Optimised Decrement Evoked Potential (DeEP) Mapping to Guide Ventricular Tachycardia (VT) Ablation in Patients With Structural Heart Disease VT

Inclusion Criteria: * ≥18 years old * Patients with cardiac implantable electronic devices (CIED) (e.g. pacemakers, cardiac resynchronisation therapy (CRT) devices, implantable cardioverter defibrillator (ICD) devices) * Eligible for VT ablation as part of standard care (urgent or elective) * Ischaemic heart disease and prior myocardial infarction (MI) (using the international definition of MI: Q waves or imaging evidence of regional myocardial akinesis/thinning in the absence of a non-ischemic cause with documentation of prior ischaemic injury) OR other structural heart disease (such as: arrhythmogenic cardiomyopathy (ACM), or dilated cardiomyopathy (DCM), or hypertrophic cardiomyopathy (HCM), or sarcoidosis, or myocarditis). * Catheter ablation of VT ablation using Abbott intracardiac mapping catheter and Ensite intracardiac mapping system. Exclusion Criteria: * Lacks capacity to provide informed consent * New York Heart Association (NYHA) class IV heart failure * Life expectancy of less than 12 months * Implanted with a ventricular assist device * Presence of mobile intracardiac thrombus * Reversible cause of VT * Women who are pregnant or nursing * Both mechanical aortic and mitral valves * Enrolment in a concurrent interventional clinical study that in the judgement of the investigator would increase risk to the patient or deem the patient inappropriate to participate in this study.