Usefulness of magnetocardiography for the investigation of fetal arrhythmias

The electrical excitation of the heart causes weak magnetic fields that can be recorded without skin contact over the body surface. Cardiac magnetic activity measures in the range of 0.2 to 5 picotesla (pT) in fetuses and 50 pT in adults, thus approximately 1 million times weaker than the static magnetic field of the earth. Therefore, it was not until the introduction of highly sensitive Superconducting Quantum Interference Device detectors and multichannel equipment that sensitive and low-noise registrations of cardiac magnetic fields became feasible in clinical practice. In 1974, the first fetal “magnetocardiogram” was published by Kariniemi and coworkers 1 ; later studies demonstrated the ability of magnetocardiography (MCG) to detect noninvasively fetal cardiac activity with high resolution and success rates from the second trimester onward. 2‐ 4 MCG provides information equivalent to the surface electrocardiogram (ECG), which is obviously unsuccessful in fetuses. Especially in late pregnancy, the signal of the fetal ECG is severely attenuated due to the insulating properties of the vernix caseosa and volume conduction effects. 5 Although Doppler echocardiography constitutes the gold standard for the analysis of fetal arrhythmias, MCG offers insights into electrophysiologic features of prenatal arrhythmias. An increasing number of recent publications emphasize interest in this field. 6‐ 9 In the present study, we investigated the feasibility of MCG in a clinical work routine to