Dynamic Substrate Mapping (DSM) for Ischemic VT

Inclusion Criteria: * Have an ICD or CRT-D device * Had at least 3 documented device therapies to treat VT over last 3 months * Clinical VT is confirmed or suspected to be of ischemic origin * Scheduled for VT ablation procedure * LVEF \> or = 20% Exclusion Criteria: * Inadequate AAD washout (amiodarone should be maintained at current dose) * Unstable angina * Active ischemia * Cardiac surgery within prior 2 months * Evidence of infection * Prosthetic mitral or aortic valve or mitral/aortic valvular heart disease requiring surgical intervention * History of embolic event * Myocardial infarction within prior 6 weeks * Enrolled in another study * Recurrent sepsis or otherwise not a candidate for catheterization * Hypercoagulable state or inability to tolerate heparin therapy during procedure * Has had an atriotomy or ventriculotomy within prior 4 months * Life expectancy \< 6 months * Class IV NYHA classification