Abnormalities of the fetal heart rhythm: irregular rhythm and the most common fetal tachyarrhythmias

Abnormalities of the rhythm and conduction of the fetal heart are detected quite rarely, namely, in 1–5% of pregnancies, according to various authors. In more than 90% of cases, arrhythmias are short-term and single episodes that have little clinical significance. However, about 10% of all arrhythmias are potentially life-threatening to the fetus. The mechanisms of heart rhythm disorders can be divided into abnormalities in the generation and abnormalities in the electrical impulse conduction. Rhythm disorders caused by the SA node refer to arrhythmias when the sinus node operate at an unusually fast or slow speed, that is, sinus tachy- or bradyarrhythmias. Ectopic heart rhythms (extrasystoles) occur when the pacer shifts from the SA node to the latent pacer. Abnormal pulse propagation is the circular propagation of an impulse around additional pathways – re-entry (supraventricular tachycardia, atrial flutter) or a disorder in the conduction of the pulse through the conduction system of the heart (AV block). Fetal arrhythmias usually refer to an irregular rhythm with a normal fetal heart rate (HR), tachyarrhythmia, defined as heart rate >180 beats/min, and bradyarrhythmia, defined as heart rate<110 beats/min. Fetal tachyarrhythmias can be divided into sinus tachycardia, supraventricular tachycardia, ventricular tachycardia. Many cases of abnormal fetal heart rhythm are of minor clinical significance, however, prolonged tachyarrhythmias or arrhythmias with ventricular heart rate of more than 200 beats per minute often cause heart failure and hydrops fetalis.

Conclusion: Fetal arrhythmias are serious conditions that require treatment to prevent heart failure and fetal death. It is necessary to perform ultrasound examination of the fetal heart to understand the main mechanism of rhythm disorders, to study the effect of arrhythmia on cardiac function, as well as to monitor the condition of the fetus during antiarrhythmic treatment.