Also, in some rare cases, the congenital heart block was linked with viral infections or treatment with specific medications. Maternal autoimmune disease
In the autoimmune-mediated congenital heart block, autoantibodies are passively transferred through the placenta during gestation. The mother might be asymptomatic during or after pregnancy but she is usually positive to anti-Ro\SSA or anti-La\SSB antibodies. In this case, the fetuss heart is normally developed and shows no structural malformations. Just like other autoimmune diseases, the autoimmune CHB shows signs of damage resulted from the autoantibodies attacking the normal tissue of the body, inflammation and fibrosis in the fetal heart tissue are the most common ones, mainly in the atrioventricular node. These antibodies lead to irreversible injuries in the atrioventricular node which heavily compromise the efficiency of the electrical conduction system, and this results in around 18% mortality rate and 70% of the live-born kids will need early pacemaker implantation. Anti-Ro\SSA autoantibody
This autoantibody is found in the serum of the majority of kids with autoimmune CHB, and therefore it is the one mostly linked with this disease. It attacks the proteins Ro52 and Ro60 in the antigen Ro\SSA in the fetal heart tissue.
In addition, levo transpositions of the great arteries can accompany CHB but this is less common than the first one.These developmental abnormalities can impair the conduction system of the heart by disrupting its anatomical structure. Diagnosis
There is  a difference in diagnosis between low risk pregnancies where mothers do not have (or are not aware of) any autoimmune disease, and the high risk ones where mothers are known to have a specific autoimmune disease and / or are positive to anti Ro/La autoanitbodies and / or had a CHB-affected pregnancy previously.In low risk pregnancies, testing the mothers serum is not part of the routine prenatal tests. Therefore, the congenital heart block is usually diagnosed during a routine obstetrical ultra sound. The first symptom in most cases is a slow heart rate which can be detected using fetal echocardiogram and Doppler ultra sound techniques between the weeks 18 - 30. The Doppler is very important to assess the level of AV block as well as to check for other cardiac structural abnormalities that might be associated with CHB such as left atrial isomerism, valvular damages and big arteries inversion, while the echocardiogram is useful to detect other complications such as the hydrops fetalis. In the absence of cardiac structural diseases, the second step to confirm the diagnosis is to test the serum of the mother for anti Ro/La autoantibodies using the enzyme-linked immunosorbent assay (ELISA).In high risk pregnancies, the diagnosis is relatively easier as fetal and maternal screenings are part of the routine monitoring of the pregnancy.