Fetal Tachyarrhythmia - Part I: Diagnosis

Fetal tachycardia, first recognized in 1930 by Hyman et al1, is a condition occurring in approximately 0.4-0.6% of all pregnancies2. A subset of these cases with more sustained periods of tachycardia is clinically relevant. The necessity of therapeutic intervention in this condition is still a matter of discussion focused on the natural history of the disease. The spectrum of opinions varies from non-intervention3,4,5 based on a number of cases in which the tachycardia subsided spontaneously6, to aggressive pharmacotherapeutic intervention7,8 based on reports of deterioration of the fetal condition ultimately ending in significant neurological morbidity9,10,11, or fetal demise12,13,14. Prenatal treatment through indirect, maternally administered drug therapy seems to be the preference of most centers15,16,17,18,19,20,21. This matter will be discussed further in Fetal Tachyarrhythmia, Part II, Treatment. The choice of the specific pharmacotherapeutic agents and the chances on success of therapy depend largely on the type of tachycardia. The determination of the type of tachycardia is therefore of the utmost importance20,22, however the available diagnostic armamentarium is limited. The most widely used method of diagnosis of fetal tachycardia, M-mode echocardiography, provides a time related documentation of function of the various cardiac structures. The current subdivision into supraventricular tachycardia (SVT), atrial flutter (AF) and ventricular tachycardia (VT) derived from M-mode echocardiography is not sufficient enough for differentiation according to the electrophysiologic mechanism. Several attempts have been made in the last years to increase the accuracy and reliability of M-mode echocardiography by measurement of atrioventricular (AV) and ventriculoatrial (VA) intervals23,24, and the addition of Doppler echocardiography25,26. New methods registering the actual electrophysiologic events are in development including noninvasive techniques such as magnetocardiography(MCG)27. Characteristics of the most common types of fetal tachycardia are described and examples of M-mode echocardiography and FMCG are presented.