KARHUNEN-LOEVE TRANSFORM AS A TOOL TO ANALYZE THE ST-SEGMENT - COMPARISON WITH QT INTERVAL

The spatial and temporal courses of ventricular repolarization are qui te sensitive to the biochemical and biophysiologic environment of the myocardial cells, and are therefore often an early marker of heart dis ease, particularly of ischemia. The detailed morphology of the surface electrocardiogram contains considerable information about the repolar ization process. The ST-segment changes with ischemia, injury, and dru gs. The QT interval is affected by drugs, heart rate, and autonomic to ne, and in some situations may identify individuals at high risk for a rrhythmias and sudden death. Variability in the shape, including durat ion, of the ST-T waves reflects autonomic nervous system activity and may identify high-risk patients. Automated methods for quantitatively characterizing ST-T complexes are important in studying long-term elec trocardiographic records. Two computer-based measurement procedures fo r characrerizing the repolarization period were comparatively analyzed : Karhunen-Loeve (KL) transform representation of the ST-T shape and m easurement of beat-to-beal durations of repolarization (QT intervals). The results of KL transform representation and time-domain QT measure ment algorithms for studying the repolarization period of the electroc ardiogram on the European ST-T database are presented. II was found th at about 20% of the records present a quasiperiodic KL pattern of isch emic ST-T activity and another 20% exhibit repetitive but not clearly periodic patterns of ischemic ST-T changes. From these ischemic record s, 50% showed QT variations in at least one lead associated with the i schemic episodes.