Electrical alignment of a cardiac impedance probe

The authors propose a method to align the electrodes of a cardiac impedance probe with respect to the myocardial fibers without using microscopic observations. The method relies on the fact that the injection of current at a point in cardiac tissue generates an ellipsoidal potential distribution. By modifying the standard 4-electrode technique to incorporate an additional pair of potential measuring electrodes the authors are able to measure the potentials in a direction perpendicular to the row. Null potentials on the perpendicular electrodes indicates that the probe is parallel or perpendicular to the fibers. The method war tested using a bidomain and anisotropic model of the myocardium. A current of 1 μA was applied between the outer electrodes of the standard row and the extracellular potentials were computed. Rotation of the probe was then simulated and the potentials calculated on the perpendicular electrodes as well as the inner electrodes of the standard row were plotted with respect to the angle of rotation. These curves clearly show that the potential between the perpendicular electrodes is equal to zero when the probe is perfectly aligned with either the longitudinal or the transverse directions. Discrimination between these two directions is obtained by measuring the potentials between the inner electrodes of the standard row, which are larger in the longitudinal direction