Introduction
Congenital heart block (CHB), or atrioventricular block (AVB) is a condition that affects the normal rate, rhythm, and heart functioning. It occurs following a disturbance to the electrical nerve impulses that cause the pumping action of the heart muscle. Most congenital heart blocks (60 % to 90 %) are associated with an autoimmune disorder.
What Is Autoimmune Congenital Heart Block?
Autoimmune disorders occur when the body’s natural immune system (against foreign organisms- antibodies) begins to attack the body’s healthy tissue. The mother’s body naturally produces antibodies to fight infections. In the presence of an autoimmune disorder, these antibodies attack and damage the tissues of the fetal heart and cause inflammation, scarring, and calcification of the atrioventricular node, which leads to faulty conduction.
Autoimmune congenital heart block (CHB) is an immune-mediated acquired disease that is associated with the placental transfer of maternal autoantibodies specific for Ro (also called SSA- Sjögren-syndrome-related antigen A) and La (also called SSB- Sjögren-syndrome-related antigen B). The severity of autoimmune congenital heart block varies among affected individuals.
When Does Autoimmune Congenital Heart Block Begin?
Autoimmune heart block can occur at any age but is termed congenital when it begins in utero or in newborns up to twenty-eight days old. Anti-Ro and anti-La antibodies cross the placenta as early as eleven weeks of gestation and cause inflammation, calcification, and scarring of the fetal conduction tissues, which subsequently blocks signal conduction at the atrioventricular (AV) node in an otherwise structurally-normal heart.
Autoimmune congenital heart block is a form of complete heart block (third-degree) since no electrical signals from the upper chamber reach the lower chambers. Subsequently, the atria and ventricles do not beat together in a synchronized manner.
What Are the Symptoms of Autoimmune Congenital Heart Block?
The symptoms of autoimmune congenital heart block can vary among individuals depending on the age, severity, and location of the damage. Some possible symptoms may include:
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Slow heart rate (bradycardia).
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Episodes of unconsciousness (syncope).
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Breathlessness, lack of energy (lethargy).
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Low blood pressure (hypotension).
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Blue or purple tint to the skin or lips (cyanosis).
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Heart failure to pump blood effectively (congestive heart failure).
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Chest pain.
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Palpitations.
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Enlargement of the heart (cardiomegaly).
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Difficulty feeding or poor weight gain in infants.
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Electrophysiological abnormalities such as:
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Sinus node dysfunction (sinus node, part of the heart, does not function normally).
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Ventricular tachycardia (faster heartbeat at the ventricles of the heart).
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Junctional tachycardia (faster heart rate at the junctions of the heart chamber).
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Long QT interval (indicates the heart takes a longer break between heart beats).
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Atrial flutter (a condition where the heart rhythm in the atria is very fast).
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Valvular disease (when the structure of the valve is damaged due to injury or a disease condition).
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Dilated cardiomyopathy (a condition where blood flow is less due to an enlarged and weakened heart).
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A condition called hydrops fetalis, where fluid accumulation within the tissues of the body occurs in an abnormal manner is seen rarely in some children who are born with a complete heart block.
What Causes Autoimmune Congenital Heart Block?
The exact cause of autoimmune congenital heart block is not known. However, some studies believe that it is related to an autoimmune response in which the immune system mistakenly targets the heart's electrical system.
In some cases, autoimmune congenital heart block may be associated with a mother's autoimmune disease (such as systemic lupus erythematosus (SLE) and Sjogren's syndrome) during pregnancy, as antibodies produced by the mother's immune system can cross the placenta and attack the developing fetus's heart.
In other cases, autoimmune congenital heart block may occur without any apparent maternal autoimmune disease, suggesting that it may be caused by genetic factors or other environmental factors (such as toxins or infections) that trigger an autoimmune response.
How Is Autoimmune Congenital Heart Block Diagnosed?
Autoimmune congenital heart block is usually diagnosed in utero, at birth or within the neonatal period (0 to 27 days after birth). The diagnosis of autoimmune congenital heart block is made by physical examination, family history, or medical history of the mother, along with certain tests, which are as follows:
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Echocardiography- Scans for abnormalities inside of the heart.
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Electrocardiogram (ECG) - The abnormal electrical activity of the heart is measured using this test.
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Chest X-Ray - In order to check for presence of fluid or blood accumulation in the heart or lungs indicative of heart disease.
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Pulse Oximetry - Measures the amount of oxygen present in the blood.
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Cardiac Catheterization- A catheter is inserted into the blood vessel through an artery or vein into the heart to assess the heart pressure. A colored, X-ray-detectable dye may also be injected through the catheter to study the functioning and shape of the heart (angiogram) for any structural heart anomalies.
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Blood Tests- To check for maternal autoantibodies for Ro and La.
How Is Autoimmune Congenital Heart Block Treated?
Factors such as age, severity, and symptoms of the condition are considered before choosing the appropriate treatment modalities.
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Corticosteroids - Transplacental administration of corticosteroids if the fetal PR interval is >150 ms, and the first-degree atrioventricular block is diagnosed. It does not necessarily improve the condition of the heart and prevent the use of pacemakers, however, it does improve the overall health condition of the fetus. However long-term use of corticosteroids can affect the fetus’s growth and hence risks over benefit analysis must be done before the use of transplacental corticosteroids.
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Maternal Oral Dexamethasone - If congenital heart block is advanced to the second degree.
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Intravenous Immunoglobulin (IVIG) and Plasmapheresis - A treatment regimen consisting of Dexamethasone 4 mg/d throughout pregnancy, weekly plasmapheresis, and IVIG 1 g/kg every two weeks was shown to be beneficial for suffering fetuses.
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β-Sympathomimetic Agent - As an alternative drug to increase fetal heart rate and improve myocardial contractility.
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Pacemaker - The pacemaker implantation is recommended for symptomatic patients and asymptomatic patients who have profound bradycardia, left ventricular dysfunction, a wide QRS interval, or a prolonged QT interval. Almost all children were placed within the first year of life and nearly two-thirds were within ten days of birth. Regular follow-up is strongly recommended for patients with pacemaker implantation since recent studies have shown heart failure and the risk of developing complications associated with intracardiac materials.
How Can Autoimmune Congenital Heart Block Be Prevented?
Since the exact cause of autoimmune congenital heart block is unknown, there are no strict prevention protocols. However, some measures may help reduce the risk of developing an autoimmune congenital heart block.
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Management of Maternal Autoimmune Disease- If the mother is known to be suffering from an autoimmune disease such as systemic lupus erythematosus, then timely monitoring of the mother’s health and medications to control the autoimmune activity is required.
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Prophylaxis Treatment: Studies have shown that the maternal administration of Hydroxychloroquine (HCQ) plays a vital role in preventing congenital heart block and significantly decreased the occurrence of congenital heart block. It is indicated for prophylaxis in pregnant women with a previous child affected by congenital heart block.
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The Use of Intravenous Immunoglobulin-G (IVIG) - To prevent the recurrence of congenital heart block where maternal autoantibodies specific for Ro and La are present.
Conclusion.
A close follow-up is required for all children affected with autoimmune congenital heart disease since the affected individuals have been known to have an increased risk of cardiovascular comorbidity and a higher risk of infection. The use of maternal prophylaxis with Hydroxychloroquine is very important and is recommended in all pregnant women at risk for the recurrence of autoimmune congenital heart block. However, the beneficial effects of the medications can be achieved only when they are administered within a strict time window.