The history of vectorcardiography.

Vectorcardiography (VCG) is a part of electrocardiography (ECG). The vectorcardiogram displays the various complexes of the electrocardiogram, i.e. QRS, P and T complexes, in the form of "loops" which are determined from vectors representing successive instantaneous mean electric forces from the heart throughout an entire cardiac cycle. Since the heart is a three-dimensional structure, the electric forces from the heart during each heartbeat are oriented three-dimensionally and, therefore, can be represented by a time sequence ofvectors which display the magnitude and direction of these mean electric forces. Anyone who knows the fundamental and theoretical aspects of electrocardiography and knows clinical cardiology and employs electrocardiographs with high frequency response and good fidelity can visualize the detailed configuration of the vectorcardiogram from the electrocardiogram. The electrocardiogram displays the same information as the vectorcardiogram and even provides other information not readily available from the vectorcardiogram, especially temporal phenomena and disorders in cardiac rhythm. Nevertheless, vectorcardiography has developed as a result of the efforts of many investigators who were interested in the use of vector analysis of the cardiac electric potentials recorded from the surface of the body. Such investigations have contributed a great deal to a better understanding of electrocardiography and aspects of electrophysiology. Since the time sequence, magnitude, and spatial direction of the instantaneous mean vectors are determined by the order of depolarization and repolarization of the atria and ventricles which, in turn, are affected by the clinical state of the myocardium, it was considered that the spatial vectorcardiogram could be useful in learning more about the electrophysiology of the heart in normal and diseased states. There have been many reports in the field of vectorcardiography since its introduction (footnotes 1-79). With the recent introduction of a direct-writing vectorcardiograph with good frequency response and fidelity, the use of and interest in vectorcardiography in clinical medicine have increased. Some of the original contributions to vectorcardiography are discussed below.