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 superconducting 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: he 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.