Importance of the tissue conductivity values in modelling the thorax as a volume conductor

Various thoracic inhomogeneities affect the measured surface ECG signal. Similarly when the conductivities of these inhomogeneities change the ECG may change as well. Conductivity of tissue may change due to variation in body water and electrolyte balance e.g. due to many diseases. Furthermore, there exits uncertainty regarding the correct values of tissue conductivities and their inter- and intrapatient alterations. Thus the effects of these changes on the ECG signal parameters and on the forward and inverse ECG problem may be of importance. An accurate thorax model based on finite difference method featuring the anatomy of the Visible Human Man was developed. The effects of conductivity changes were determined by increasing the conductivity by 10%-a change that can be of physiological origin. X, Y and Z components of a current dipole source located at the center of the heart were energized and corresponding ECG signals were determined. Results indicated that physiological changes of tissue conductivity produced marked changes in ECG signal, which should be considered in modelling and in ECG analysis. The results manifested the importance of the correct conductivity values. When constructing accurate models of human thorax as a volume conductor the correct tissue conductivities may be more important than the accuracy of anatomical features.