This study was to review experience and outcomes of supraventricular (SV) arrhythmias in fetus Methods: Cases were divided in groups: SVPB= premature SV beats, NSSVT= non-sustained SV tachycardia, SSVT= sustained SV tachycardia, and AF= atrial flutter. Heart failure (HF) was defined as foetal hydrops or isolated effusion (pericardial or pleural or ascitis). Outcome was favourable if arrhythmia resolved or stabilized until full-term birth, not-favourable if premature birth or foetal death occurred.

188 fetuses were included:89 in SVPB(47.3%), 31 in NSSVT(16.5%), 60 in SSVT(31.9%), 8 in AF(4.3%), aged at diagnosis 30.8±4.5weeks (no difference between groups). Foetus HR at diagnosis was 241±30bpm in SSVT vs 226±26 in AF. Antiarrhytmic therapy was administered in sustained tachycardia (83% of SSVT and 71% AF): 28 had 1 medication, 25: 2 medications, 2: 3 medications. Complication occurred in 29 cases, all in SSVT and AF (29 of 68= 43%): 18 hydrops, 5 ascitis, 4 pericarditis, 1 pleural effusion and 1 LVdysfunction+MR, was more frequent in SSVT (86%: hydrops in 30%) than AF (51%: no hydrops), p= 0.08. Fetal HF was associated with HR at diagnosis: 251±25bpm in hydrops vs 228±31bpm in nohydrops (p=0.025). Outcome was favourable in SVPB and NSSVT, in 45 of SSVT+AF (79%). Tachycardia resolved in 36, more frequently in SSVT (57%) than AF (25%). HR only decreased in 9cases. Premature birth occurred in 10, foetal death in 2. Outcome was not associated with HR or weeks of gestation at diagnosis. Defavourable outcome was more frequent in hydrops or isolated effusion (57%) than in uncomplicated cases (10%, p= 0.0002). Resolution occurred in 45% hydrops vs 66% of non-hydrops cases. Digoxine decreased from 79% of cases before 2000 to 33% after 2000, while flecaine increased from 14% to 48.5%. There was no relationship between therapy or number of medications and outcomes.

Fetal SSVT more frequently resolves but has worse outcome than AF, especially if HR at diagnosis is high and hydrops occurs. Larger scale prospective studies are needed to evaluate the efficacy of flecaine compared to digoxine therapy.