case_images: PMC11303133_01
case_images: Fetal echocardiogram (2D image with color Doppler and flow Doppler) at 19 weeks of gestation, showing a prolongation of mechanical PR interval. On the top right corner of the image are presented the different measurements: 150, 157, 147, 150, 150 milliseconds.
case_images: fimmu-15-1397103-g001.jpg
case_images: PMC11303133_01_fimmu-15-1397103-g001.jpg
case_images: f1
case_images: Two consecutive fetal echocardiograms revealed a prolonged mechanical PR interval (150-157 msec), suggestive of a first-degree AVB ( Figure 1 ), with no structural or functional heart disease.
case_images: Fetal echocardiogram (Flow Doppler) at 21 weeks of gestation, revealing fetal supraventricular tachycardia alternating with sinus rhythm (a more explicit video is presented in 
  Supplementary Material
  ).
case_images: fimmu-15-1397103-g002.jpg
case_images: PMC11303133_01_fimmu-15-1397103-g002.jpg
case_images: f2
case_images: At 21 WG, a fetal echocardiogram revealed short periods of paroxysmal supraventricular tachycardia (fetal heart rate 260 bpm; normal PR interval 124-129 msec) ( Figure 2 ).
case_images: PMC11303133_02
case_images: Holter of the newborn at 1 month-old. It. It is noticeable a short PR interval and a slurred QRS complex (delta wave) compatible with a Wolf-Parkinson-White Syndrome.
case_images: fimmu-15-1397103-g003.jpg
case_images: PMC11303133_02_fimmu-15-1397103-g003.jpg
case_images: f3
case_images: At 1 month-old, a Holter monitoring revealed a short PR interval and a slurred QRS complex, consistent with WPWS ( Figure 3 ).
case_images: PMC11303133_03
case_images: Timeline of events, from the beginning of pregnancy until the postpartum period. In X axis, the weeks of gestation. In Y axis, units of anti-SSA/Ro antibodies (at 9 WG, in UQ; from 19 WG on in FLU units). The blue line represents the Ro52 levels and the orange line represents the Ro60 levels. PP, postpartum
  First degree AV block
  Sinus rhythm
  Supraventricular tachycardia
  Intravenous immunoglobulin
  Dexamethasone
  Flecainide
case_images: fimmu-15-1397103-g004.jpg
case_images: PMC11303133_03_fimmu-15-1397103-g004.jpg
case_images: f4
case_images: Regular follow-up appointments with pediatric cardiology are ongoing, and no new episodes of rhythm alteration were identified so far.  Figure 4  illustrates the timeline of events, from the beginning of pregnancy until the postpartum period.