ABC | Volume 112, Nº5, May 2019

Guideline Brazilian Fetal Cardiology Guidelines – 2019 Arq Bras Cardiol. 2019; 112(5):600-648 compression by the transducer. It also may occur due to maternal illnesses. When transitory, they are commonly benign and do not require treatment. However, persistent bradycardia indicates fetal abnormality and its causes should be treated. 48,129,134,137,141 7.3.2. Low Atrial Rhythm The main mechanisms of low atrial rhythm include congenital displacement of atrial activation, acquired damage of the sinoatrial node, channelopathy, and secondary suppression of sinus node rate. Left and right atrial isomerism can occur, with fetal heart rate varying from 80 to 130 bpm. Situations that may cause sinus node fibrosis, such as maternal anti-Ro/ anti-LA antibodies or viral myocarditis, may occur with progression to fetal death. Additionally, maternal use of medications, such as sedatives or betablockers, may reduce the sinus node rate. Low atrial rhythm does not require treatment. 137 7.3.3. Blocked Atrial Bigeminy Blocked atrial bigeminy occur with a heart rate ranging from 75 to110 bpm in a 2:1 atrioventricular conduction. They do not require treatment. It is known, however, that approximately 10–13% may evolve to SVT; weekly evaluation of fetal heartbeats is thus recommended by echocardiogram or sonar. 137,142 7.3.4. Complete Atrioventricular Block CAVB results in complete dissociation between atrial and ventricular activity, with heart rates usually below 60 bpm. In 50–55% of cases, malformation of the conduction system occurs, as a consequence of structural heart diseases, such as congenitally corrected transposition of great arteries and left atrial isomerism. 141,143-146 In about 40% of the cases, it occurs due to maternal autoimmune diseases that present with anti-SSA/SSB (anti-Ro/LA antibodies). 142-147 The risk increases in the presence of anti-Ro 52-kd (sequence p200) antibodies, that cannot be tested in Brazil yet. 147-153 In a minority of cases, no etiology is identified. Fetuses without hydrops and with heart rate above 55 bpm have good prognoses. In immature fetuses, with very early hydrops and heart rates below 50 bpm, prognosis is more limited. Fetuses with CAVB and structural heart diseases, such as left atrial isomerism, have a poor prognoses. 145 In mothers with autoimmune diseases, it is recommended to test maternal anti-SSA/RO antibodies. If positive, and the fetus is in sinus heart rhythm, weekly measurements of the AV interval (mechanical PR interval) are recommended, from weeks 18 to 26. This measurement should be taken employing pulsed- wave Doppler, evaluating mitral and aortic flows simultaneously, from the beginning of the mitral A wave (“A”) to the beginning of the ventricular systole (“V”). 142 Myocardial function should be monitored every 4 weeks up to delivery (grade of recommendation: I; level of evidence: C) (Figure 7.1). 154 A l t hou g h c on t r o v e r s i a l , t r e a tmen t w i t h dexamethasone at a dose of 4–8 mg orally can be started to cases where the AV interval is > 150 milliseconds or when it increases progressively. Some groups have shown to be beneficial the treatment of immune CAVB with maternal dexamethasone (4–8 mg orally) and/or intravenous gammaglobulin infusion, 149-158 observing reduced inflammatory response, stabilization of first- and second-degree AVB, regression of endocardial fibroelastosis and hydrops improvement. 145-151 However, the use of corticosteroids may be associated with complications, such as ductal constriction, maternal diabetes, restricted growth, and oligohydramnios. 149-161 Dexamethasone may be used to treat first- and second-degree AVB associated with signs of myocardial inflammation (myocardial hyperechogenicity, valve regurgitation, cardiac dysfunction, and pericardial effusion) to prevent progressing to CAVB, however the efficiency of corticosteroids has not been completely established and one may consider its possible side effects. 140 In fetuses with CAVB without functional consequences, dexamethasone may also be used to reduce the prevalence of dilated cardiomyopathy. 152,162 Whenever significant side effects occur in the mother or the fetus, the use of the medication should be interrupted. Intravenous immunoglobulin associated with dexamethasone may improve survival in fetuses with endocardial fibroelastosis or systolic dysfunction. 149 It is not yet known, however, when is the ideal moment for administration and the ideal intervals between doses. There is no recommendation regarding the prophylactic use of immunoglobulin at the beginning of gestation for mothers with positive antibodies. 160 The use of salbutamol, terbutaline, or isoprenaline is indicated when heart rate is < 55 bpm and/or in the presence of fetal heart failure and hydrops. 142,146,157 These medications are usually well tolerated. Maternal extrasystole and sinus tachycardia may appear. 161 There is an increase in fetal heart rate of approximately 10 to 15% of the basal frequency, and, although small, it may prolong the gestation to or close to term. There are no studies demonstrating that these medications modify fetal survival in these cases. In immature fetuses with hydrops, with very low heart rate, in utero implantation of a pacemaker may be considered. This procedure 628