Analysis of transient ST segment changes during ambulatory monitoring using the Karhunen-Loeave transform

The authors present an algorithm based on the Karhunen-Loeave transform (KLT) for robust automated detection of ischemic ST segment episodes and measurement of the duration of ischemia in two-channel ambulatory electrocardiographic data. The algorithm operates as a postprocessor to an existing arrhythmia detector. The episode detector incorporates a single-scan trajectory recognition technique in the KLT feature space. The algorithm differentiates between true ischemic ST segment changes and non-ischemic ST deviations caused by axis shifts. In evaluations using the European Society of Cardiology ST-T database, the algorithm achieved a gross ST episode sensitivity of 85.2%, with a positive predictivity of 86.2%. The gross ischemic ST duration sensitivity was 75.8%, with a positive predictivity of 78.0%.