Abstract: Described herein are implantable systems, and methods for use therewith, to predict whether ventricular tachycardia (VT) or ventricular fibrillation (VF) is imminent, estimate ischemic burden and/or characterize an electrical substrate of the LV chamber. For each of a plurality of cardiac cycles, a pacing vector comprising a first set of electrodes is used to deliver a pre-pacing pulse at a site within the LV chamber (wherein the pre-pacing pulse is delivered prior to an intrinsic activation of the LV chamber), and a sensing vector comprising a second set of electrodes is used to detect an evoked response to the pre-pacing pulse. The detected evoked responses to the pre-pacing pulses are analyzed, and results of the analysis are used predict whether VT or VF is imminent, estimate ischemic burden and/or characterize an electrical substrate of the LV chamber.