Visualization of atrial excitation by magnetocardiogram.

We tried to visualize normal atrial excitatory process by magnetocardiogram (MCG) measured from both anterior chest and back using our newest multi-channel SQUID system. Twenty normal subjects were studied. After measuring the normal (B(z)) component of the magnetic field, we constructed an isomagnetic and vector arrow map from spatial derivatives of the normal (B(z)) component in the tangential direction. By the MCG measurement from the anterior chest, current arrows were recognized in the right upper portion which were directed to the left lower from the beginning of the P wave to the P-wave peak. By the measurement from the back, current arrows were able to be visualized in the right to middle upper portion which were directed to the left or left lower just before the P-wave peak. We conclude that we successfully recognized the right atrial excitation and its spread to the left atrium and observed the time course of normal atrial excitatory process by the MCG measurement from not only anterior chest but also back using 64-channel SQUID system.