A New Technique for Monitoring Heart Signals?Part II: Orthogonal Lead Extraction

In Part I, instrumentation design is given for recording ECG signals from a home bathtub setup. In Part II, it is asserted that these bathtub signals are the projections of the heart dipole vector. This assertion is tested and the corresponding coefficients of the projection matrix are computed by monitoring the bathtub ECG signals for a subject as well as his orthogonal X, Y, Z leads on a PDP-9 computer. The least-squares estimation technique is used to determine the projection matrix. To compensate for the magnitude and phase distortion of the bathtub ECG signals, suitable digital as well as analog compensators are designed. A comparison of orthogonal leads extracted from bathtub leads and similar leads obtained from the HP1520A vectorcardiograph is given for five different subjects. It is shown that the average standard deviation obtained for these five subjects is 12.6 percent.