Analysis of the cardiac repolarization period using the KL transform: applications on the ST-T database

The ST-T segment of the surface ECG reflects cardiac repolarization, and is quite sensitive to a number of pathological conditions. ST-T changes generally affect the entire waveshape, and are inadequately characterized by single features such as depression of the ST segment. Metrics which represent overall waveshape should provide more sensitive indicators of ST-T wave abnormalities. This study presents a Karhunen-Loeve Transform (KLT) technique for the analysis of the ST-T waveform. This technique recovers maximum information from a minimum number of parameters for a given set of waveforms. The training data yielded a KL basis set which concentrates 90% of the ST-T signal energy in the first four coefficients. The KL technique was used to analyze the ST-T complexes in the ESC ST-T database. KL coefficients were plotted as a function of time, and were effective in detection of transient ischemic episodes. Twenty percent of the records showed bursts of periodic ischemia suggesting local vascular instability.<>