Disclosed herein are methods, systems, and devices for identifying increased likelihood of non-ST elevation myocardial infarction (NSTEMI) in a patient based on ECG data. The methods can include determining based on the ECG data that the patient lacks ST elevation (STE) and that the patient exhibits a ventricular repolarization dispersion (VRD) score that exceeds a predetermined threshold value. The VRD score can be based in part on a T wave complexity ratio that serves as a temporal marker of VRD for the patient. Other markers of spatial and time qualities of repolarization can also be included in the VRD score. An elevated VRD score in the absence of STE can indicate a likelihood of NSTEMI in the patient and a potential major adverse cardiac event.