The magnetic heart vector.

Abstract Records of the magnetic field due to the heart can be obtained in a hospital environment without the use of a magnetically shielded room. It is possible to build a magnetocardiograph sensitive primarily to the tangential components of the heart's EMF's. This is in contrast to ECG's where the radial component is emphasized and usually masks any tangential components. Tangential EMF components lying in frontal planes cause current to circulate around the front-to-back (z) axis, and can be assigned a vector direction along this axis. Similarly, tangential EMF's in sagittal and horizontal planes can be associated with x and y directed vectors. The vector sum of these three components is the spatial “magnetic heart vector.” The magnetic heart vector is conceptually similar to, and can be displayed using the same techniques as, the “heart vector” of electrovectorcardiography but is of radically different interpretation. Ideal magnetocardiographic leads, analogous to ideal electrovectorcardiographic leads, are defined in terms of the lead fields produced. Our present magnetocardiograph, while not specifically designed to implement the ideas of this paper, does give evidence that there are some tangentially oriented EMF components in persons without heart disease, and often much larger tangential EMF's in persons with heart disease.