Detection of myocardial ischemia by magnetocardiogram using 64-channel SQUID system

Ischemic heart disease (IHD) is one of the most critical diseases in view of its serious mortality and frequency of occurrence. Especially in Japan, aging population and recent changes in life styles, such as increasing intake of animal fat, are expected to bring about a more frequent occurrence of atherosclerotic lesions in coronary arteries, resulting in an increased IHD morbidity. Furthermore, we can now see more IHD in younger population. Therefore, accurate and quick diagnosis is important. For early detection of IHD, a non-invasive and convenient diagnostic tool with reasonably high accuracy is needed. From this point of view, resting standard electrocardiography (ECG) and echocardiography, which are standard non-invasive diagnostic tools, are not satisfactory in the diagnosis of IHD. The electrical current generated by the heart creates not only electric potential but also a magnetic field. We have observed electrophysiological phenomena of the heart by measuring tangential components of magnetocardiograms (MCGs) using a multi-channel superconducting quantum interference device (SQUID) system [1]. Using the tangential components, we have obtained a two-dimensional current projection pattern on the observing plane, because these components show a peak pattern just above the current source. We have developed vector arrow maps of the current from tangential MCGs and have observed their time courses in normal subjects and various patients with cardiac diseases [2,3,4]. We have also developed a visualization method, iso-integral mapping, that is used for twodimensional visualization of total current distribution during the depolarization and repolarization of the ventricle [5]. With our multi-channel SQUID system and these two visualization methods, we thought we may be able to use MCGs as an absolutely non-invasive and convenient diagnostic tool for IHD. In this study, we tried to visualize myocardial ischemia by measuring MCGs using a 64-channel SQUID system, and compared the effectiveness of this approach to resting standard 12-lead ECG and echocardiography.