“Aimed” electrocardiography. Model studies, using a heart consisting of 6 electrically isolated areas

Abstract With the exception of the McFee-Johnston null leads, the voltages in electrocardiographic leads are due to synchronous electromotive forces in all parts of the heart. This applies to bipolar and "unipolar" conventional leads and to all available orthogonal and vectorcardiographic lead systems. "Aimed" electrocardiographic leads, on the other hand, are defined in the present paper as responding to electromotive forces in a limited cardiac area, while being insensitive to forces in other regions of the heart. A three-dimensional model of the human torso and the heart was built. The model heart was a cast of the 4 cardiac chambers. In the living heart, intracardiac blood represents a region, the conductivity of which is finite, homogeneous, and higher than that of the torso, whereas, for reasons stated, the heart model consisted of insulating material with a surface coating of infinite conductivity. The coating was divided, by nonconducting strips, into 1 atrial and 5 ventricular areas. The torso was otherwise homogeneous. Eight brass screws, representing electrodes placed as in the Z lead of the SVEC-III lead system, penetrated the wall of the torso. A method for calculating the dipole moment of each of the cardiac areas, from the voltages appearing at the 8 electrodes, is given in detail. A simple network which automatically performs the calculations, and thus is able to supply a standard electrocardiogram with voltages due to each of 5 ventricular areas, is described. Some discrepancies between the model and the living heart which are likely to cause errors that impair the clinical usefulness of the method are listed, and means of reducing error are discussed.