Fetal Complete Congenital Heart Block
One may appreciate the slow heart rate of the ventricles. We can also see that the atrial rate (right atrium) seems faster than the underlying ventricular rate.
4 chamber with colour to visualize the inflow, as well as output via the LVOT and RVOT.
There is some trivial tricuspid regurgitation. Inflammatory changes to the papillary muscles may occur in the context of the myocardial inflammation secondary to transplacental passage of maternal auto-antibodies (Anti-Ro, Anti-La). Significant atrio-ventricular valvular insufficiency may occur in this context.
Despite the low heart rate, there seem to be subjective appropriate biventricular contraction, as well as absence of clear endofibroelastosis, which may occur in the context of transplacental passage of Anti-Ro / Anti-La (SSa/SSb) antibodies in the context of maternal rheumatological conditions that may lead to congenital heart block by inflammatory changes / fibrosis of the fetal atrio-ventricular node and overall conductive system / myocardium.
Short axis demonstrating the slow bi-ventricular heart rate by B-mode
Sweep from the short-axis to the arch view.
Colour in arch view indicates that the blood flow corresponds to the ventricular rate.
These clips outline the contractions of the atriums at a faster rate than the ventricular contraction. The M-Mode (Ventricular-Atrial) will help characterize further the entity.
Ventricular rate of 53 bpm
M-mode outlining that the atrial rate is 161 bpm and the ventricular rate is 52 bpm.
Evaluation of the atrial and ventricular rates by M-Mode
Dopplers outlining the underlying ventricular rate
Views outlining the low ventricular rate. One may perceive the faster atrial contraction on the B-Mode. This will be better exemplified by the M-Mode (better temporal resolution), allowing for evaluation of atrial and ventricular rates and relationship.
M-Mode outlining that the ventricular rate is 66 bpm, while the atrial rate is 140. There is no clear relationship between the atrial and ventricular rates.
Doppler in the arch may be used to estimate the ventricular rate.
Dopplers in a fetus exposed to an Anti-Ro+ pregnancy but without any evidence of congenital heart block:
Normal atrivoentricular (AV) time interval (mitral-aortic) at 107 msec, (superior vena cava (SVC)-aorta) at 97 msec
Normal atrio-ventricular conduction on M-mode
Functional AV block (blocked premature atrial contractions) or atrial bigeminy may be mistaken at times for complete heart block.