Home C Cardiovascular Conditions Congenital heart block: Complete AV Block Explained, Risks, Testing, and Long-Term Care

Congenital heart block: Complete AV Block Explained, Risks, Testing, and Long-Term Care

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Congenital heart block is a problem with the heart’s electrical wiring that is present before birth. Instead of signals moving smoothly from the upper chambers (atria) to the lower chambers (ventricles), conduction slows down or stops, and the heartbeat can become dangerously slow. Some babies are diagnosed during pregnancy; others are found at birth or later in childhood when symptoms finally appear. The condition ranges from mild conduction delay to complete (third-degree) heart block, where the atria and ventricles beat independently. The cause matters: some cases are linked to a parent’s autoimmune antibodies during pregnancy, while others occur with congenital heart defects or genetic channel disorders. With modern fetal monitoring, neonatal care, and pacing technology, many children grow into active adults—especially when the diagnosis is timely and follow-up is consistent.

Table of Contents

What congenital heart block is

Your heart beats because an electrical impulse starts in a natural “spark plug” (the sinoatrial node), spreads across the atria, and then passes through a relay station (the atrioventricular, or AV, node) into the ventricles. Congenital heart block means that this AV handoff is slowed or interrupted before birth, so the ventricles do not receive signals normally. The body may compensate by generating a slower backup rhythm, but that backup can be too slow to meet a baby’s or child’s needs—especially during feeding, crying, fever, or exercise.

Clinicians often describe AV block by degree:

  • First-degree AV block: conduction is delayed, but every atrial beat reaches the ventricles. Many children have no symptoms, and the finding may be incidental.
  • Second-degree AV block: some impulses fail to conduct, so ventricular beats are “dropped.” This can be intermittent and may worsen with time in some causes.
  • Third-degree (complete) AV block: atria and ventricles beat independently. Ventricular rates are often slow, and the risk of low blood flow rises.

A key practical distinction is isolated congenital heart block (no major structural heart defect) versus heart block that occurs with congenital heart disease (such as atrioventricular septal defects or other complex anatomy) or after cardiac surgery. Another important category is immune-mediated congenital heart block, where maternal antibodies cross the placenta and injure the fetal conduction system, sometimes leaving permanent scarring.

Why this matters: heart block is not just a number on a monitor. A persistently slow ventricular rate can reduce oxygen delivery to the brain and organs, strain the heart muscle over years, and increase the risk of fainting, heart failure, or dangerous rhythms. The good news is that the condition is highly “trackable” with modern imaging and rhythm monitoring, and when pacing is needed, it can restore reliable heart rates and support normal development in most children.

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What causes congenital heart block

Congenital heart block is a final pathway—electrical interruption—but the reasons behind it are different, and they shape prognosis and treatment. The most common causes fall into three broad buckets: immune-mediated injury, structural heart disease (or surgery), and intrinsic electrical system disorders.

1) Maternal autoimmune antibodies (immune-mediated CHB)
In some pregnancies, antibodies—most often anti-Ro/SSA and anti-La/SSB—cross the placenta and trigger inflammation in the fetal heart. Over time, this can lead to fibrosis and calcification in the AV node and surrounding conduction tissue. A striking feature is that the mother may feel completely well or have mild autoimmune symptoms; the first clue may be fetal bradycardia on a routine ultrasound. Immune-mediated CHB often develops between 16 and 26 weeks of gestation, which is why targeted surveillance in antibody-positive pregnancies typically begins early in the second trimester.

2) Congenital heart disease and anatomy-related causes
Some babies are born with heart defects that distort the conduction pathways or place the AV node in an abnormal position. Examples include atrioventricular septal defects and certain forms of heterotaxy. In these children, heart block may be present from birth or occur later if the conduction system degenerates or is affected by surgical repair.

3) Post-surgical or procedure-related AV block
While this is not “present at birth,” it is still a common reason infants and children develop complete heart block. Operations near the ventricular septum or AV valves can injure conduction tissue. Some post-operative blocks recover within days, while others persist and require a pacemaker.

4) Genetic and channel-related conditions
A smaller group has inherited disorders that affect ion channels or the conduction system’s structure. These may present as bradycardia, conduction disease, or overlap with cardiomyopathies. A strong family history of early pacemakers, unexplained fainting, or sudden death increases suspicion.

Risk factors that raise the index of concern

  • Known maternal anti-Ro/SSA or anti-La/SSB antibodies, especially with a previously affected child
  • Fetal bradycardia noted on prenatal ultrasound (especially persistent rates well below typical fetal norms)
  • Congenital heart defects identified on fetal echocardiography
  • A family history of conduction disease, pacemakers at young ages, or inherited arrhythmia syndromes

Because causes differ, the “right” management plan also differs. Immune-mediated cases raise questions about fetal monitoring and maternal therapies; anatomy-related cases raise surgical and pacing timing questions; genetic cases raise family screening and long-term rhythm planning.

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Early signs and complications

Symptoms depend on the degree of block, how slow the ventricular rate is, and whether the heart muscle remains strong. Some babies show signs before birth, while others appear well until the heart is stressed by growth spurts, illness, or exercise.

During pregnancy (fetal signs)
Often the earliest clue is persistent fetal bradycardia detected on routine prenatal visits. When the heart rate stays slow, the fetus may struggle to maintain normal circulation. Possible complications include:

  • Hydrops fetalis (fluid accumulation in body cavities), a sign of heart failure
  • Poor fetal growth or reduced movement in severe cases
  • Ventricular dysfunction or valve leakage on fetal echocardiography
  • Endocardial fibroelastosis (a stiffening process inside the heart) in some immune-mediated cases

Newborn and infant signs
In the first weeks and months, low heart rate can show up as “subtle” feeding and breathing issues. Watch for:

  • Poor feeding, tiring quickly at the breast/bottle, or sweating with feeds
  • Fast breathing, retractions, or bluish color around lips (especially with exertion)
  • Poor weight gain or repeated vomiting during feeds
  • Unusual sleepiness, low tone, or weak cry
  • Episodes of pallor or near-fainting (harder to recognize in infants)

Childhood and teen symptoms
As activity increases, the gap between what the body needs and what the heart can deliver becomes clearer:

  • Exercise intolerance compared with peers
  • Dizziness, lightheadedness, or fainting (syncope)
  • Chest discomfort or shortness of breath with exertion
  • Headaches or “brain fog” that worsens during sports
  • Palpitations (especially if escape rhythms are unstable)

Complications clinicians monitor for

  • Heart failure due to sustained bradycardia or ventricular dysfunction
  • Dilated cardiomyopathy, which can develop slowly over years in some children
  • Ventricular ectopy or more serious rhythms, particularly if the heart muscle weakens
  • Sudden cardiac events, uncommon but more likely when the ventricular rate is very low, pauses occur, or there is underlying cardiomyopathy
  • Developmental impacts from poor oxygen delivery, especially in infants with severe bradycardia

A practical takeaway: symptoms do not always match the seriousness of the rhythm. Some children “look fine” until a stressor exposes limited heart-rate reserve. That is why congenital heart block is managed proactively with regular rhythm checks and imaging—not only when symptoms appear.

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How doctors diagnose it

Diagnosis is about confirming the type of block, identifying the cause, and measuring how much the rhythm is affecting heart function. The workup typically blends rhythm testing with imaging and, when relevant, maternal or genetic evaluation.

Prenatal diagnosis

  • Fetal echocardiography is the cornerstone. Clinicians assess atrial and ventricular rates, look for AV dissociation, and evaluate heart function, valve regurgitation, and signs of hydrops.
  • Doppler-based measures of the fetal AV interval can help identify early conduction delay before complete block develops.
  • If immune-mediated CHB is suspected, the pregnancy history matters: autoimmune diagnoses, past children with neonatal lupus or CHB, and antibody status.

Newborn and child diagnosis

  • Electrocardiogram (ECG/EKG): confirms AV block degree, atrial and ventricular rates, and QRS width (which provides clues about the level of block).
  • Continuous monitoring (telemetry) or Holter monitor (24–48 hours): captures rate ranges, pauses, intermittent second-degree block, and any ventricular ectopy.
  • Event monitor or patch monitor (days to weeks): useful if symptoms are intermittent or if clinicians are evaluating subtle exercise-related dizziness.

Assessing impact on the heart

  • Echocardiogram (ultrasound of the heart): checks ventricular size and pumping function, valve performance, and any structural defect that might explain the block or worsen tolerance.
  • Exercise testing (in older children/teens): evaluates chronotropic competence (ability to increase heart rate), symptom reproduction, and blood pressure response.
  • Blood tests may be used to assess heart strain or secondary contributors (electrolytes, thyroid function), especially if the clinical picture changes.

Finding the cause

  • Maternal antibody testing (anti-Ro/SSA, anti-La/SSB) is central when congenital block is diagnosed in a fetus or newborn, even if the mother has no autoimmune symptoms.
  • Genetic testing is considered when there is a strong family history, associated cardiomyopathy, unusual ECG features, or when the block is not explained by maternal antibodies or structural disease.
  • Review of medications and exposures during pregnancy is also part of the picture, though most congenital blocks are not caused by a single drug exposure.

How doctors decide urgency
Clinicians look at several “red flags” that push toward more urgent intervention:

  • Very low ventricular rates for age, especially with symptoms
  • Ventricular dysfunction or enlarging heart size on echocardiogram
  • Long pauses, unstable escape rhythms, or complex ventricular ectopy
  • Hydrops or signs of fetal compromise on prenatal imaging

Because conduction disease can evolve, diagnosis is not a one-time event. A child with mild conduction delay today may need closer follow-up during growth spurts, illnesses, puberty, or pregnancy later in life.

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Treatment and what to expect

Treatment is individualized, guided by the block degree, heart rate, symptoms, heart function, and cause. Many children are monitored for years before they need a procedure—while others require pacing early to protect brain and organ perfusion.

Prenatal management (selected cases)
When complete block is established, it is often permanent. Management focuses on fetal well-being and planning delivery in an experienced center. In immune-mediated situations, specialists may discuss maternal therapies intended to reduce inflammation or prevent progression in high-risk pregnancies. Decisions depend on gestational age, signs of fetal heart failure, and the specific rhythm findings. Prenatal care also includes frequent imaging to watch for hydrops, ventricular dysfunction, or valve leakage.

Newborn and infant treatment
If the baby is stable, clinicians may observe closely with continuous monitoring and echocardiography. If the heart rate is too slow or the baby shows poor perfusion (weak pulses, cool extremities, poor feeding, low blood pressure), short-term measures can support circulation while planning definitive therapy. In unstable situations, medications that increase heart rate may be used as a bridge, but they are not a long-term solution for complete block.

Pacemaker therapy
A permanent pacemaker is the most effective long-term treatment for symptomatic high-grade or complete congenital heart block. It does not “cure” the conduction problem; it bypasses it by delivering reliable electrical impulses to maintain an appropriate heart rate.

What to expect with pacing:

  • Timing: implantation may occur in infancy, childhood, or adolescence depending on clinical need.
  • Type of system: very small infants may receive epicardial leads (placed on the heart surface) with a generator in the abdomen; older children often receive transvenous systems (leads through a vein).
  • Goals: prevent fainting, improve feeding and growth, support exercise tolerance, and reduce the risk of bradycardia-related cardiomyopathy.
  • Follow-up: pacemakers require regular checks to adjust settings, monitor battery life, and track lead performance.

Treating associated heart problems
If congenital heart disease is present, treatment may include surgical repair, medications for heart failure, or additional rhythm support. Some children with long-standing bradycardia develop ventricular dilation or reduced function and need standard heart-failure therapies alongside pacing.

Common concerns families have

  • Activity: many paced children can participate in sports with individualized guidance.
  • Device longevity: batteries typically last years, but replacements are expected over a lifetime.
  • Growth: pacing strategies and lead choices consider that children grow; follow-up is essential.
  • School and development: improving reliable cardiac output often improves stamina, sleep quality, and attention—especially when bradycardia was limiting.

The most important expectation is practical: treatment is not a single event but a plan that evolves. Children do best when care is coordinated between pediatric cardiology, electrophysiology, and—when relevant—maternal-fetal medicine and rheumatology.

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Long-term management and when to seek care

Living well with congenital heart block depends on consistent monitoring, smart activity planning, and fast response to warning signs. Even when a child feels fine, clinicians track subtle trends that predict future risk.

Ongoing monitoring typically includes

  • Regular cardiology visits with ECG and periodic Holter/patch monitoring
  • Echocardiograms to watch ventricular size and pumping strength
  • Pacemaker interrogations (in-clinic or remote) to confirm appropriate pacing, battery status, and rhythm events
  • In selected patients, exercise testing to ensure the heart rate response matches activity needs

Everyday habits that help

  • Prioritize sleep and hydration, which can reduce dizziness in slower rhythms
  • Treat fevers promptly and monitor tolerance, since illness increases heart workload
  • Build activity gradually; aim for consistent movement rather than sudden bursts
  • Keep a medical summary available (diagnosis, last ECG findings, device details if paced)

School, sports, and physical activity
Most children can and should be active. The safest plan is individualized, based on:

  • Symptoms (especially dizziness or near-fainting)
  • Ventricular function and any cardiomyopathy
  • Rhythm stability, pauses, and ventricular ectopy
  • Pacemaker dependence and programmed upper pacing limits

Some contact sports may require additional discussion because of device impact risk, but many paced adolescents safely participate in non-contact and even competitive activities with appropriate precautions.

Special considerations for pregnancy later in life
A person born with congenital heart block may reach adulthood and consider pregnancy. Key steps include:

  • Pre-pregnancy cardiology review to confirm ventricular function and device status
  • If the congenital block was immune-mediated, discussion of recurrence risks and monitoring strategies
  • Coordinated care with adult congenital heart disease specialists when anatomy is complex or pacing dependence is high

When to seek urgent care
Call emergency services or seek urgent evaluation for:

  • Fainting, seizure-like episodes, or sudden collapse
  • Severe chest pain, gray/blue color, or trouble breathing at rest
  • New confusion, extreme weakness, or inability to wake fully
  • In paced patients: fever with redness/swelling over the device site, or sudden persistent hiccups/chest twitching that may suggest lead stimulation

Seek prompt (non-emergency) cardiology advice for:

  • New or worsening exercise intolerance
  • Recurrent dizziness, near-fainting, or unexplained falls
  • Rapid weight gain, swelling, or persistent cough (possible heart failure signs)
  • Palpitations, especially if associated with lightheadedness

A useful mindset is to treat congenital heart block like a condition you can manage—because you can. The rhythm may be permanent, but the outcomes are strongly shaped by follow-up quality, timely pacing when indicated, and attention to heart function over time.

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References

Disclaimer

This article is for educational purposes only and does not provide medical advice, diagnosis, or treatment. Congenital heart block can range from mild conduction delay to life-threatening rhythm problems, and care decisions depend on age, symptoms, heart rate, heart structure, and heart function. If you suspect a slow heart rate in a baby, notice fainting or severe dizziness in a child, or have a pregnancy at risk because of autoimmune antibodies, seek prompt evaluation from qualified clinicians. In an emergency—such as collapse, severe breathing difficulty, or blue/gray skin—call local emergency services immediately.

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