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.

Case report

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.

Image 3: Pulsed-wave simultaneous tracing of the left ventricle inflow-outflow. The transient atrial quadrigeminy pattern is evident in the second PAC (every four atrial contractions there is a premature atrial contraction). Note that the second PAC was premature enough not to be conducted to the ventricle. However this was the only PAC encountered in our study that was blocked and the rest of all the PACs were conducted. The first PAC was not following the quadrigeminy pattern and this is evident from the shape of the E and A waves in the first mitral inflow wave in the trace.

Image 4: Pulsed wave tracing of the main pulmonary artery showing clearly the effect of the atrial quadrigeminy on the ventricular contractions. Note that the ventricular contractions following the PACs are shorter than other ventricular contractions.

Image 5: Pulsed wave tracing of the left ventricle inflow-outflow showing a sporadic PAC interrupting a period of normal heart rhythm.

Image 6: M-mode tracing with the M line passing sequential through the annulus of the tricuspid valve and the right atrium (Tricuspid annular plane systolic excursion TAPSE). The trace is clearly demonstrating the premature atrial contractions in atrial quadrigeminy pattern.

Image 7: M mode tracing with the M line passing sequential through right ventricle, tip of anterior tricuspid valve leaflet and the right atrium with the classic atrial quadrigeminy pattern.

Note: In images 6 and 7, the M mode study clarified the dynamic motion of the tricuspid annulus and the tricuspid valve leaflets during different phases of the regular cardiac cycle as well as during the period of the PAC.  Usual E/A pattern of leaflet motion and undulating wavy pattern of tricuspid annulus movement were seen. However, the pulsed Doppler study revealed that the PAC with consequent small A wave occurs during the period of early diastole and this was evident in dynamic study in figure 6 where we found that during PAC, the tricuspid valve annulus did not move backwards into right atrium because the ventricle started another immediate contraction that kept the annulus in a systolic plane. It was also noted in figure 7 when the PAC occurred; the tricuspid leaflet was starting to open (the usual E motion during early diastole) but it was immediately followed by dynamic effect of the premature ventricular contraction causing rapid closure of the valve leaflet (resulting into a short time of valve leaflet opening represented as a small knob instead of usual E/A pattern of leaflet motion). 

Video 1: M-mode tracing with the M-mode line passing through the right ventricle and the right atrium showing five successive attacks of atrial quadrigeminy (The first two attacks are more evident in the atrial tracing while the three following attacks are more evident in the ventricular tracing).

Video 2: Magnified four-chamber view showing four successive attacks of atrial quadrigeminy followed by a period of normal heart rhythm interrupted by two sporadic PACs then back to one attack of atrial quadrigeminy. 

References:

1- Jeanty P , Chaoui R, Romero R, Pilu G, Goncalves L. Fetal echocardiography: The normal examination. thefetus.net.

2- Weber R, Stamback D, Jaeggi E. Diagnosis and management of common fetal arrythmias. J Saudi Heart Assoc. 2011; 23(2): 61–66.

3- Fouron JC. Fetal arrythmias: the Saint-Justine hospital experience. Prenat Diagn. 2004; 24(13):1068-80.