May 13, 2020
Years published: 1988, 1989, 1997, 1998, 2006, 2020
NORD gratefully acknowledges Caroline Najjar, MD Candidate, McGill University School of Medicine, and Akanksha Agrawal, MBBS, Resident Physician, Department of Internal Medicine, Albert Einstein Medical Center, for assistance in the preparation of this report.
Congenital heart block (CHB), or atrioventricular block (AVB), is characterized by interference of the transfer of the electrical nerve impulses (conduction) that regulate the normal and rhythmic pumping action of the heart muscle. The severity of such conduction abnormalities varies among affected individuals.
The normal heart has four chambers. The two upper chambers are the atria and the two lower chambers are the ventricles. In order for the heart to contract and pump blood to the body, it needs an electrical stimulus to signal contraction. The SA (sinoatrial) node, which is located in the right atrium, acts as a natural pacemaker that initiates and controls the heartbeat. The electrical stimulus travels from the SA node in the atrium to the ventricles along a very specific path of conducting tissue via the AV (atrioventricular) node located at the junction between the atria and ventricles. The AV node mediates proper transmission between the top and bottom chambers so that every atrial contraction is accompanied by ventricular contraction. To allow for ventricular contraction, the signal travels down the bundle branches in the His-Purkinje system, which is the electrical pathway located in the septum (the heart muscle between the two ventricles). To summarize, the SA node allows for atrial contraction, the AV node allows for transmission of the signal between the atria and ventricles, and the His-Purkinje system allows for ventricular contraction. As long as the electrical impulse is transmitted normally, the heart behaves and contracts normally allowing for blood to be pumped out to the body.
If the transmission of the signal is impeded, the blocked electrical transmission is known as a heart block or an AV block. The disturbance may be transient or permanent. This condition does not affect the flow of blood and does not lead to the blockage of coronary arteries (which would lead to a heart attack). It is an electrical problem rather than a hydraulic one.
Heart blocks are categorized according to the degree of impairment of the patient and the pattern of conduction abnormality. The categories are first, second, and third degree heart block. Second degree heart block is further characterized into two types: Mobitz type I and Mobitz type II. CHB can happen at any age but is termed congenital when it occurs in the fetus or newborn up to 28 days of life. Individuals may progress from one type of heart block to a more severe degree.
The presentation of congenital heart block varies with age of onset, underlying etiology, and type of heart block.
In newborns affected by CHB, the primary finding is a slow heart rate (bradycardia). Individuals may also appear pale or diaphoretic, have intermittent gallops and murmurs, and show signs of congestive heart failure (e.g. crackles in lungs, peripheral edema, etc.).
Some individuals may present with CHB later in childhood. The primary finding is also a slow heart rate (bradycardia), which may or may not be present with bradycardia-related symptoms such as decreased exercise tolerance and presyncope or syncope (Stokes-Adams attacks). Heart block may be intermittent at first and become persistent over time.
In first degree heart block, the two upper chambers of the heart (atria) beat normally, but the contractions of the two lower chambers (ventricles) slightly lag behind because it takes a longer time for the electrical impulse to move from the SA node to the AV node. If the time taken for the impulse to move from the atria to the ventricles is longer than 0.2 seconds, but no other abnormalities are present, first degree heart block is present. Most people with this mild form of the disorder do not experience any symptoms (asymptomatic). Some affected individuals may fatigue quickly and experience difficulty breathing (dyspnea).
Second degree heart block is characterized by dropped or skipped beats. This signifies that some signals sent from the SA node in the atrium do not reach the ventricles because they are “blocked” or “stopped” at the AV node. Therefore, not all contractions of the atria will be followed by contractions of the ventricles. This form of the disorder may be separated into two subgroups which have different presentations: Mobitz type I (Wenckebach) and Mobitz type II.
In Mobitz type I AV block, there is a progressive delay between heartbeats until a beat is dropped or skipped. Because the consequences are usually limited to short-term dizziness and modest fatigue, the condition is not considered dangerous and has excellent prognosis.
Mobitz type II AV block is more rarely encountered and usually carries greater risks. It is characterized by an extremely low heart rate because most of the electrical impulses generated by the SA node in the atrium cannot get to the ventricles. Thus, the number of heartbeats is reduced. Often, affected individuals may fatigue quickly and/or experience difficulty breathing (dyspnea) and/or episodes of unconsciousness (syncope). It is, however, not uncommon for affected individuals to be symptomless (asymptomatic). In some people, a pacemaker may be inserted into the upper chest to restore normal heart rhythm.
In third degree or complete heart block, none of the electrical signals from the SA node in the upper chamber reach the lower chambers. In order for the ventricles to contract, the His-Purkinje system (bundles of specialized nerves in the electrical conduction system) takes over as a natural pacemaker in the lower chambers. Thus, the atria and ventricles beat independently of one another and are not in sync because they are controlled by two different areas that do not communicate (the SA node controls the atria and the His-Purkinje system controls the ventricles). Individuals with complete heart block may experience episodes of unconsciousness (syncope), breathlessness, lack of energy (lethargy), and/or low blood pressure (hypotension). In addition, complete heart block may be associated with an impaired ability of the heart to pump blood effectively (congestive heart failure); chest pain and/or palpitations; episodes of dizziness with or without loss of consciousness due to heart fluttering (fibrillation) or cessation (asystole) of the heart (Stokes-Adams attacks); and/or enlargement of the heart (cardiomegaly). In rare cases, infants born with complete heart block may have abnormal accumulation of fluid within tissues of the body (hydrops fetalis). Treatment with a pacemaker is necessary to restore natural heart rhythm.
Over half the cases of congenital heart block (60-90 percent) are associated with an autoimmune disorder in the affected individual’s mother such as systemic lupus erythematosus or Sjogren’s syndrome. This results in a passively acquired autoimmune disease in the child termed neonatal lupus. Autoimmune disorders occur when the body’s natural defenses against foreign or invading organisms (antibodies) begin to attack healthy tissue for unknown reasons. Congenital heart block may result when maternal antibodies cross the placenta, enter the fetus, and attack the fetal cardiac conduction system. The antibodies that were originally produced by the mother’s body to fight infections recognize parts of the conduction system in the fetal heart as foreign and abnormally attack and damage the tissues, resulting in inflammation and scarring which leads to faulty conduction. Neonatal lupus may present with other symptoms such as cutaneous lupus lesions and liver abnormalities, though these symptoms normally resolve after a few months of age when the maternal antibodies have been cleared. The heart conduction system abnormalities, on the other hand, are irreversible. Autoimmune heart block is typically of the third degree and begins in utero, while heart block due to other causes tends to present after birth and may be first, second, or third degree. In fact, up to 40 percent of AV block cases do not present until later in childhood, out of which only around 5 percent are of autoimmune origin. (For information on neonatal lupus, choose “lupus” as your search term in the Rare Disease Database.)
Congenital heart blocks may or may not be associated with structural abnormalities of the heart. Almost half of children diagnosed in utero (during pregnancy have structural heart disease. When diagnosed in the postnatal period (after birth), approximately one-third have structural heart disease. There are several types of heart anomalies that can occur with abnormal fetal development, some of which are more prone to accompanying developmental anomalies of the AV conduction tissues. These include L-looped (levo) transposition of the great arteries, endocardial cushion defects, and atrial septal defects (ASDs). The most common congenital heart diseases associated with AV block are levo transposition and left atrial isomerism, which is often associated with an ASD. Presence or absence of structural heart defects significantly impact prognosis and treatment.
There is also a genetic form of congenital heart block that is seen in non-immune cases without structural heart defects, which is described as an idiopathic disorder having a familial tendency. It may be inherited in an autosomal recessive pattern, although some researchers do not rule out an autosomal dominant pattern of inheritance.
In some cases, congenital heart block may occur as a secondary characteristic of certain disorders or tumours of the heart muscle (myocardium).
Congenital heart block is a rare disorder that appears to affect males and females in equal numbers. In the general population, the incidence varies between 1 in 15,000 to 1 in 22,000 live births. The incidence of complete (third degree) congenital heart block is one in approximately 20,000 to 25,000 live births.
The recurrence rate of congenital heart block in subsequent pregnancies in women who have had an affected child is 15 percent.
The prenatal diagnosis of congenital heart block is more common as cardiac imaging techniques are improving. A growing number of autoimmune cases are being diagnosed between 18 and 24 weeks of pregnancy, leading to a better prognosis. Diagnosis depends on the results of one or more cardiac imaging tests such as fetal electrocardiography (ECG) and fetal echocardiography. This may help determine the type of heart block and may rule out any structural heart anomalies.
If congenital heart block is overlooked during pregnancy or if the physician prefers to wait for the birth of the baby, diagnosis is commonly confirmed during infancy or early childhood.
There are limited management options for congenital heart block in utero, but fetuses are often able to tolerate slow escape rhythms. If a more severe degree of heart block is present, adrenocorticosteroids such as dexamethasone may be prescribed to the mother as this class of medication is not metabolized by the placenta. Dexamethasone works to decrease inflammation and the number of circulating maternal antibodies in the fetus. If signs of fetal distress such as hydrops fetalis (abnormal accumulation of fluid within tissues of the body) are present, dexamethasone is also given but an early delivery may be required with emergency pacing.
For newborns and children with CHB, the main therapy is insertion of a pacemaker. In affected individuals who exhibit mild forms of heart block (such as first degree or second degree Mobitz I), treatment may not be required. More severe cases (such as second degree Mobitz II and third degree heart block) may require a temporary or permanent pacemaker. Permanent insertion of a pacemaker may be recommended for individuals with Stokes-Adams attacks, congestive heart failure or significant cardiomegaly, or infants with a ventricular rate of less than 55 beats per minute. Ultimately, most (~90 percent) people with congenital heart block will require a pacemaker regardless of the age of onset of symptoms. The type of pacemaker needed depends primarily on the age of onset and the presence or absence of congenital heart defects.
If hypotension and bradycardia occur alongside Mobitz type I, treatment can consist of the administration of atropine, a drug that temporarily increases the AV conduction in the heart. Patients with other types of CHB are usually unresponsive to atropine.
The prognosis of patients with congenital heart block depends largely on the following factors: presence or absence of underlying structural heart disease, rate of ventricular activation and presence or absence of congestive heart failure. Presence of bradycardia (slow heart rate), congestive heart failure and structural heart disease are usually poor prognostic markers. Prognosis is better for infants diagnosed after the newborn period.
Information on current clinical trials is posted on the Internet at https://clinicaltrials.gov/. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Toll-free: (800) 411-1222
TTY: (866) 411-1010
Some current clinical trials also are posted on the following page on the NORD website:
For information about clinical trials sponsored by private sources, contact:
For information about clinical trials conducted in Europe, contact:
There are currently (2019) fourteen studies listed on the Clinical Trials website related to congenital heart block, half of which have been completed. Most are related to the treatment and/or prevention of this disease, as well as its genetic characterization.
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