Detection of cardiac hypertrophy in the fetus by approximation of the current dipole using magnetocardiography.

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.

Signal-averaged electrocardiogram in children and adolescents with insulin-dependent diabetes mellitus.

UNLABELLED: We report on the potential usefulness of the signal-averaged electrocardiogram (SA-ECG) in young patients with insulin-dependent diabetes mellitus (IDDM) to predict subclinical cardiovascular complications. Sixteen patients with IDDM and 18 age-matched healthy subjects were studied. The IDDM group included 4 males and 12 females, aged 7 to 20 y (mean 14.2 +/- 3.8 y, +/- SD). The duration from the onset of IDDM to the study ranged from 1.2 to 9.8 y (mean 5.4 +/- 3.8 y), and HbAlc value ranged from 6.6 to 12.4% (mean, 10.0 +/- 1.8%). SA-ECG was recorded and analyzed using the methods described by Simson. Values of filtered QRS duration (f-QRS), root mean square voltage (RMS), the duration of low amplitude signal (LAS) and late duration (LD) were calculated and compared between the groups. These parameters were not significantly different between the IDDM and control groups. However, in patients with poor glycemic control (HbAlc >10%), f-QRS was long and RMS was significantly low (p < 0.05, each) compared with the control group. Three patients with IDDM were positive for ventricular late potentials, although none had ventricular tachyarrhythmia. None of the control subjects showed ventricular late potentials. CONCLUSION: Certain parameters of SA-ECG showed abnormal values in IDDM patients with poor glycemic control. Thus, SA-ECG is a potentially useful and non-invasive method for the assessment of subclinical cardiac impairment in diabetic children and adolescents.

An iso-integral mapping technique using magnetocardiogram, and its possible use for diagnosis of ischemic heart disease.

We have developed an iso-integral mapping technique that uses magneto-cardiogram (MCG) data to obtain a map as projected total current image on the torso from the heart. We have also investigated the applicability of iso-integral mapping to the diagnosis of ischemic heart disease. We simulated and measured the characteristics of two types of iso-integral maps: one using tangential (Bxy) components, and one using the normal component (Bz). Each vector component was measured by two types of superconducting quantum interference device (SQUID) system to determine the tangential and normal components. The tangential component of the magnetic field appeared to be equivalent to the current image in the myocardium projected on the observing plane, and we were able to obtain a projected total current image by integration of the tangential components during the depolarization and repolarization processes. And we found that the iso-integral maps of normal hearts showed similar pattern in both processes; however, those of ischemic hearts showed different patterns.

Visualization of regional myocardial depolarization by tangential component mapping on magnetocardiogram in children.

BACKGROUND: Tangential components to the body surface on magnetocardiography theoretically reflect regional myocardial current sources just below the gradiometer. The usefulness of tangential component mapping on magnetocardiography in determination of regional myocardial abnormalities has not been investigated in children. METHODS: Twenty-six children with ventricular hypertrophy, including a child with a left ventricular diverticulum (aged 7 to 15), and age matched 22 healthy children (aged 7 to 15) were studied. Tangential components on magnetocardiography were measured using a newly-developed super-conducting quantum interference device system housed in a magnetically shielded room. Isomagnetic maps and current vector maps were constructed from the data obtained. RESULTS: The peak magnetic fields and current dipoles were demonstrated to be located at the interventricular septum initially, and then were shifted to the anterior and inferior walls of the left ventricle and to the right ventricular outflow tract, successively. In patients with right ventricular hypertrophy whose systolic right ventricular pressure was over 60 mmHg, the peak magnetic fields were located in the right half with rightward directed current vectors throughout ventricular depolarization. In patients with left ventricular hypertrophy, the maximal magnetic fields during depolarization were shifted to the hypertrophic site, showing significantly stronger forces than those in healthy children (35.5+/-11.7 pT vs 26.5+/-11.9 pT, p < 0.01). In a patient with left ventricular diverticulum, two discrete depolarizing current dipoles were visualized. The mean time required in measuring MCGs among all subjects was 10 minutes. CONCLUSION: The time course as well as the location of the regional electrical activities of the myocardium in children can be visualized, in a short time, as a two-dimensional projection to the frontal plane by tangential component mapping on magnetocardiography.