A comparison of volume conductor and source geometry effects on body surface and epicardial potentials

Using an analytical mathematical model, we studied and contrasted the effects of variations in geometry and volume conductor properties of the torso on epicardial and body surface potentials. The model consists of a spherical heart (blood cavity bounded by a spherical muscle shell that includes a double layer source, and pericardium) eccentrically placed in a spherical torso (lung region bounded by muscle and fat layers). The effects of the following parameters on body surface and epicardial potentials were studied: (1) separation of the cardiac sources; (2) location of the heart within the torso; (3) combined effects of all torso inhomogeneities, (4) 'internal' inhomogeneities (intracavitary blood, pericardium); (5) 'external' inhomogeneities (lung region, skeletal muscle, subcutaneous fat), and (6) hypertrophy and dilation. It was determined that, although internal inhomogeneities affect both epicardial and surface potentials similarly, the effect of external inhomogeneities on body surface potentials is different from their effect on epicardial potentials. The effects of hypertrophy and dilation are seen to depend on specific details regarding alterations in size and shape of blood cavity, heart, and activation surface. The most important conclusion of the study is that epicardial potential maps accurately reflect the underlying source configuration, are free of the effects of body shape and size, and are affected significantly by only one extracardiac inhomogeneity - namely, the lung region. Such maps, therefore, can enhance our capability to interpret and diagnose electrophysiological events within the heart.