Clinical application of a biomagnetic measurement system with high temperature superconduction quantum interference device

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1)We evaluated whether the cardiac electrical current could be visualized by displaying the current density using a high temperature superconducting quantum interference device (high Tc-SQUID). Magnetic fields from heart were measured using a 32-channel high Tc-SQUID (Sumitomo Electric Hightecs, Co., Ltd.) in a magnetically shielded room. Vector currents were obtained at 32 lead points based on the magnetic gradient, and a current density map were constructed. Current electrical currents were clearly detected during depolarization and repolarization phases. Previously, the detection of magnetic field from the heart required an expensive SQUID system using liquid helium. However, this system was characterized-by its relative higher cost-effectiveness and excellent spatial resolution. In addition, few studies have been done on the map which displays cardiac current density, which can potentially provide important information on electromotive forces. Therefore, this system can be clinical … More ly applied because it facilitates the detection of detailed cardiac electrical current.2)We investigated whether an infarct vector that could not be deduced by electrocardiogram was detectable using isomagnetic and current density map of magnetocardiogram. Old inferior myocardial infarction (15 patients ; MI group) and normal healthy subjects (20 cases ; N group) were recorded with second derivative superconducting quantum interference device (SQUID) magnetocardiometer. Current vector magnitude of each 36 precordial recording point was calculated from magnetic field gradient of adjacent two points. Spline interpolation of precordial current distribution was performed and electromotive force of heart was estimated form current density map. In all subjects in the N group, the QRS vector at 30-40 msec after the onset of QRS wave was directed leftward and inferiorly and multiple dipoles could not be recognized from either surface electrocardiogram, or isomagnetic map. Moreover, in current density map of the ventricular depolarization phase in the N group, one current density was deduced. However, multiple current densities were deduced from the magnetocardiogram of the ventricular depolarization phase in the MI group unlike normal subject. That is, in inferior myocardial patient with abnormal Q wave, the QRS vector at 30-40 msec after the onset of QRS wave was directed superiorly in surface electrocardiogram. On the other hand, the superior QRS vector was deduced in isomagnetic map even in patients with non-Q wave inferior myocardial infarction. In the MI group, multiple current sources were suggested in 4 patients which did not be detected in body surface electrocardiogram. These results suggest that the ventricular depolarization vectors were composed of a normal dipole directed leftward and inferiorly, and an abnormal dipole directed superioly due to inferior myocardial infarction. It is concluded that magnetocardiogram can detect the infarct electromotive force which could not be deduced in electrocardiography. Less