Premature Atrial Contractions in Fetus

Premature atrial contractions in the fetus are early atrial beats followed by a pause, and they are the commonest fetal rhythm disturbance in the second and third trimesters. They are benign and usually resolve before birth. A few progress to supraventricular tachycardia, especially when beats are blocked or come in runs, so surveillance is needed.

• Risk factors: caffeine, nicotine, maternal stimulants, maternal thyroid disease, atrial septal aneurysm.
• Blocked beats may give a slow or irregular rate on auscultation.
• Most babies are born with a normal rhythm.

Women have no symptoms. An irregular heart rhythm with pauses is found on auscultation, Doppler or cardiotocography, with an otherwise normal examination.

• Skipped or pausing beats on auscultation.
• No signs of heart failure or hydrops.
• Differential diagnosis: premature ventricular contractions, blocked atrial bigeminy, supraventricular tachycardia, second degree heart block, normal variation.
• Complications: progression to supraventricular tachycardia in a few, hydrops if tachycardia is sustained, parental anxiety.

The approach is rhythm analysis with a heart scan to exclude structural disease.

• M mode or pulsed Doppler: atrial contraction earlier than expected, ventricular response conducted or blocked; frequency counted over several minutes.
• Fetal echocardiography for structure and function when ectopy is frequent, persistent or runs of more than 2 beats are found.
• Maternal history of caffeine intake in mg daily, drugs, nicotine; TSH and free T4, random glucose, electrolytes.
• Cardiotocography shows isolated irregular tracing and excludes sustained tachycardia.

The principle is reassurance, removal of triggers and surveillance until the rhythm settles.

• Supportive: stop caffeine (tea, coffee, cola, energy drinks), nicotine, alcohol and decongestants; reassure that most settle by term; fetal heart rate check weekly until normal, then at each visit; daily fetal movement counts; delivery as obstetric indications decide.
• Pharmacological: none needed for isolated ectopy; if sustained tachycardia develops give digoxin 0.5 mg oral 8-hourly for 3 doses then 0.25 mg oral 12-hourly, aiming for a maternal serum level of 1.0 to 2.0 nanograms/mL.
• Procedures: fetal echocardiography if beats persist beyond 2 weeks or if tachycardia develops; none otherwise.
• Red flags: sustained rate above 180 beats per minute, hydrops, ascites, reduced fetal movements, frequent runs of beats.
• Follow-up: rhythm check weekly for 4 weeks then at each visit; echocardiography if persistent at 34 weeks; newborn heart rhythm check at birth and ECG if the rhythm is still irregular at 24 hours.