Fetal dysrhythmias : Practice points


Fetal cardiac dysrhythmias are potentially life-threatening conditions. However, intermittent
extrasystoles, which are frequently encountered in clinical practice, do not require treatment.
Sustained forms of brady- and tachyarrhythmias might require fetal intervention. Fetal echocardiography
is essential not only to establish the diagnosis but also to monitor fetal response to therapy.
In the last decade, improvements in ultrasound methodology and new diagnostic tools have
contributed to better diagnostic accuracy and to a greater understanding of the electrophysiological
mechanisms involved in fetal cardiac dysrhythmias.

Practice Points

  • Rhythm disturbances are diagnosed in at least 2% of pregnancies during routine
    scanning.
  • Most fetal dysrhythmias are intermittent extrasystoles that have little clinical
    relevance and require no treatment.
  • Less than 10% of referrals have prolonged or persistent tachy- or bradyarrhythmias
    that require therapy.
  • Persistent tachycardia and heart block are associated with increased fetal and
    perinatal mortality, requiring close fetal surveillance.
  • Fetal echocardiography allows correct diagnosis of the dysrhythmia, its underlying
    mechanism and exclusion of structural abnormalities.
  • Prognosis is governed by the type of arrhythmia, the association with structural
    cardiac anomaly and the co-existence of intrauterine cardiac failure.
  • Presence or absence of hydrops fetalis is the most important factor in determining
    the outcome of tachyarrhythmias and heart block.
  • The most common types of tachyarrhythmia are re-entry supraventricular
    tachycardia and atrial flutter.
  • Persistent fetal tachycardias should be treated promptly with anti-arrhythmic
    drugs given either transplacentally or via direct fetal route.
  • Well-tolerated and relatively safe anti-arrhythmic drugs are available for the
    successful treatment of fetal tachycardias.
  • Second- and third-degree (complete) AV block should be distinguished from
    blocked atrial bigeminy as management and prognosis differ.
  • The treatment of fetuses with immune-mediated heart block with steroids
    remains debatable.

Research in progress

  • Efficacy of preventive treatment to influence progression of immune-mediated
    atrioventricular block.
  • Efficacy of transplacental treatment (steroids, b-agonists) for immune-mediated
    complete heart block.
  • Controlled trials on efficacy and on the maternal and fetal safety of drugs used
    to treat fetal tachycardia.
  • Investigation of potential long-term effects of prolonged in-utero exposure to
    high-dose steroids used to treat heart block.
  • Long-term neurodevelopmental outcome of fetal hydrops associated with lifetheatening
    dysrhythmias.
  • Further development of transabdominal ECG, transesophageal ECG and MGC.
  • Direct fetal cardiac pacing.

FROM : Olus Api and Julene S. Carvalho : Fetal dysrhythmias: Best Practice & Research Clinical Obstetrics and Gynaecology
Vol. 22, No. 1, pp. 31–48, 2008

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