Fetal atrial load and prognosis assessed by a new index in magnetocardiography

FFetal magnetocardiogram (FMCG) is a non-invasive recording of faint magnetic signals produced by electrical activity of the fetal heart, and thus has been applied to various prenatal diagnoses in fetal cardiology especially in the diagnoses of fetal arrhythmia. However information on amplitudes of FMCG components has rarely been examined. In this study, we evaluated the P wave of FMCG of fetuses complicated by congenital heart diseases using a new quantitative index in FMCG, modified DIrot (mDIrot), at P wave. We recorded 2-min FMCG from 34 fetuses (13 normal fetuses and 21 fetuses with congenital heart diseases) using a 64-channel SQUID system installed in the National Cardiovascular Center in Japan. The sensors were arrayed in an 8×8 arrangement with an interval of 2.5 cm. The sensor arrays were positioned just above the fetal heart. We averaged the FMCG signals using R-wave peaks as a trigger, and then generated a current arrow map (CAM), which showed the distribution of the magnetic field. Hypothetical heart currents that produced magnetic distributions were calculated using partial differentiation of FMCG signals. The sums of rotating components of the current vectors at each point in the CAM were calculated. Modified DIrot was defined as the difference between the maximum and the minimum of the sums. The mDIrot at P wave of FMCG in two cases of pulmonary atresia and pulmonary stenosis in fetuses with congenital heart diseases were significantly larger than the averaged mDIrot of normal fetuses. The mDIrot at the P wave of FMCG in tetralogy of Fallot was also larger than the normal averaged mDIrot. The prognoses of the neonates with pulmonary atresia and pulmonary stenosis, which complicated with excess atrial load, were poor. These findings indicate that mDIrot at P wave that related to atrial load, proved to be a good indicator of fetal prognosis.

P wave - atrial load - magnetocardiography