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The vector principle is the basic principle of electrocardiography for the interpretation of the standard 12-lead electrocardiogram (ECG) as well as for teaching.1 However, its application in the interpretation of the standard 12-lead ECG is demanding for a mental three-dimensional imagination, and the "mental image" requires linking the orientation and magnitude of the vector to the anatomy of the heart, its position in the chest, and the sequence of activation (Fig. 11–1).
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Vectorcardiography partially reduces these problems. It presents the distributed electric field at every instant of time by a dipole—the equivalent dipole. This dipole is represented by a vector, defined by its magnitude and orientation, theoretically corresponding to the extent of the activation front and its location. The origin of the dipole is fixed in the center of an orthogonal coordinate system, and the trajectory of the end point of the vector during the atrial/ventricular depolarization and repolarization depicts the spatial vectorcardiographic loop. The classical graphical presentation of vectorcardiography is the planar vectorcardiogram—the planar projection of the spatial vectorcardiographic loop onto three perpendicular planes: the frontal, sagittal, and horizontal (transverse) planes.
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Compared with the standard 12-lead ECG, the orthogonal ECG does not contain redundant information. The coordinate system of the orthogonal ECG/vectorcardiogram may be aligned with the geometry of the heart and to our knowledge about the sequence of atrial and ventricular activation. These characteristics make the vectorcardiogram instrumental for teaching the principles of ECG diagnosis, as well as for comparative studies with other imaging methods. However, the interpretation of vectorcardiograms is demanding for three-dimensional imagination and for good orientation in the anatomic structures and their relationships to the processes in the heart. In addition, these graphical presentations—scalar tracings of orthogonal ECG and planar vectorcardiogram—are not directly comparable with images of the heart developed from another imaging method.
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In this chapter, we describe a method for graphical presentation of the orthogonal ECG/vectorcardiogram that allows the visualization of the vectors representing the cardiac electrical field comparably to other imaging methods used in cardiology. This graphical presentation of ECG is suitable for side-to-side comparisons as well as for superimposition or fusion of information from multiple imaging modalities.
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Dipolar Electrocardiotopography
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In dipolar electrocardiotopography (DECARTO), the orthogonal ECG is transformed to areas projected on a spherical image surface. The original DECARTO model2,3 was developed for the presentation of the ...