The most common tool used for cardiac diagnosis is based on electrocardiogram (ECG) measurement and interpretation. Traditional ECG includes information about the timing of cardiac electrical events and the time intervals between two or more such events. For example, transmural repolarization, reflected by the T wave in an ECG, can indicate a plurality of abnormalities that mark susceptibility to life-threatening arrhythmias. Such abnormalities can be associated with genetic defects, various acquired cardiac dysfunctions, electrolyte disorders, and certain prescription and non-prescription drugs.