Dielectric properties of canine acute and chronic myocardial infarction at a cell relaxation spectrum. II. Theory

A new model of bulk myocardium dielectric properties as a composition of membrane covered cells modelled as infinite cylinders has been developed. This model utilizes the complex values of dielectric properties of the intracellular, extracellular media and the cellular membrane. The model was used to analyze the myocardial resistivity above and below the cell membrane relaxation spectrum in normal myocardium and in acute and chronic infarction. This myocardium cell model gives reasonable qualitative explanation not only for the spectrum of normal myocardial resistance but also for observed changes in the spectrum of myocardial resistance in acute ischemia and chronic infarction based on the "volume fraction hypothesis". The contributions of intracellular, extracellular and cell membrane resistances to bulk myocardial resistance are frequency dependent. At frequencies below 0.2 MHz the intracellular contribution to bulk resistance is much smaller compared to the extracellular resistance and does not exceed 10-15%. At frequencies higher than 0.5 MHz the measured bulk resistance reflects extracellular and intracellular resistances at about the same order. The contribution of the cell membrane resistance is much smaller compared to the intracellular and extracellular resistances and does not exceed 0.1% at frequency near 1 Hz for normal myocardium.