Tiruvarur medical centre, No 5, Javulikara street, Tiruvarur, Tamil Nadu-610001, India.

Case report

26-year old woman (G2P1) was reported to our unit at 30 weeks of pregnancy for a routine ultrasonographic examination. The examination revealed morphologically normal fetus of adequate growth, having irregular cardiac rhythm [video 1] with no signs of cardiac failure or intracardiac abnormalities.

M-mode simultaneous tracing of the right atrial and left ventricular walls showed atrial and ventricular contractions in doubled sequences with a little longer pause between each doubled sequence [Image 1].

Color Doppler of the umbilical arteries showed abnormal fetal cardiac rhythm [Video 2] and pulsed Doppler of the umbilical artery clearly showed bigeminy [Image 2].

The findings were consistent with the premature atrial contractions and bigeminy.

Rest of the antenatal period went uneventful and a healthy male newborn weighing 3200 g. was delivered at term.

Images 1, 2:

Videos 1, 2:

Prevalence

Fetal arrhythmias are encountered in 1 to 2 % of pregnancies [1]. They are classified into three types:
1. Irregular cardiac rhythms;
2. Bradyarrhythmias (heart rate below 110 bpm);
3. Tachyarrhythmias (heart rate above 180 bpm).

Common cause of the irregular cardiac rhythm are premature atrial contractions [PAC] which can be either conducted or blocked resulting in irregular rhythm or short pause respectively [1].

Differential diagnosis

On rare occasions premature beats origins from ventricle and is called premature ventricular contraction [PVC]. Differentiating PAC from PVC is difficult in fetus. Additional findings, like tricuspid regurgitation in color Doppler, small A wave in inferior vena cava pulsed Doppler concurrent with the ectopic beat may be seen in PVC [1].

Blocked atrial bigeminy or trigeminy should be differentiated from AV block. In both conditions, atrial rate is higher than ventricular rate. The time interval between two or three consecutive atrial beat is shortened in bigeminy or trigeminy respectively but it is relatively constant in AV block [1].

Prognosis

PAC are usually benign; 1% to 2% of cases are associated with congenital heart diseases and these cases can progress to sustained tachycardia. Risk factor for progression of PAC to tachycardia is low ventricular rate due to multiple blocked atrial ectopy, bigeminy or trigeminy.

Weekly or biweekly assessment of cardiac rhythm is warranted until PAC resolves or delivery occurs.

References

1. Alfred Abuhamed ,Rabih Caaoui. A practical guide to fetal echocardiography. Wolters kluwer LWW /Second edition 2010, chapter 25, p 351 to 359.