Contribution of Fetal Magnetocardiography to Diagnosis, Risk Assessment, and Treatment of Fetal Arrhythmia.

Background Fetal echocardiography has been the mainstay of fetal arrhythmia diagnosis; however, fetal magnetocardiography (fMCG) has recently become clinically available. We sought to determine to what extent fMCG contributed to the precision and accuracy of fetal arrhythmia diagnosis and risk assessment, and in turn, how this altered pregnancy management. Methods and Results We reviewed fMCG tracings and medical records of 215 pregnancies referred to the Biomagnetism Laboratory, UW-Madison, over the last 10 years, because of fetal arrhythmia or risk of arrhythmia. We compared referral diagnosis and treatment with fMCG diagnosis using a rating scale and restricted our review to the 144 subjects from the tachycardia, bradycardia/AV block, and familial long QT syndrome categories. Additional fMCG findings beyond those of the referring echocardiogram, or an alternative diagnosis were seen in 117/144 (81%), and 81 (56%) were critical changes. Eight (5.5%) had resolution of arrhythmia before fMCG. At least moderate changes in management were seen in 109/144 (76%) fetuses, of which 35/144 (24%) were major. The most diverse fMCG presentation was long QT syndrome, present in all 3 referral categories. Four of 5 stillbirths were seen with long QT syndrome. Nine fetuses showed torsades de pointes ventricular tachycardia, of which only 2 were recognized before fMCG. Conclusions FMCG has a significant impact on prenatal diagnosis and management of arrhythmias or familial arrhythmia risk, which cannot be fully met by existing technology. The combination of fMCG and fetal echocardiography in fetal care centers will be needed in the future to optimize care.

Low-Cost Fetal Magnetocardiography: A Comparison of Superconducting Quantum Interference Device and Optically Pumped Magnetometers.

Background Fetal magnetocardiography (fMCG) is a highly effective technique for evaluation of fetuses with life-threatening arrhythmia, but its dissemination has been constrained by the high cost and complexity of Superconducting Quantum Interference Device (SQUID) instrumentation. Optically pumped magnetometers (OPMs) are a promising new technology that can replace SQUIDs for many applications. This study compares the performance of an fMCG system, utilizing OPMs operating in a person-sized magnetic shield, to that of a conventional fMCG system, utilizing SQUID magnetometers operating in a magnetically shielded room. Methods and Results fMCG recordings were made in 24 subjects using the SQUID system with the mother lying supine in a magnetically shielded room and the OPM system with the mother lying prone in a person-sized, cylindrical shield. Signal-to-noise ratios of the OPM and SQUID recordings were not statistically different and were adequate for diagnostic purposes with both technologies. Although the environmental noise was higher using the small open-ended shield, this was offset by the higher signal amplitude achieved with prone positioning, which reduced the distance between the fetus and sensors and improved patient comfort. In several subjects, fMCG provided a differential diagnosis that was more precise and/or definitive than was possible with echocardiography alone. Conclusions The OPM-based system was portable, improved patient comfort, and performed as well as the SQUID-based system at a small fraction of the cost. Electrophysiological assessment of fetal rhythm is now practical and will have a major impact on management of fetuses with long QT syndrome and other life-threatening arrhythmias.

Assessment of left ventricular pre-ejection period in the fetus using simultaneous magnetocardiography and echocardiography.

INTRODUCTION: Fetal magnetocardiography (fMCG) is a promising new technique for assessing fetal rhythm; however, no prior studies have utilized fMCG to evaluate human fetal electromechanical physiology. Pre-ejection period (PEP) is an important measure of the electromechanical activation of the heart, and is altered by disease states and arrhythmias. MATERIALS AND METHODS: A novel technique was used to assess fetal PEP and its relationship to other fetal systolic time intervals, RR interval, and gestational age (GA). 25 normal human fetuses between 19 and 38 weeks' gestation were studied using simultaneous pulsed Doppler ultrasound and fMCG. Correlations among PEP, ejection time, QRS width and RR interval were assessed using linear regression. RESULTS: Across all subjects, PEP was found to correlate with GA (R = 0.57, p < 0.0001), QRS width (R = 0.35, p = 0.026), and RR interval (R = 0.37, p = 0.018). In individual sessions, PEP negatively correlated beat-to-beat with the preceding RR interval. CONCLUSION: PEP exhibits developmental trends that provide a better understanding of the normal development of the human fetal heart.

Assessment of fetal neurodevelopment via fetal magnetocardiography.

Fetal magnetocardiography (fMCG) offers unique capabilities for assessment of fetal heart rate (FHR) and fetal behavior, which are fundamental aspects of neurodevelopment. The most important attribute of fMCG for FHR monitoring is its high precision, which allows accurate assessment of beat-to-beat fetal heart rate variability (FHRV), including respiratory sinus arrhythmia. Using mathematical indices to assess FHRV, we find that short- and long-term FHRV both increase during gestation but not in the same manner. The largest increases in short-term FHRV occur during the last trimester, while the largest increases in long-term FHRV occur early on, with smaller changes occurring during the last trimester. The fMCG also allows assessment of fetal activity. This results from the high sensitivity of the signal to the position and orientation of the fetal heart. FMCG actograms are therefore specific for fetal trunk movement, which are thought to be more important than isolated extremity movements and other small fetal movements. The ability to assess FHR, FHRV, and fetal trunk movement simultaneously makes fMCG a valuable tool for neurodevelopment research.