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KEY POINTS
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Key Points

  • Fetal tachyarrhythmias include isolated extrasystoles, supraventricular tachycardia, and atrial flutter.

  • Approximately 1% of fetuses are diagnosed with an arrhythmia.

  • Isolated extrasystoles are the most common tachyarrhythmias and are for the most part benign.

  • Supraventricular tachycardia is the most common serious dysrhythmia detected prenatally. The majority are re-entrant and are identified by a fetal heart rate of greater than 200 beats per minute with one-to-one atrial-to-ventricular activity. Congenital heart disease is associated with this arrhythmia 5% to 10% of cases.

  • The rate with atrial flutter is usually between 300 and 500 beats per minute. The ventricular response depends on the degree of atrioventricular block. This dysrhythmia has a poor prognosis due to the fact that it is associated with hydrops and with congenital heart defects.

  • Fetal dysrhythmias have the potential for serious sequelae including fetal hydrops.

  • Fetal arrhythmias are diagnosed by fetal echocardiography that includes M-mode assessment and Doppler analysis. A full anatomical survey including a detailed survey of the fetal heart should also be performed.

  • Although premature atrial and ventricular contractions are considered benign, sustained tachyarrhythmia may develop in up to 1% of fetuses diagnosed with this condition. Thus, serial fetal heart rate auscultation is suggested.

  • Spontaneous resolution of supraventricular tachycardia has been reported.

  • For the most part, fetal supraventricular tachycardia associated with congenital heart defects has been associated with a poor prognosis.

  • Gestational age is an important factor when determining how best to manage a fetal dysrhythmia.

  • Digoxin is the first-line therapy for isolated fetal tachyarrhythmia. Procainamide, flecainide, and sotolol are reserved for second-line treatment.

  • If hydrops is concomittent, the tachyarrhythmia may take longer to resolve.

  • Intermittent fetal tachycardia without evidence of fetal hemodynamic compromise can be observed closely instead of undergoing medical therapy.

  • Refractory cases to maternal medical management have been treated with direct fetal therapy.

  • The newborn should be evaluated thoroughly for signs of cardiac abnormalities. Approximately 50% of infants will relapse after birth.

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CONDITION
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Fetal tachyarrhythmias detected in utero include irregular cardiac rhythm resulting from isolated extrasystoles, supraventricular tachycardia, and atrial flutter. The most common of the above arrhythmias is an irregular cardiac rhythm resulting from isolated extrasystoles (Silverman et al., 1985; Kleinman, 1986; Copel et al., 2000). Most of these extrasystoles originate in the atria and resolve spontaneously (Kleinman, 1986; Reed et al., 1987). An increased frequency of premature beats has been attributed to the maternal use of caffeine, tobacco, and alcohol (De Vore, 1984). Although premature atrial or ventricular contractions have not been considered a risk factor for anomalies in the past, more recent reports suggest that a fetal structural cardiac abnormality may be found in up to 2% of such cases (Beall and Paul, 1986; Reed, 1991).

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Supraventricular tachycardia is the most common serious dysrhythmia detected prenatally (Bergmans et al., 1985; Kleinman et al., 1985a). The majority ...

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