Measurement of myocardial conductivities with a four-electrode technique in the frequency domain

Bidomain conductivities are evaluated from extracellular measurements on canine myocardial tissue with a modified four-electrode technique. The probe consists of two orthogonal rows of four electrodes with a suitable spacing for sampling the intracellular and interstitial conductivities. A subthreshold sinusoidal current (12 Hz to 2400 Hz) is applied to the outermost electrodes of one row. Potential difference is measured between the innermost electrodes. A drug with uncoupling properties is injected and modifications in conductivities are detected after injection. The longitudinal and transverse potential measurements are fitted with a numerical three dimensional bidomain model with no restriction on the longitudinal to transverse anisotropy ratio.