WHY A 3D CARDIOGRAPHIC DISPLAY?
THE OVERLOOKED UTILITY OF A 3D CARDIOGRAPHIC DISPLAY
Many years ago it was anticipated that a 3D display of ECG data would be useful for the analysis of the electrical activity of the heart. Elaborate and expensive devices were created to explore this method of assessment. However, the difficulty and the crudeness of the efforts made it impractical to use and examine patient data. In the 50’s the famous Schmitt of Schmitt trigger fame produced the first stereoscopic image of the electrocardiogram (ref (1)). It was however a novelty, and was never perfected. Even the Vectorcardiogram, which gained some popularity 20 years ago, was not as successful in comparison with the 12 lead as was anticipated. With the facilities of modern computers it is possible to create very useful 3D displays of cardiographic data that reveal properties of these signals that are not observed from the present mix of 12 lead, Vectorcardiogaphic displays or Body maps of multiple electrodes.
The unique capability of a 3D presentation is brought about by the fact that the net vector, for a normal heart, changes smoothly in magnitude and direction as a function of time and is confined to vectors that lie in a single plane. Furthermore the shape of the figure created by the tips of these vectors is appropriately heart like. This shape has been shown in many of the modern textbooks on electrocardiology. (Ref marriot, chou,etc) Thus deviations from the normal are readily apparent, and the variety of deviations can be readily categorized into the well-known disease states. This is due to the ability to physically see the distortion to the normal in 3 dimensions. Thus a loss of muscle tissue in the anterior section of the heart, for example, creates a loss of vectors pointing in this direction, which is readily perceived from the 3 dimensional view. In addition, measurements can be made that relate to the 3D characteristics of the data, such as the angle of the horizontal angle of the perpendicular to the plane of vectors, which for the normal heart is on average parallel to the x axis. The angle of this plane from the horizontal also falls into a narrow range of narrow range centered at 40 degrees with a standard deviation of 14.7 degrees. The time to change from ½ the magnitude of the maximum vector to maximum and then decrease to ½ maximum is also a powerful measure of normality. These new measurements provide another means to differentiate the diseased heart from the normal.
Ref 1. "A Hundred Years of Progress in Electrocardiography 2: The Rise and Decline of Vectorcardiography" The Canadian Journal of Cardiology 4(2):60 1988