![]() In utero 2nd degree AV block with or without intermittent Torsades de pointes (TdP) can be attributed to LQTS. The fetus with repeated heart rates of less than third percentile of gestational age may have Long QT Syndrome (LQTS). The recurrence rate of CHB is at least two to three times higher than that of the first affected pregnancy, supporting the need for close echocardiographic monitoring in all subsequent pregnancies, with heightened surveillance between 18 and 24 weeks of gestation. Autoantibody-associated CHB is not coincident with major structural abnormalities, is most often identified in the late second trimester, carries a higher mortality, and frequently requires a pacemaker in the neonatal period. The presence of maternal anti SS-A/Ro or anti SS-B/La antibodies has been associated with an increased risk for fetal CHB. There is a high association of isolated CHB with maternal lupus, and all gravid mothers with fetal CHB should undergo testing for autoantibodies. Isolated CHB in the absence of structural heart disease is usually well tolerated in utero and does not lead to hemodynamic consequences unless the heart rates are consistently less than 60 beats per minute. The combination of CHB and structural heart disease is usually an ominous sign with a high likelihood of hydrops leading to fetal or neonatal death. In patients presenting with fetal CHB, complex structural heart defects have been reported in up to 53% of the patients. The incidence of CHB at birth has been reported to be approximately 1 in 20,000. Sustained fetal bradycardia is most commonly secondary to congenital CHB. Sinus bradycardia per se is well tolerated but may be secondary to fetal distress, sinus node dysfunction (anti-Ro antibody related, left isomerism), and LQTS (KCNQ1 mutations). įetal bradycardia that is non-sustained may be secondary to an exaggerated variability of the sinus rhythm. The combination of a sustained arrhythmia, structural heart disease and hydrops fetalis is an ominous sign carrying a poor prognosis. Both fetal brady and tachyarrhythmias can be associated with structural heart disease and warrant a thorough echocardiogram and evaluation by a pediatric cardiologist. Fetuses of mothers suffering from a connective tissue disease (commonly Sjogren's syndrome or Systemic Lupus Erythematosus) are at risk for developing isolated complete heart block. In fetuses with bradycardia, a slow ventricular escape rate of less than 55 beats/minute appears to be poor prognostic factor. Earlier onset in gestation of a tachyarrhythmia and a higher ventricular rate are other risk factors associated with a greater risk for development of hydrops fetalis. Hence, patients with hydrops and a normal heart rate warrant repeat assessment of the fetal heart rate to detect intermittent arrhythmias. Intermittent tachycardias can also be associated with hydrops. If the arrhythmia is sustained, there is a greater risk of fetal hemodynamic compromise leading to hydrops fetalis and fetal demise. ![]() įetal arrhythmias are usually detected during routine auscultation of the fetal heart or during an obstetric scan. ![]() In approximately 10% of pregnancies complicated by fetal arrhythmias, the arrhythmia may be life-threatening. Fetal arrhythmias can be detected in approximately 1% of all fetuses and up to 49% of all referrals for fetal echocardiography. Other arrhythmias include tachyarrhythmias (heart rate in excess of 160 beats/min) such as atrioventricular (AV) reentry tachycardia, atrial flutter, and ventricular tachycardia, and bradyarrhythmias (heart rate <110 beats/min) such as sinus node dysfunction, complete heart block (CHB) and long QT syndrome (which is associated with sinus bradycardia and pseudo-heart block). Most of the fetal rhythm disturbances are the result of premature atrial contractions (PACs) and are of little clinical significance. The rate, duration, and origin of the rhythm and degree of irregularity usually determine the potential for hemodynamic consequences. A fetal heart rate is considered abnormal if the heart rate is beyond the normal ranges or the rhythm is irregular. The normal fetal heart rate ranges between 110 and 160 beats per minute.
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