A simple method to determine the state of ischaemia or fibrosis of myocardial cells has been developed. This method uses the ST wave of 64-channel magnetocardiogram (MCG) signals to calculate three parameters from the current-arrow map of the normal component signal of the MCG. One parameter is a total current vector that is obtained through summation of all current arrows. Another is a variance current vector calculated from the differential vector of two total current vectors at different times. The third is a flatness factor between the magnitude of the total current vector and the variance current vector. The three parameters are independent of the distance between the heart and the gradiometers. We measured the MCG signals of 29 healthy subjects, twenty patients with coronary artery disease (ten with previous myocardial infarction (MI) and ten with angina pectoris (AP)), and eight patients with cardiomyopathy (four with hypertrophic cardiomyopathy (HCM), three with dilated cardiomyopathy (DCM), and one with restrictive cardiomyopathy (RCM)). With our method, none of the healthy subjects tested positive for myocardial abnormalities, while 80% of the MI patients, 50% of the AP patients, and 100% of the cardiomyopathy patients tested positive. Although further testing is needed, we feel this simple technique enables easy diagnosis of myocardial damage.

No abstract

To determine the developmental changes in the myocardial current during fetal life, and to evaluate the clinical usefulness of magnetocardiography for prenatal diagnosis of cardiac hypertrophy or enlargement, we approximated the magnitude of the one-current dipole of the fetal heart using fetal magnetocardiography (fMCG). A total of 95 fetuses with gestational age of 20 -40 wk were included in this study. fMCG was recorded with a nine-channel superconducting quantum interference device system in a magnetically shielded room. The magnitude of the dipole (Q) was calculated using an equation based on the fMCG amplitude obtained on the maternal abdomen and the distance between the maternal surface and fetal heart measured ultrasonographically. In uncomplicated pregnancies, the Q value correlated significantly with gestational age, reflecting an increase in the amount of myocardial current, i.e. myocardial mass. Moreover, the Q values in fetuses with cardiomegaly caused by various cardiovascular abnormalities tended to be higher than the normal values. Although there are some limitations of the methodology based on the half-space model, and fetal orientation may influence the magnitude of the dipole, making it smaller, fMCG recorded with a multichannel superconducting quantum interference device system is a clinically useful tool for noninvasive, prenatal, and electrical evaluation of fetal cardiac hypertrophy. (1) in 1974, the magnetic field generated by the fetal heart has been measured noninvasively with satisfactory waveforms. MCG requires no pasting of electrodes to the fetal body surface and is completely noninvasive to both fetus and mother. MCG signals from the fetal heart are considered to be minimally affected by the electrical conduction properties of the tissue around the heart (2, 3). In fact, time intervals can be obtained with satisfactory signal-to-noise ratio even after the development of vernix caseosa in the second half of gestation. A number of studies, including ours, defined the developmental changes and normal ranges of various time intervals on the fMCG in uncomplicated pregnancies (4 -6). However, the amplitude of the fMCG waveform has not been fully investigated (7), although it is another important variable used for the diagnosis of fetal heart diseases. One reason for this rare application is that the amplitude of fMCG measured on the maternal abdomen does not necessarily reflect the maximum value of myocardial current because of the effects of the depth and orientation of the heart. Furthermore, these biases are not easily corrected as the fetus may move during measurement.We attempted to approximate the magnitude of the onecurrent dipole of the fetal heart based on the maximum value of fMCG data obtained with a multichannel SQUID system and the depth of the fetal heart determined by echocardiography in normal pregnancies. We then used these control values to assess magnitude abnormalities in fetuses with cardiomegaly resulting from excessive volume loading in cardiac ventricles. Using bo...

We have developed a 64-channnel superconducting quantum interference (SQUID) system that can analyze the vector components of a cardiac magnetic field, and that is more compact and requires fewer SQUID sensors and measuring circuits than existing systems. To adjust the position of the dewar, containing sensor array and liquid He relative to the chest, the bed is capable of threedim ensional movement. The "ma& 'ogram (MCG) data from the 64 channels are stored and analyzed using a personal computer. Each measurement site contains first-order gradiometers to detect the Bz component on the torso. The typical noise of the system in a magnetically shielded room (MSR) is less than 20 ff/ h. Tangential components at each measuring site can be calculated fiom the ht-order gradient of Bz in the x-and ydirections. Two types of magnetic-field patterns of the Bz component and the Bxy tangential components are obtained at the same time. The position and distribution of a current source in the heart can be visualized through a twodimensional projection usnig the analyzed tangential magnetic field.

The aim of this study is to detect the spatial current dispersion that appears in the T-wave of patients with congenital long-QT syndrome (LQTS). To observe this dispersion, magnetocardiograms (MCGs)--which have a high spatial resolution--of LQT1 patients (n = 7), LQT2 patients (n = 9) and a control group (n = 33) were recorded. The dispersion was evaluated by plotting current-arrow maps (CAMs) calculated from the MCG signals. In the case of LQT1, abnormal current arrows in the CAMs appeared above the inferior part of the heart in two LQT1 patients with a long corrected QT interval (QTc) (>0.6), and the current direction was from the left (origin side) to the right ventricular muscle (110 degrees). In six out of nine LQT2 patients, abnormal current arrows with angles below 20 degrees were observed above the right inferior part or lower septum; the current direction was from the right (origin side) to the left ventricular muscle. However, in the case of the LQT2 patients, the QTc values did not correlate with the abnormal current. These findings suggest that the origin of abnormal repolarization in LQT1 is the left ventricular muscle and the origin of that in LQT2 is the right ventricular muscle or lower septum. The estimation of the origin in LQTS patients can provide important information such as the risk factor of sudden death.