This is a multicenter, prospective, parallel, randomized controlled trial to test for non-inferiority with an ILAM-guided VT ablation compared to conventional voltage- based ablation. The study has two treatment arms: conventional voltage mapping and ablation (control arm). In the investigational arm, the ablation strategy is guided by ILAM to target deceleration zones, blinded to voltage mapping. In the control arm, ablation will be performed to extensively ablate all low voltage regions (<1.5mV) during sinus rhythm, right ventricular (RV) pacing, or left ventricular (LV) pacing, with discretionary use of pacemapping and activation mapping. In both arms, mapping with be performed with a multielectrode catheter (HD Grid) and ablation will be performed using an irrigated tip catheter (FlexAbility SE or Tactiflex catheters).

In the control armonly voltage mapping displays will be utilized (blinded to functional ILAM and fractionation). High density mapping with automated last deflection annotation (Ensite X) will be performed in all patients randomized to ILAM approach during either sinus rhythm or RV pacing.

Criteria

To participate in this clinical investigation, the subjects must meet all of the following inclusion criteria:

1. Patient is ≥18 years of age.

2. Able and willing to comply with all study requirements.

3. At least one documented episode of sustained MMVT (>30 sec) by either EGM or ECG (including Holter, or loop recorder) in the 6 months prior to enrollment.

4. Informed of the nature of the study, agreed to its provisions, and has provided written informed consent as approved by the Institutional Review Board/Ethics Committee (IRB/EC) of the respective clinical study site.

5. Refractory (i.e., not effective, not tolerated, or not desired) to at least one anti-arrhythmic medication (including, but not limited to beta blocker, mexiletine, amiodarone or sotalol) for treatment of MMVT.

6. Structural heart disease (ischemic or non-ischemic) with one of the following (a, b or c):

   1. Evidence of myocardial scar by echocardiography (segmental wall motion or wall thinning), CT (wall thinning) and/or MRI (presence of delayed enhancement /late gadolinium enhancement) . CT or MRI with scar is mandatory for inclusion of NICM., or
   2. Left ventricular ejection fraction (EF) <50% [documented within the last 6 months via transthoracic echocardiogram (TTE), MRI] with presence of scar, or
   3. Arrhythmogenic RV cardiomyopathy/dysplasia (per 2010 ARVC/D Task Force Criteria)

Exclusion Criteria

Subjects who meet any of the following exclusion criteria must be excluded from the clinical investigation:

1. Active infection (positive blood culture).
2. Patient is pregnant or nursing.
3. Cardiac surgery via sternotomy (CABG or valve repair/replacement) within 30 days prior to enrollment.
4. Contraindication to systemic anticoagulation (i.e., heparin, warfarin, or a direct thrombin inhibitor).
5. Currently receiving support via extracorporeal membrane oxygenation (ECMO) or ventricular assist device (VAD).
6. Left Ventriclar ejection fraction < 15%.
7. Stroke within 30 days or presence of LV thrombus within 1 month prior to enrollment.
8. Idiopathic VT or preprocedural imaging without scar (MRI or CT).
9. Limited life expectancy of 1 year or less.
10. Presence of mitral and aortic valves both mechanical.
11. Ventricular tachycardia secondary to electrolyte imbalance or any other reversible or non-cardiac cause.
12. Severe aortic stenosis or flail mitral valve with severed mitral regurgitation.
13. Thrombocytopenia (defined as platelet count <50,000/μl ) or coagulopathy.
14. Ventricular arrhythmias secondary to underlying channelopathies (LQTS, Brugada Syndrome).
15. Enrolled in an investigational study evaluating another device or drug that would confound the results of this study.
16. Other anatomic or co-morbid conditions that, in the investigator's opinion, could limit the patient's ability to participate in the study or to comply with follow up requirement of 1 year, or impact the scientific integrity of the study results.