a processor including:

a cardiac signal vector module configured to measure, from an electrical cardiac signal, a first dominant vector corresponding to a direction and magnitude of maximum signal power of an ST-T first segment of at least one cardiac cycle of a subject and at least a second dominant vector corresponding to a direction and magnitude of maximum signal power of a P-QRS second segment of the cardiac cycle, wherein the P-QRS segment includes the P-wave and extends to and includes the S-wave; and

an ischemia detection module configured to measure a change in the first dominant vector and the second dominant vector, to form a difference by subtracting a measured change in the second dominant vector from the measured change in the first dominant vector, and to declare whether an ischemic event occurred using the difference.