The aim of this study is to define the importance of non-invasive programmed stimulation (NIPS) in risk stratification of ventricular tachycardia (VT) recurrence after catheter ablation and to determine the optimal treatment strategy. The primary objective is to establish whether a new VT ablation based on NIPS inducibility will reduce the risk of VT recurrence compared to antiarrhythmic drug therapy.

The value of non-invasive programmed ventricular stimulation (NIPS) in the setting of ablation of ventricular tachycardia (VT) in patients with structural heart disease has been the object of studies in the last decade.

The technique is based on the feature, uniformly available in the Implantable Cardioverter-Defibrillator (ICD), to perform a complete programmed stimulation study from the apex of the right ventricle to assess the inducibility of ventricular tachycardia, similar to what is routinely performed during an invasive electrophysiology procedure. Data from our group indicate that 26% of patients who were non-inducible (apparent success) at the end of the ablation session become re-inducible to ventricular tachycardia at "late" NIPS (day 6). This finding, possibly related to partial recovery of conduction within the treated area, had prognostic significance, as it was associated with a 6-fold increased risk of VT recurrence at follow-up.

Recently Muser et al. reported similar findings (45/216 -21% of patients had clinical VT induced) with "late" NIPS performed on day 3. However, within this group of patients, the VT recurrence rate was significantly lower in those who had undergone, based on this finding, a re-do VT ablation as compared to those treated conservatively (rec in 1/11 of the Re-do ablation group, 9% vs. 24/34 in the conservative treatment group, 71%, p<0.01).

These data, however, originated from a retrospective observational analysis, where the indication of ablation was based on empirical physician preference.

No prospective randomized data compare the conservative attitude versus performing a new ablation in subjects who did not obtain a stable result after the first one. Therefore, this randomized multicenter clinical study aims to evaluate whether the repetition (Re-Do) of VT ablation process is superior to conservative medical therapy for reducing VT recurrences on post-procedural NIPS.

Inclusion Criteria:

• Patients with an implanted ICD (all brands)
• Patients who underwent a successful (non-inducibility of any VT) Ventricular Tachycardia Ablation procedure, the "index procedure", supported by EnSite Precision or CARTO 3D mapping systems for the following etiologies: previous MI, myocarditis, ARVD, IDCM.
• Induction of monomorphic VT at NIPS 3-7days after a successful index procedure
• Age 18 years or more
• Able to provide an informed consent to participate to the study and available to respect the assessments described in the protocol.

Exclusion Criteria:

• Inducible VT after index procedure
• Contraindication to anticoagulants
• Presence of thrombi
• Presence of Mitral and Aortic prosthetic valve
• Recent (<3 months) myocardial infarction or unstable angina or Coronary Artery Bypass
• Pregnant or nursing
• Ventricular Tachycardia caused by reversible pathology
• < 1 Year life expectancy according to the investigator