Two-dimensional mapping of impedance magnetocardiograms

Area of Science:

• Biophysics
• Cardiovascular Physiology
• Biomedical Engineering

Background:

• Magnetocardiography (MCG) measures the magnetic fields produced by cardiac electrical activity.
• Impedance cardiography (ICG) measures electrical impedance changes related to cardiac function.
• Simultaneous measurement of both MCG and ICG could provide complementary physiological information.

Purpose of the Study:

• To develop and validate a new method for simultaneously measuring 2-D impedance magnetocardiograms (I-MCGs) and magnetocardiograms (MCGs).
• To investigate the physiological information provided by the novel 2-D I-MCG technique.
• To assess the potential of 2-D I-MCG for understanding cardiac circulatory movements.

Main Methods:

• Developed a system using a superconducting interference device (SQUID) to record both I-MCG and MCG signals.
• Employed four first-order gradiometers and a flux-locked-loop circuit driven by a 40 kHz AC current.
• Filtered and demodulated signals to isolate I-MCG, reflecting conductivity changes due to heart muscle and blood volume movement.

Main Results:

• The 2-D I-MCG signals showed maximal amplitude over the right ventricle and right atrium.
• Current-arrow mapping indicated significant current flow over the right side of the right ventricle.
• Discrepancies were observed between systole/diastole timings derived from I-MCG and phonocardiograms.

Conclusions:

• The developed 2-D I-MCG method successfully measures cardiac conductivity changes.
• 2-D I-MCG provides valuable physiological data on cardiac circulatory dynamics.
• This technique holds promise for enhanced understanding of heart function and potential clinical applications.