eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology
Atrioventricular Block, Third Degree, Congenital
Updated: Feb 2, 2009
Introduction
Background
Third degree atrioventricular block is seen in a fetus or a neonate younger than 28 days. Complete atrioventricular dissociation with bradycardia is observed.
Congenital atrioventricular block (CAVB) can occur in a structurally normal heart (isolated CAVB) or with congenital heart disease (complex CAVB with congenital heart defects).
Isolated CAVB occurs in the absence of other congenital heart defects. It is seen in association with certain autoimmune antibodies in the mother that cross the placenta and damage the atrioventricular (AV) node of the fetus. The mother can be completely asymptomatic in presence of these autoimmune antibodies or may have a diagnosis of a collagen vascular disease (eg, systemic lupus erythematosus, Sjögren syndrome).
Isolated CAVB can also occur due to myocarditis and rarely hereditary conditions such as storage disorders (eg, Hurler syndrome, Hunter syndrome). Often, no etiology is found for an isolated CAVB.
CAVB can also be seen with certain congenital heart defects, most often complex defects such as heterotaxy with accompanying AV canal defects and L-transposition of the great arteries.
Pathophysiology
Isolated CAVB is thought to be the result of transplacental passage of certain autoantibodies (immunoglobulin G [IgG] antibodies against Ro and La intracellular ribonuclear proteins), from the mother who may have a clinical autoimmune disease such as systemic lupus erythematosus or Sjögren syndrome or who may be clinically asymptomatic. These autoantibodies damage the AV conduction tissue by inflammation in the early stage and later by fibrosis.
CAVB with structural heart disease is considered to be caused by failure of the AV conduction system to develop during heart development. This may be a result of increased distance between the AV node and the ventricular conduction tissues.
Frequency
International
Autoimmune AV block occurs in approximately 1 per 14,000-20,000 live births. However, because significant fetal loss is thought to result from this disease, the true incidence of the disease (per conception) may be significantly higher. Structural congenital heart block is also rare but with a higher proportion of fetal loss.
Mortality/Morbidity
The fetal mortality rate of isolated CAVB may be as much as 30-50%. Patients diagnosed and treated in the neonatal period have a survival rate of 94%, and patients who are diagnosed and treated in childhood have a survival rate of 100%.
Risk factors for death in patients with isolated CAVB include fetal diagnosis, very low heart rate, low birth weight, premature gestation, male gender, hydrops fetalis, endocardial fibroelastosis, and diminished ventricular function. Hydrops fetalis is the risk factor for patients with structural heart disease and CAVB.
Fetal and newborn mortality rates in congenital heart block with structural heart disease remain high, even if effective pacing is used.
Patients with L-transposition of the great arteries or with well-repaired structural heart defects typically have a better overall outcome than infants with complex structural cardiac defects and/or ventricular dysfunction.
Sex
The prevalence of isolated CAVB may be slightly higher in females than in males.
Age
Patients who present with symptoms as fetuses or newborns may have a more severe course or may require earlier pacing than those who present with symptoms later in childhood.
Clinical
History
Congenital atrioventricular block (CAVB) may be identified during prenatal examinations, in the perinatal period, or during childhood or adulthood. Historical and other features widely vary and particularly depend on the timing of presentation and accompanying structural heart disease.
- Isolated CAVB
- A minority of mothers confirmed to have a fetus with autoimmune atrioventricular (AV) block have symptoms solely related to autoantibodies. Occasionally, the mothers may have a history of recurrent fetal loss. Fetuses of such mothers should be routinely evaluated for CAVB.
- The mother is often completely asymptomatic. The fetus in whom isolated CAVB is identified during the prenatal period usually presents with an incidental finding of bradycardia or hydrops fetalis.
- In addition to fetuses who are incidentally identified, siblings of children with known isolated heart block usually undergo fetal ultrasonographic screening because the recurrence rate for heart block in subsequent siblings is 17-22%.
- In the perinatal period, fetal bradycardia may also be an incidental finding. However, when persistent bradycardia is identified in the third trimester, emergency delivery is sometimes inappropriately carried out without differentiating acute causes of bradycardia related to fetal distress from the more chronic condition of isolated CAVB.
- Some centers recommend cesarean delivery and preterm delivery for fetuses with CAVB and hydrops fetalis.
- Newborns with congenital heart block may present with a hydropic appearance secondary to fetal heart failure or may develop signs of low cardiac output or failure within hours to days after birth. However, affected newborns often appear asymptomatic and may have accelerated ventricular rates approaching those of healthy newborns. Congenital heart block is not likely to be identified in many such infants until well after birth. An associated finding in autoimmune or isolated CAVB may be the presence of discoid skin lesions.
- In older infants or children, signs of low cardiac output due to bradycardia, such as pallor, mottling, lethargy, exercise intolerance, palpitations, dizziness, or syncope, may occur. Children may have sleep disturbances or be asymptomatic.
- CAVB with structural heart disease
- The diagnosis of a congenital heart defect in one child or first-degree relative is an indication for fetal echocardiography to check for cardiac malformations.
- Children with structural heart defects may present with cyanosis, failure to thrive, or recurrent pneumonias or may be completely asymptomatic in childhood, such as children with L-transposition of the great arteries and intact ventricular septum.
Physical
The fetus is remote from physical examination but may be monitored with ultrasonography. In the newborn, the findings may range from asymptomatic to signs of congestive heart failure and low cardiac output.
- The most typical physical finding is a low heart rate for age. Because the block is usually complete and the escape rhythm is usually junctional in origin, a regular rhythm at 60-80 beats per minute (bpm) is often found. Auscultation demonstrates a variable first heart sound caused by the AV asynchrony.
- Congenital AV block may be associated with findings of low cardiac output or congestive heart failure. Low cardiac output may manifest with physical findings of irritability or lethargy, cool skin, mottling, or cyanosis.
- Congestive heart failure may manifest with tachypnea and hepatomegaly. If congestive heart failure has been present prenatally, marked edema may be part of the complex of hydrops fetalis.
- Children with neonatal lupus can present with rash, neurological and hepatic manifestations. The rash can occur some days after birth and is worsened with sun exposure. Annular or elliptical erythematous plaques can be present on the skin of face, scalp and extremities. It usually resolves without scarring but can be associated with residual hypopigmentation or rarely telangiectasias.
- Children with structural heart disease may manifest symptoms and signs related to the specific congenital heart defect. Patients with heterotaxia syndrome and unbalanced AV canal defects may be cyanotic. Patients with L-transposition of the great arteries may be completely asymptomatic or may demonstrate a murmur.
Causes
Isolated CAVB has been described since 1901. In some cases, it has been related to the presence of maternal connective tissue disease since the early 1970s.
- Autoimmune CAVB is presumed to be caused by injury from the placental passage of maternal anti-Ro and anti-La (or related) antibodies, which are present in more than 90% of mothers during pregnancy or at the time of delivery. CAVB occurs in as many as 5% of children born to mothers with anti-Ro antibody. Children with isolated complete CAVB are most likely to have acquired the disease as a complication of subclinical or clinical maternal lupus erythematosus, maternal Sjögren syndrome, or another maternal autoimmune disease. As such, they may have other manifestations of neonatal lupus syndrome in the newborn period and other cardiac sequelae of neonatal lupus during follow-up treatment. This may also be true of infants who are born to these mothers but do not manifest AV block. Other complications of maternal autoimmune disease include second-degree AV block and cardiomyopathy.
- Often, no clear etiology is determined for isolated CAVB. Rarely, it can occur as a result of myocarditis, infiltrative disease, or cardiomyopathy. Hereditary diseases such as Hurler cardiomyopathy and Hunter cardiomyopathy can be associated with CAVB.
- Complex CAVB is associated with congenital heart defects that have structural abnormality of the conduction system. These heart defects are usually complex but may be simple as a ventricular septal defect.
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Further Reading
Keywords
third degree congenital atrioventricular block, third-degree congenital atrioventricular block, CAVB, congenital heart block, congenital complete heart block, congenital complete atrioventricular block, atrioventricular, AV, congential complete AV block, congential complete A-V block, autoimmune complete heart block, 3° atrioventricular block, 3° AV block, 3° A-V block, collagen vascular disease, systemic lupus erythematosus, Sjogren syndrome, Hunter syndrome, Hurler syndrome, myocarditis, hydrops fetalis, endocardial fibroelastosis, L-transposition of the great arteries, ventricular septal defect
