1-Radiology department, Kasr Alainy hospitals, Cairo University, Egypt;
2-Edfo general hospital;
3-Fetal medicine Unit, Cairo University, Egypt.
Premature atrial contractions are the most commonly diagnosed fetal arrhythmia. They cause an extra beat or a missed beat on auscultation of fetal heart sound. This is the result of either their electrical conduction or blockage within the AV node. Sometimes they do occur in a bigeminy or a trigeminy pattern. Triggering of a re-entrant phenomenon is a well-known risk resulting in supra ventricular tachycardia. However the overwhelming vast majority of PACs are well-tolerated and self-limited.
A 23-year old, G2P1 woman was referred to our institution due to an abnormal rhythm encountered during auscultation of fetal heart sound. Our ultrasound examination revealed the presence of multiple PACs which were alternating with periods of normal heart rhythm. Although some PACs occurred sporadically and did not respect certain pattern, there were attacks of atrial quadrigeminy (every four atrial contractions there was a PAC). The vast majority of the PACs were conducted to the ventricles except for only one PAC encountered during our scan that occurred prematurely enough to be blocked and we were able to document it by pulsed Doppler technique. After delivery a follow-up of the neonate by ECG one week after delivery revealed complete resolution of the arrhythmia most probably due to maturation of the conduction system.
The normal fetal heart rate narrows the differential diagnosis to premature ventricular contractions which are much less common than PACs. PVCs are associated with regular atrial rate in the majority of cases.
Images 1 and 2: M-mode images obtained with the M line passing through the right ventricle and the right atrium. The transient attacks of atrial quadrigeminy are obvious in these traces. Note the presence of PAC every four atrial contractions which is conducted to the ventricles resulting in the same sequence in ventricular contractions. However this pattern was not respected in the whole scan period and some of the PACs occurred sporadically.