Radiosurgery for the Treatment of Refractory Ventricular Extrasystoles and Tachycardias

Inclusion Criteria: * Patients with structural heart disease and implantable cardioverter defibrillator (ICD) * Age \> 18 years * either 1. Recurring symptomatic monomorphic ventricular tachycardia that requires ICD intervention (e.g. shock or anti-tachycardia stimulation). At least 3 episodes within the 3 months prior to inclusion or 2. induction of symptomatic monomorphic ventricular tachycardia that requires ICD intervention (e.g. shock or anti-tachycardia stimulation). Induction triggered by ICD or during electrophysiology studies (EPS) or both, a) and b) * Refractory to antiarrhythmic combination therapy * Beside the cardiac conditions: No competing illness that would additionally limit the life expectancy to less than 6 months * No prior radiation therapy in the thorax area * No pregnancy and no active breastfeeding * Ability to consent and consent to study participation Exclusion Criteria: * ICD electrode malfunction of ICD readings outside reference range * Lack of evidence of a myocardial scar (Computer tomography or magnetic resonance tomography for MRI-capable ICD aggregates or electrophysiological measurement) * No possible induction of symptomatic monomorphic ventricular tachycardia non-persistent or persistent with delivery of ICD therapies such as antitachycardic pacing or shock * Contraindication to radiosurgery (e.g. precise target volume definition not possible due to image artifacts created from a left ventricular assist device (LVAD)) * Inability to consent or missing or withdrawn consent