Local Myocardial Perfusion Monitored by Electrical Resistivity -an Exploratory Technique-

Abstract

Abnormal conduction and electrocardiographic patterns following myocardial ischemia are related to changes in electrical properties of the myocardium. The local electrical resistivity of the myocardium influences the shape and velocity of the excitation wave [1–3]. The anatomical structure of the myocardium reveals inhomogeneities which may be reflected in its electrical properties. At microscopic level (10–100 µm), the intracellular medium, the extracellular medium, the muscle fiber membrane and the blood containing capillaries all possess distinct electrical properties. At a larger scale (100–1000 µm) the muscle fibers and vasculature are organized such that anisotropic properties can be anticipated. It has indeed been known since Rush’s work [4] that macroscopic (i.e. scale 1–10 mm) resistivity in the muscle fiber direction (ρ l , longitudinal resistivity) is lower than resistivity perpendicular to that direction (ρ t , transverse). Many investigators confirmed this finding, but the reported values for ρ l and ρt vary considerably among authors. First, this variation may be due to different conditions of the preparations. Van Oosterom [5] showed that myocardial resistivity measured transmurally changes dramatically when local ischemia is induced. Wojtczak [6] demonstrated changes in passive electrical properties of cow ventricular muscle with hypoxia. Second, resistivities were studied at different frequencies.