Fetal arrhythmias: Current evidence of prenatal diagnosis and management

Fetal arrhythmias present as an irregular cardiac rhythm and heart rate. Fetal echocardiography and cardiotocography play a pivotal role in diagnosing and managing fetal arrhythmia. Fetal magnetocardiography and electrocardiography can provide electrical assessment but have several limitations; thus, prenatal diagnosis of fetal arrhythmia remains challenging. Most cases of fetal arrhythmia have a structurally normal heart with isolated premature contractions that spontaneously resolve in utero or after birth without treatment. Despite the theoretical advantage of fetoplacental circulation, progression to heart failure or hydrops is found in fetuses with tachy- or bradyarrhythmia due to the limited heart rate reserve. There is a clear clinical consensus on the efficacy of transplacental antiarrhythmic therapy using digoxin, sotalol, and flecainide for fetal supraventricular tachyarrhythmia. A recent Japanese multicenter clinical trial confirmed the efficacy and safety of these agents. Fetal ventricular tachycardia is an infrequent occurrence but can be associated with heart failure, hydrops, and sudden death. It is important to search for long QT syndrome. Transplacental administration of magnesium, propranolol, mexiletine, and lidocaine, alone or in combination, has been attempted for fetal ventricular tachycardia. Fetal complete atrioventricular block is caused by maternal autoantibodies or fetal congenital heart defects and is irreversible. There is currently no consensus on the indications for fetal treatment, including beta-sympathomimetics for bradyarrhythmia. Dexamethasone and intravenous immunoglobulin have been used to prevent or treat atrioventricular block and myocarditis, but recent studies have not shown the efficacy of these agents.