Submitted on November 8, 2005
Accepted on December 19, 2005
Cardiac micro-impedance measurement in two-dimensional models using multisite interstitial stimulation
Andrew E Pollard1* and Roger C Barr2
1 Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL, USA
2 Biomedical Engineering, Duke University, Durham, NC, USA
* To whom correspondence should be addressed. E-mail: pollard{at}crml.uab.edu.
We analyzed central interstitial potential differences during multisite stimulation to assess the feasibility of using those recordings to measure cardiac micro-impedances in multidimensional preparations. Because interstitial current injected and removed using electrodes with different proximities allows modulation of the portion of current crossing the membrane, we hypothesized that multisite interstitial stimulation would give rise to central interstitial potential differences that depended upon intracellular and interstitial micro-impedances, allowing measurement of those micro-impedances. Simulations of multisite stimulation with fine and wide spacing in two-dimensional models that included dynamic membrane equations for guinea pig ventricular myocytes were performed to generate test data (
o ). Isotropic interstitial and intracellular micro-impedances were prescribed for one set of simulations, while anisotropic micro-impedances with unequal ratios (intracellular/interstitial) along and across fibers were prescribed for another set of simulations. Micro-impedance measurements were then obtained by making statistical comparisons between o values and interstitial potential differences from passive bidomain simulations (
o) in which a wide range of possible micro-impedances were considered. Possible micro-impedances were selected at 25% increments. Following demonstration of the effectiveness of the overall method with micro-impedance measurements using one-dimensional test data, we showed micro-impedance measurements in both the isotropic and anisotropic models that were within 25% of prescribed values. Our findings suggest development of microfabricated devices to implement the procedure would facilitate routine measurement as a component of cardiac electrophysiologic study.
