Effects of Body Surface Boundary and of Tissue Inhomogenelty on the Electrocardiogram of the Dog

The voltage-current relationship between intrathoracic ‘dipoles’ and body surface locations was examined in anesthetized dogs. Controlled currents were applied at body surface points, and potentials were recorded at the intrathoracic dipoles. A technique of fastening the electrodes to a cast made on the animal's torso permitted exact measurement of the torso and electrode geometry. The potentials recorded in the animal were compared with (1) an infinite-medium simulation performed on a digital computer, (2) a bounded- medium simulation performed in the plaster cast of each torso studied, and (3) a simulation involving a torso model containing heart and lungs. The correlation between recorded and simulated potentials was fair for the infinite-medium simulation, improved by the boundary, and further improved by the addition of inhomogeneity. Implications for electrocardiography are discussed.