ABC | Volume 112, Nº5, May 2019

Guideline Brazilian Fetal Cardiology Guidelines – 2019 Arq Bras Cardiol. 2019; 112(5):600-648 Figure 7.2 – Suggested approach for fetuses who have CAVB. CAVB: complete atrioventricular block; HR: heart rate. FETAL CAVB Diagnosis of CAVB Anti-SSA/RO antibodies Consider dexamethasone HR > 55 bpm HR < 55 bpm No additional medication ß2 stimulation with sympathomimetic drugs (IIa/C) Other intermittent tachycardias usually do not have signs of cardiac hemodynamic impairment, and there is no indication for treatment. 171 However, in isolated cases, it may evolve to sustained tachycardia, justifying its follow up. 7.4.2. Sustained Tachycardias This group of fetal arrhythmias, identified by a period of more than 50% of exam duration, includes supraventricular tachycardias, AF, and ventricular tachycardias. The therapeutic goal is to bring the gestation to term, while improving secondary manifestations. Prognosis is good when they are reversed in utero and limited for immature fetuses with hydrops and cases of arrhythmia which were not successfully reversed. Prognosis should be considered favorable when fetuses continue with tachyarrhythmia, but with lower heart rates and improvement in hydrops. 7.4.2.1. Diagnosis Sustained atrial tachycardia is characterized by a cardiac rhythm with 1:1 A:V conduction and heart rate above 180 bpm, usually above 220 bpm. 17,137,138,141 It is important to understand the underlying mechanism of the arrhythmia, assessing simultaneously the atrial and ventricular activity. Using Doppler flow tracing, it is possible to measure the AV (atrium → ventricle) and VA (ventricle < atrium) intervals, which correspond, analogously and respectively, to PR and RP intervals in an electrocardiogram. When the VA interval is greater than the AV, the most possible diagnosis is reentrant tachycardia (95%); when the VA interval is greater 630