The feasibility of transoesophageal bioimpedance measurements for the detection of heart graft rejection

Abstract

Previous studies demonstrate that it is possible to evaluate a heart graft rejection condition using a bioimpedance technique by means of an intracavitary catheter. We propose to use a less invasive technique consisting in the use of a transoesophageal catheter and two standard ECG electrodes on the thorax. The aim of this work is to evaluate, using the finite element method, several parameters affecting the transoesophageal impedance measurement, including sensitivity to electrical conductivity and permittivity of different organs in the thorax, changes in magnitude and phase due to a lesion producing a scar, a global ischaemia of the heart, pleural effusion in the lungs, fat thickness increase, displacement of the catheter inside the oesophagus and movement of one electrode on the thorax surface. From these results, we deduce the best estimator for cardiac rejection detection and obtain the tools to identify eventual cases of false positives due to other factors. To achieve these objectives we have created a thoracic model and we have simulated different situations at the frequencies of 13, 30, 100, 300 and 1000 kHz. Our simulation demonstrates that the phase, at 100 and 300 kHz, would be a better estimator than the magnitude to evaluate a heart rejection condition.