Cairo University Fetal Medicine Unit

Atrioventricular reentrant tachycardia (AVRT) is one of the electrophysiological mechanisms of supraventricular tachycardia and in most cases the conduction occurs via a fast accessory pathway which is demonstrated in pulsed Doppler interrogation as a short VA interval¹. The increased frequency of the presence of these accessory pathways may be linked to the immaturity of the fetal conductive tissues ². In some occasions it is feasible to demonstrate a premature atrial contraction switching this reentrant mechanism on and off ³. The rate is regular and is about 180-300 bpm⁴ and is typically around 240 bpm⁵ and the atrioventricular relationship is 1:1 ⁴. Establishing the type of fetal tachycardia is extremely important for the choice and the success of a certain pharmaceutical agent ¹. Digoxin is the first line of treatment in AVRT if no hydrops is associated but is not equally effective in hydropic fetuses where other agents like Sotalol play a role^3,5.

Case Report
A 28-year-old (G2P1) with irrelevant history was referred to our unit at the 31 week of gestation due to a tachycardia noticed during fetal heart auscultation. Our ultrasound examination revealed the presence of a fetal tachycardia (around 240 bpm) with 1:1 atrioventricular conduction. Further study showed the presence of a short VA tachycardia suggesting the presence of a supraventricular tachycardia due to an atrioventricular reentrant mechanism through a retrograde fast accessory pathway. There was moderate ascites in the fetus. Management included administration of digoxin in addition to adenosine but conversion was not successful after few days and thus adenosine was replaced with sotalol which managed to convert the heart rhythm. Delivery by C-section at the 37 week of gestation due to an obstetric indication and the course was uneventful up to one week after delivery.

Video 1: demonstrates the tachycardia and shows the structural integrity of the heart. Ascites can also be visualized

Image 1 and Video 2: Simultaneous M-mode tracing of both the right ventricle and the left atrium showing tachycardia (240 bpm) with 1:1 atrioventricular conduction. Note the presence of short VA interval as demonstrated in the video.

Images 2, 3, 4 and Video 3: simultaneous pulsed wave interrogation of both the aorta/SVC and renal artery/renal vein emphasizing on the 1:1 atrioventricular conduction and showing the short VA interval. In image 3 the SVC tracing below the baseline is not evident however on the aortic side (above the baseline) the short VA interval is strikingly evident.

References

1. Oudijk MA, Visser GH, Meijboom EJ. Fetal tachyarrhythmia--part I: Diagnosis. Indian Pacing Electrophysiol J. 2004; 4: 104-13.

2. Bravo-Valenzuela NJ, Rocha LA, Machado Nardozza LM, Araujo Júnior E. Fetal cardiac arrhythmias: Current evidence. Ann Pediatr Cardiol. 2018; 11: 148-163.

3. Fouron JC, Fournier A, Proulx F, et al. Management of fetal tachyarrhythmia based on superior vena cava/aorta Doppler flow recordings. Heart. 2003; 89: 1211-6.

4. Weber R, Stambach D, Jaeggi E. Diagnosis and management of common fetal arrhythmias. J Saudi Heart Assoc. 2011; 23: 61-6.5. Simpson JM. Fetal arrhythmias. Ultrasound Obstet Gynecol. 2006; 27: 599-606