Magnetocardiography in the diagnosis of fetal arrhythmias

Abstract

In 1899, Wenckebach described the phenomenon that bears his name. His initial observation was in a 40-year-old patient “with nervous temperament” who had an irregular pulse, in whom he worked out the mathematical relationship between atrial and ventricular activity. Often forgotten is the fact that Wenckebach accomplished this feat before the advent of clinical electrocardiography. While electrocardiographic tracings were recorded with Gabriel Lippmann’s capillary electrometer, for example, by Waller, it was Einthoven’s sentinel publication of the development of the galvanometer for the recording of the electrocardiogram in humans in 1902 that led to the adoption of electrocardiography in clinical studies. Wenckebach used carotid and jugular venous pulse tracings in his patient and went on to further study the phenomenon in frog suspended heart preparations. His methods, therefore, relied entirely on mechanical cardiac events, from which he hypothesized electrical events, interestingly, before the anatomic description of the atrioventricular (AV) node. Today’s fetal cardiologists are, for the most part in the same boat with Einthoven, forced to deduce electrical events in the fetal heart from recordings of mechanical events (via M-mode and Doppler tracings). Attempts at recording a standard electrocardiogram by the use of electrodes placed on the mother’s abdomen have not been reliably successful, likely owing to a low signal-to-noise ratio, exacerbated in late gestation by fetal vernix caseosa, which acts as an insulator. Thus, most fetal cardiologists are unable to observe characteristics that electrocardiographers rely on routinely, such as QRS duration, preexcitation, QRS axis, and P-wave morphology, as well as critical findings such as QT interval prolongation and T-wave alternans. Enter the magnetocardiogram (MCG). It is beyond the scope of this commentary to fully describe this technology. However, the technique records the changes in the electrical fields that are generated by cardiac electrical activity, producing a higher signal-to-noise ratio, through the use of a sensitive recording device. It is feasible for use in recording fetal cardiac electrical activity. This methodology is currently limited to a few centers worldwide.