**3.3 Ventricular arrhythmias**

Ventricular arrhythmias (VAs) can occur on both the normal and abnormal structural hearts. Structural heart diseases are most frequent, and it is well known that cardiomyopathies lead to cardiac injury, which is clinically expressed by VAs. In contrast to ischemic dilated cardiomyopathies (DCMs), the substrate for VAs in nonischemic DCM is not well defined, and patients may present with any type of VAs, including premature ventricular complexes, monomorphic or polymorphic ventricular tachycardia (VT), and ventricular fibrillation [4, 23, 24].

The two main strategies in the ablation of VTs are represented by the detection of the critical isthmus of the VT circuit and the modification of the arrhythmogenic substrate. However, considering the distribution of the scar in patients with DCM, endocardial mapping alone is often insufficient. Previous research demonstrated that combined endocardial and epicardial ablation improved the procedures results, and the mid-term outcomes in patients with previously failed endocardial only ablation and also as a first-line strategy [25, 26].
