Standardization of the PQRST waveform and analysis of arrhythmias in the fetus using vector magnetocardiography

Fetal magnetocardiography (fMCG) is useful for analysis of fetal cardiac events. However, fetal presentation and movement affect the fMCG waveform, making it difficult to standardize the waveform. The aim of this study was to investigate whether the use of vector magnetometers can compensate for these limitations. We studied 59 fetuses (gestational age, 22-40 wk, median, 32), including 41 with uncomplicated pregnancies and 18 with fetal cardiac disease. fMCG was recorded twice in each case, and the two waveforms were compared with each other in uncomplicated subjects to investigate the effects of fetal presentation. The superconducting quantum interference device (SQUID) system used in this study was a 12-channel vector magnetometer, by which the three components of the magnetic field (Bx, By, Bz) could be detected simultaneously at four recording points. By constructing the three components, a composite waveform (Bxyz) was obtained. The configuration of the composite waveforms was similar among normal fetuses always with positive polarity, independent of fetal presentation and movement. The difference in the time intervals (PR, QRS, and ventricular activation time [VAT]) between the first and second measurements was minimal in the composite waveforms (Bxyz) compared with that in each channel (Bx, By, Bz). Even before signal averaging, waveforms with high time resolution were recorded in at least one of the three components, making it possible to analyze fetal arrhythmias precisely. Our results indicate that vector magnetocardiography is potentially useful for standardization of the fMCG waveforms and to provide a more complete and accurate analysis of fetal arrhythmias.