REPRESENTATION AND ANALYSIS OF SIGNALS. PART VIII. REPRESENTATION OF ELECTROCARDIOGRAM BY ORTHOGONALIZED EXPONENTIALS

Electrocardiography has proved to be a useful diagnostic aid for physicians. There is a growing interest in the statistical study of electrocardiograms. A prerequisite for this is to transform the analytic ECG waveform efficiently into a numerical representation. In this paper, a method is given for characterizing each ECG waveform by a few numbers. We show that a typical ECG waveform may be expressed as the sum of a small set of exponential components, the amplitude of which describe the signal vector in an orthogonal signal space. Thus each entire ECG wave corresponds to a single fixed vector in this abstract signal space. This compact numerical representation may be used for further statistical study and analysis. The instrumentation for measuring the coordinates of these signals on an orthogonalized exponential basis will be described and experimental results given showing the accuracy achieved by ten to twenty components. The orthogonal signal space representation may be used to express the vectorcardiographic idea. Ordinarily, vectorcardiograms are projected in xy, yz and zx planes. By means of the well-known eigenvalue process, we were able to find the major loop of QRS complex and the plane on which it lies. The eigenvectors calculated in this way may, if we wish, provide a basis for ECG comparison instead of the conventional x, y, z components. (Author)