Electrical Alignment of a Cardiac Impedance Probe

E Plourde, P Savard, P Le Guyader

Institut de génie biomédical

École Polytechnique de Montréal

Montréal, Canada

September 27th, 2000

Electrical Alignment Of A Cardiac Impedance Probe

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Presentation

• Introduction

• Traditional aligning method

• Electrical alignment of the cardiac impedance probe

• Results

• Conclusion

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Electrical Alignment Of A Cardiac Impedance Probe

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Introduction

• Measurements of the myocardial passive electrical properties

• Usually made with the four-electrode technique

• The probe must be aligned

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Electrical Alignment Of A Cardiac Impedance Probe

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Traditional aligning method

• Usually aligned by visual inspection

• Problems encountered with the traditional aligning method:– in in vivo studies– if the fibers are not within the visual range of

the experimenter

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Electrical alignment of the cardiac impedance probe (1)

• Modified 4-electrodes technique

• Additional pair of perpendicular potential recording electrodes

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Electrical alignment of the cardiac impedance probe (2)

• Why add two perpendicular potential electrodes?– Symmetrical ellipsoids potential distribution

separated by a line of null potentials

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Potential distribution for current injected parallel to the fibers

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Potential distribution for current injected perpendicular to the fibers

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Potential distribution for oblique current injection

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Results - Simulation (bidomain anisotropic model)

• Rotation of the probe• Null potentials at 0o

and 90o

• Discrimination between the longitudinal and transverse orientations

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Results -Experimentation• In preliminary results

– observed potentials near zero on the perpendicular electrodes followed by maximums (0,09mV) at each 90 degrees of rotation

– observed greater potentials in the longitudinal (0,7mV) than transverse orientation (0,65mV)

• Noise problems due to the small potentials measured

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Conclusion

• The method takes advantage of the anisotropy of the myocardium to align the probe

• It is feasible to align the probe without relying on visual inspection

• The method will be used in in vivo studies and on probes placed at the tip of a catheter