Fetal tachyarrhythmia

Fetal tachyarrhythmia refers to an irregular increase in fetal heart rate. 

Epidemiology

Depending on its exact definition, the prevalance rate is thought to be around 0.5-1% of pregnancies. 

Clinical presentation

Many cases tend to be discovered in the 3^rd trimester. 

Pathology

Sub types

Fetal tachyarrhythmias can be of many types and includes:

• fetal sinus tachycardia: some authors classify this under fetal tachyarrythmias although it probably shouldn't as the rhythm is regular
• fetal supraventricular tachycardia (SVT)
  • most common fetal tachyarrhythmia: accounts for 60-90% of cases
  • has a typical ventricular rate of ~230-280 beats per minute (bpm) ⁴
  • often associated with an accessory AV conduction pathway
• fetal atrial flutter
  • second most common fetal tachyarrhythmia ⁷: can account for up to 25% of cases 
  • has a typical atrial rate of 300-600 bpm
  • often has a variable ventricular rate due to the frequent presence of an AV conduction block
• fetal atrial fibrillation
• fetal ventricular tachycardia 
  • the ventricular rate can be faster than the atrial rate

Associations

• associated congenital cardiac anomalies can occur but are relatively rare ( ~7% ⁷)

Radiographic assessment

Antenatal ultrasound

Evaluation of a tachyarrythmia requires M mode Dopplers which allows correct recognition of the rhythm pattern. Ideally both and ventricle should be included in the scanning field. Assessment for the presence of congenital cardiac anomalies and for complications such has hydrops fetalis are recommoneded as part of routine sonographic assessment. 

Secondary effects of fetal circulation can be additionally assessed by:

• ductus venosus flow assessment
• umbilical vein flow assessment

Complications

• development of hydrops fetalis

Treatment and prognosis

Prognosis is somewhat dependent on the presence of hydrops. As a group, most fetuses (particualrly non hydropic fetuses) do generally well ⁶. A range of anti arrhythmic-arrhythmic agents may be used depending on the exact situation ^ref. 

See also

• fetal tachycardia