Visualization of cardiac dipole using a current density map: detection of cardiac current undetectable by electrocardiography using magnetocardiography

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  • Ikefuji Hiroyuki
    Department of Cardiology, JA Kochi Hospital
  • Nomura Masahiro
    Faculty of Integrated Art and Sciences, Department of Human and Social Sciences, The University of Tokushima
  • Nakaya Yutaka
    Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Mori Toshifumi
    Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Kondo Noriyasu
    Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Ieishi Kiyoshi
    Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Fujimoto Sayuri
    Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School
  • Ito Susumu
    Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School

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Abstract

A close relationship exists between electric current and the magnetic field. However, electricity and magnetism have different physical characteristics, and magnetocardiography (MCG) may provide information on cardiac current that is difficult to obtain by electrocardiography (ECG). In the present study, we investigated the issue of whether the current density map method, in which cardiac current is estimated from the magnetic gradient, facilitates the visualization of cardiac current undetectable by ECG.<BR>The subjects were 50 healthy adults (N group), 40 patients with left ventricular overloading (LVO group), 15 patients with right ventricular overloading (RVO group), 10 patients with an old inferior myocardial infarction (OMI group), and 30 patients with diabetes mellitus (DM group). MCGs were recorded with a second derivative superconducting quantum interference device (SQUID) gradiometer using liquid helium. Isopotential maps and current density maps from unipolar precordial ECG leads and MCGs, respectively, were prepared, and the cardiac electric current was examined.<BR>The current density map at the ventricular depolarization phase showed one peak of current density in the N group. However, in the OMI group, the current density map showed multiple peaks of current density areas. In the RVO group, two peaks of current densities were detected at the right superior region and left thoracic region and these two diploles appeared to be from the right and left ventricular derived cardiac currents, respectively. Moreover, there was a significant correlation between the magnitude of the current density from the right ventricle and the systolic pulmonary arterial pressure. The current density map at the ventricular repolarization phase in the N group showed only a single current source. However, abnormal current sources in the current density maps were frequently detected even in patients showing no abnormalities on isopotential maps in the LVO, DM, and OMI groups.<BR>The findings herein suggest that opposing dipoles of the ventricular depolarization and repolarization vectors were summed and evaluated as a single dipole in the electrocardiogram. However, MCG facilitated the detection of multiple dipoles because of its superior spatial resolution as well as difference in physical properties between magnetic and electrical fields. Our results suggest that MCG with a current density map is useful for detecting cardiac current undetectable by ECG in an early stage. J. Med. Invest. 54: 116-123, February, 2007

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