathy	Less frequent	After ineffective endocardial ablation/arrhythmia recurrence	Epicardial ablation may be required more frequently in the presence of an inferior myocardial infarction
Idiopathic VT	Rare	Mapping and ablation mostly successful from within cardiac venous system in case of epicardial origin	Epicardial left VT origin likely if MDI ≥0.55 and VT origin remote from the sinus of Valsalva

ARVC/D = arrhythmogenic right ventricular cardiomyopathy/dysplasia; VT = ventricular tachycardia.