* Fetal medicine unit, Cairo University, Egypt;
** Om El Masryeen Hospital; Cairo, Egypt;
*** Imbaba Hospital, Cairo, Egypt;
**** Radiology department, Kasr Alainy hospitals, Cairo University, Egypt;

Complete heart block is the end result of a destructive process that affects the cardiac conductive tissue and leads to atrio-ventricular dissociation that results in bradycardia and may end in heart failure ¹. A link to an immune mediated destructive process involving trans-placental passage of anti-Ro/SSA and/or anti-La/SSB that damage the fetal myocardiocytes is now well established ¹. Structural heart disease should be ruled out in fetuses of complete heart block since it accompanies a significant proportion (about 50%) of these fetuses specifically left isomerism and discordant atrio-ventricular connections ^{1, 2}. In one study, Lopes et al. retrospectively reviewed 116 cases of complete heart block diagnosed in their institution over 18 years. They identified the association with structural heart disease, ascites, atrial rate below or equal to 120 and ventricular escape rate below 55 as risk factors for mortality². The presence of structural heart disease is an ultimately poor prognostic sign and in particular left isomerism ^{2, 3}. Management strategies vary significantly between one center to the other with highly controversial data present in the literature about the efficacy of corticosteroids, beta stimulation and other medications taking into consideration their adverse fetal and maternal effects ^{1, 3}. The role of maternal steroids may be more beneficial for resolution of fetal hydrops if occurred in cases of complete heart block^1,3. This controversy extends to the prophylactic approaches with IV immunoglobulin and hydroxychloroquine most commonly used for that purpose¹. 

Case report

A 24-year old PG woman presented to Cairo University Fetal Medicine Unit at the 32 week of gestation because of persistent bradycardia noted both by fetal heart auscultation and an ultrasound study performed during her antenatal care. Our ultrasound examination revealed the following:

- Cardiomegaly with thick, hypertrophied ventricular free walls.

Images 1 and 2: M-mode tracing of both the right atrium and the left ventricle obtained with different sweep speeds. Note the regular atrial contractions at a rate of approximately 102 bpm and the regular ventricular contractions at a much slower rate (around 42 bpm) with evident atrio-ventricular dissociation.

Images 3 and 4: color M-mode tracing demonstrating both the flow in the left atrium and the aortic outflow, also confirming the regularity of both atrial and ventricular contractions with different rates being much slower at ventricular level. Note also the atrio-ventricular dissociation.

Images 5 and 6: simultaneous pulsed wave insonation of both left ventricular inflow and outflow demonstrating the atrio-venticular dissociation with the slow ventricular rate. Note that one of the atrial contractions was not evident on the trace (red star) as it occurred during closure of the mitral valve. Note also, the absence of E wave in the mitral inflow waveform that accidentally occurred prior to a ventricular contraction.

Images 7 to 11: simultaneous Doppler insonation of both the ascending aorta and SVC demonstrating both the forward flow in the ascending aorta and the reversed component of venous flow in the SVC occurring during the phase of atrial contraction. The trace clearly demonstrates the atrio-ventricular dissociation and both the atrial and the ventricular rates. Note in images 9 and 10, atrial contractions which are synchronous with ventricular contractions are taller (Canon A waves).

Videos 2, 3, 4, 5: demonstrate the structural integrity of the fetal heart including the normal situs and the concordant atrio-ventricular and ventriculo-arterial connections denoting absence of any structural defects in the heart which is a very important prognostic factor in cases of complete heart block. Note the cardiomegaly and the vigorous systolic arterial distension of aorta and pulmonary arteries.

Video 6: four chamber view with color Doppler clearly showing the left and right ventricular inflow pattern and the evident regurgitation across both tricuspid and mitral valves.

References:

1.  Hunter LE, Simpson JM. Atrioventricular block during fetal life. J Saudi Heart Assoc 2015; 27:164-178

2. Lopes LM, Tavares GM, Damiano AP, Lopes MA, Aiello VD, Schultz R, Zugaib M. Perinatal outcome of fetal atrioventricular block: one-hundred-sixteen cases from a single institution. Circulation 2008; 118:1268-75.

3. Simpson JM. Fetal arrythmias. Ultrasound Obstet Gynecol 2006; 27:599-606.