Fetal magnetocardiogram waveform characteristics

Abstract

Background: Fetal magnetocardiography (fMCG) is the most direct and precise method of assessing fetal rhythm and conduction. Although the utility of fMCG for evaluation of fetuses with serious arrhythmia is generally acknowledged, many aspects fetal rhythm and conduction are relatively unstudied.Objective: To record fMCG in a large group of normal fetuses in order to provide a more comprehensive evaluation of fMCG waveform characteristics, including waveform intervals, amplitudes, and morphology. Approach:The subjects were 132 healthy women with uncomplicated singleton pregnancies, studied at 15.7-39.9 (mean 28.9) weeks' gestation in 259 sessions. The P, PR, QRS, QT, QTc, and RR intervals and the P/QRS and T/QRS amplitude ratios were measured.Main Results: The P, PR, QRS, and RR intervals increased with gestational age, but QT and QTc did not. U-waves were seen in 11% of fetuses. The T-waves were often flat with low T/QRS amplitude ratios. Equiphasic QRS complexes were associated with tall P-waves. The PR, QRS, and QT intervals showed a power law dependence on RR interval with power law exponents 0.445, 0.363, and 0.381, respectively. Significance:The data establish prediction intervals for fMCG waveform intervals and amplitudes in normal fetuses. This is critical for identification of fetuses with abnormal rhythm. Our study is the first to document the incidence of U-waves and flat T-waves in the fetus, both of which are uncommon postnatally. The association of tall P-waves with equiphasic QRS complexes provides a useful means of improving the resolution of fetal P-waves.

Fetal diagnosis of KCNQ1‐variant long QT syndrome using fetal echocardiography and magnetocardiography

“…No obvious ventricular arrhythmias were noted. The mean normal QTc interval by fMCG at 15‐24 weeks gestation is reported to be 398.4 ± 50.1 msec 4 . Given the fMCG findings and autosomal‐dominant transmission of LQTS, the mother was transitioned to nonsustained release propranolol of 60 mg every 8 h and subsequently 80 mg every 8 h for a more reliable presumed effect of the drug on fetal rhythm.…”

“…If the heart rate did not fall below what was already seen in the fetus, it was felt conduction disease had not worsened, and the likelihood of hydrops was low. The upper rate limit was chosen based on reported normal fetal heart rates to avoid missing torsades de pointes 3,4 . The mother did not call about abnormal fetal Dopplers.…”

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

“…It is important to note that detection of biomagnetic signals gives the possibility of obtaining reference-free and coherent measurements that do not depend on the dielectric properties of biological systems. For example, magnetocardiography gives the possibility of obtaining earlier information about cardiac conduction abnormalities in the fetal period of human development [3]. This can lead to a clinical decision for medical intervention, even before birth [4].…”

“…Panel (a) shows a mechanical resonator consisting of a magnetostrictive material (1) and moving mirror (2) bonded to the Fabry-Pérot optical resonator consisting of a fixed mirror (3), optical path length (4), light emitter (5), and detecting system(6). Panel (b) schematically represents the sensing element of the magnetometer including an optical fiber (1), resonator system (2), and magnetostrictive material(3) which is sensitive to the applied external magnetic field H ext .…”

“…Schematic image of the sensing element of the spin wave-based magnetic field sensor consisting of a spin waves generator (1) exciting spin waves in two antennas (2) detected by the spin wave detector(3), where H ext and H bias are the applied out-of-plane and bias in-plane external magnetic fields, respectively.…”