Impedance spectroscopy: a method for surveillance of ischemia tolerance of the heart

During myocardial ischemia the phase angle phi of the complex electric impedance of myocardial tissue at 5 kHz AC exhibits a characteristic behaviour, the progress of which depends on the cardioplegic method applied. By extending the frequency range to 200 Hz and 10 MHz and by analyzing in addition to phase and magnitude also real and imaginary part of the impedance it was possible to elucidate which ischemic changes in the myocardium are responsible for the course of phi (5 kHz). This method we call impedance spectroscopy. Canine hearts were cardioplegically perfused with either the standard solution HTK[4] or the solution HTK[4] + 50 mumol/l Ca++. During the following ischemia at 25 degrees C energy-rich phosphate level, the ultrastructure, the real part, imaginary part and phase angle of the impedance between 200 Hz and 10 MHz were analyzed.

phi (5 kHz) displays very similar characteristics during the ischemic period to those of the real part of the impedance at 200 Hz, Re (200 Hz). Re (200 Hz) increases, when--according to electron microscopic findings--an intracellular myocardial edema begins to develop. The changes of Re(200 Hz) are always smaller, however, than those of phi (5 kHz). This indicates that phi (5 kHz) increases in the course of ischemia not only as a consequence of confinement of the extracellular space by myocardial cellular edema but also because of changes of passive electrical characteristics of the myocardial cell membranes.(ABSTRACT TRUNCATED AT 250 WORDS)