Diagnosis and treatment of fetal arrhythmia

Abstract

Aims: Detection and careful stratification of fetal heart rate (FHR) is extremely important in all pregnancies. The most lethal cardiac rhythm disturbances occur during apparently normal pregnancies where FHR and rhythm are regular and within normal or low-normal ranges. These hidden depolarization and repolarization abnormalities, associated with genetic ion channelopathies cannot be detected by echocardiography, and may be responsible for up to 10% of unexplained fetal demise, prompting a need for newer and better fetal diagnostic techniques. Other manifest fetal arrhythmias such as premature beats, tachycardia, and bradycardia are commonly recognized.

Methods: Heart rhythm diagnosis in obstetrical practice is usually made by M-mode and pulsed Doppler fetal echocardiography, but not all fetal cardiac time intervals are captured by echocardiographic methods.

Results and conclusions: This article reviews different types of fetal arrhythmias, their presentation and treatment strategies, and gives an overview of the present and future diagnostic techniques.

Fig. 1

A 20-second signal-averaged waveform of a normal fetal heart rate in a 38-week gestational age fetus by (a) fECG and (b) fMCG. fECG, fetal electrocardiogram; fMCG, fetal magnetocardiography.

Fig. 2

Dr. Strasburger performing ultrasound within the magnetically shielded room at UW-Madison Biomagnetism Laboratory, The superconducting quantum interference device above the patient is not yet in position against the maternal abdomen.

Fig. 3

Ventricular ectopy in a bigeminy pattern.

Fig. 4

AV block by (a) echocardiography and (b) fMCG. AV, atrioventricular; fMCG, fetal magnetocardiography.

Fig. 5

SVT measured by (a) echocardiography and (b) by fMCG. fMCG, fetal magnetocardiography; SVT, supraventricular tachycardia.

Fig. 6

(A) Fetal heart rates (FHRs) in group 1 with long QT syndrome were substantially lower than group 2 without long QT syndrome (used with permission from Cuneo et al). Only five FHRs in group 1 were below 110 bpm, the usual cutoff for defining fetal bradycardia. But when the predicted minimum FHR for gestational age was used as a reference, all except three were low. Thus fetuses are at risk for underdetection of LQTS when FHRs fall between 110 bpm and the low-normal range of approximately 120 to 135 bpm. Not all fetuses with FHRs in this range, however, have LQTS. (B) Signal-averaged complex showing cardiac time intervals in a fetus with long QT syndrome. QTc is 625 ms using Bazett formula, FHR 131 bpm sinus rhythm, T-wave alternans can be seen.