A technique is provided for detecting episodes of cardiac ischemia based
on an examination of post-T-wave signal segments. Since cardiac ischemia
is often a precursor to acute myocardial infarction (AMI) or ventricular
fibrillation (VF), the technique thereby provides a method for predicting
the possible onset of AMI or VF so that a warning may be delivered to the
patient. The warning preferably includes both a perceptible electrical
notification signal applied directly to subcutaneous tissue and a warning
signal delivered via short range telemetry to a handheld warning device
external to the patient. In one example, the onset of cardiac ischemia is
identified by detecting a sharp falling edge within post-T-wave signals
by filtering the signals using a high-pass filter having a cutoff
frequency of at least 1 Hz. The total amount of energy in the filtered
signal is calculated and compared against various thresholds.