Dr. Alessandro Giardini
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If you have been told that your baby or child has congenital heart block, it is completely natural to feel anxious. A slow heart rate in a baby, especially one detected before birth or soon after delivery, can sound very worrying. The reassuring news is that congenital heart block is a well-understood condition, and with modern monitoring, pacemaker technology and specialist cardiac care, the long-term outlook is excellent. Many children with this condition grow up to lead full, active lives.
Dr Giardini regularly assesses and follows babies and children with slow heart rhythms and congenital heart block. He can provide a clear explanation of the diagnosis, guide you through the decision about whether and when treatment is needed, and ensure that your child receives the right follow-up at every stage.
The heart's electrical system normally works in a coordinated sequence. A natural pacemaker in the upper chambers (the atria) generates an electrical signal that travels through a specialised pathway called the atrioventricular (AV) node to reach the lower chambers (the ventricles), triggering them to contract and pump blood to the body. In heart block, this signal is delayed or interrupted.
There are different degrees of severity. First-degree heart block means the signal is delayed but still reaches the ventricles. Second-degree heart block means some signals get through and some do not. Complete heart block, also called third-degree AV block, means the electrical signal from the atria is entirely unable to pass through to the ventricles. The atria continue to beat at their normal rate, but the ventricles must rely on their own backup pacemaker, which generates a much slower rhythm. This means the heart beats more slowly than normal, which can reduce the amount of blood pumped to the body.
When heart block is present from birth or is diagnosed during pregnancy, it is called congenital heart block. Complete congenital heart block affects approximately 1 in 15,000 to 1 in 20,000 live births, making it a rare but clinically important condition. It is the form that usually requires the closest monitoring and the one most likely to need treatment.
The severity varies considerably. Some babies and children have a stable slow heart rhythm and remain well for a long time. Others may develop symptoms because the heart rate is too slow to meet the body's needs. The key factors Dr Giardini assesses are whether the baby or child has symptoms, how slow the heart rate is, whether the heart muscle is functioning normally, whether there are associated structural heart problems, and whether the rhythm remains stable over time. In many cases, the condition can be managed safely with careful follow-up. When the heart rate is too slow or symptoms develop, a pacemaker may be needed, and pacemakers are well-established, highly effective treatments in children that allow a normal, active life.
There are two main causes, and understanding which applies to your child is an important part of the assessment.
Maternal autoimmune antibodies are the most common cause of congenital complete heart block in babies with a structurally normal heart. Mothers who carry specific antibodies called anti-Ro (SS-A) and anti-La (SS-B) can pass these antibodies across the placenta during pregnancy, typically between 18 and 24 weeks of gestation. These antibodies can cause inflammation and damage to the developing conduction system of the foetal heart, leading to scarring and fibrosis of the AV node. The mother may have a known autoimmune condition such as systemic lupus erythematosus (SLE) or Sjögren syndrome, but in many cases the mother is entirely well and the antibodies are discovered only after the baby is diagnosed with heart block. The risk of congenital heart block in pregnancies exposed to anti-Ro/La antibodies is approximately 1 to 2%, rising to 12 to 20% in subsequent pregnancies if a previous child has been affected.
It is extremely important for mothers to understand that this is not something they caused or could have prevented. The antibodies are part of the mother's immune system and their effect on the baby's heart is an unpredictable and unavoidable consequence that occurs in only a small proportion of exposed pregnancies.
Structural congenital heart defects are the second major cause. Some complex heart conditions, including congenitally corrected transposition of the great arteries (ccTGA) and heterotaxy syndromes, are associated with abnormal development of the AV node, which can result in complete heart block either before or after birth. In these cases, the heart block is part of a broader cardiac condition that requires comprehensive assessment.
In a smaller number of children, complete heart block develops during childhood without maternal antibodies or structural heart disease. Some of these cases are linked to genetic variants affecting the cardiac conduction system, and genetic testing may be recommended.
Congenital heart block is frequently diagnosed before birth. During a routine foetal ultrasound or a specialist foetal echocardiogram, the sonographer or cardiologist may notice that the baby's heart is beating unusually slowly (foetal bradycardia), typically at a rate of 50 to 80 beats per minute compared with the normal foetal heart rate of 120 to 160. Further assessment with foetal echocardiography confirms that the atria and ventricles are beating independently, which is the hallmark of complete AV block.
If heart block is suspected prenatally, the mother's blood is tested for anti-Ro and anti-La antibodies to determine whether the block is autoimmune in origin. Dr Giardini can arrange for a detailed foetal echocardiogram to assess the severity of the block, check for any signs of heart failure (such as fluid accumulation around the baby, known as hydrops fetalis), evaluate the heart's structure, and help plan delivery and postnatal care.
After birth, congenital heart block is confirmed by an electrocardiogram (ECG), which shows a characteristically slow ventricular rate with complete dissociation between atrial and ventricular activity. An echocardiogram is performed to assess heart function, check the structure of the heart, and look for any associated abnormalities. Dr Giardini performs and interprets all echocardiograms personally, so findings can be discussed with you immediately.
Some children develop complete heart block later in infancy or childhood rather than before birth. In these cases, the diagnosis may be prompted by an unexpectedly slow pulse, fatigue, poor feeding, breathlessness, poor weight gain, unusual tiredness, dizziness, fainting (syncope), reduced exercise tolerance or a pale or grey colour. In more severe cases, there may be signs of heart failure. A baby with a very slow heart rate, poor feeding, lethargy or breathing difficulty needs urgent assessment. A 24-hour Holter monitor recording is often used alongside the ECG and echocardiogram to assess the heart rate across the full range of daily activities and sleep, including the lowest heart rate during the night.
When congenital heart block is identified before birth, care involves a coordinated team including foetal cardiologists, foetal medicine specialists and obstetricians. The pregnancy will typically require regular foetal echocardiograms to monitor the rhythm, heart function and signs of foetal wellbeing, maternal blood testing for anti-Ro and anti-La antibodies, and planning for delivery in an appropriate specialist centre with neonatal cardiac facilities.
It is worth knowing that complete heart block can make labour monitoring more complex, because the baby's heart rate is already slow and the usual markers of foetal distress on the heart rate trace may not apply in the standard way. Delivery planning therefore requires careful discussion between the cardiology, foetal medicine and obstetric teams. Dr Giardini can be involved in this planning to ensure the cardiac assessment is in place from the moment the baby is born.
Management options during pregnancy are limited, but foetal monitoring plays an important role. If the heart block is caused by maternal autoimmune antibodies and is identified at an early stage (first or second degree block), the mother may be given dexamethasone, a steroid medication that crosses the placenta and may reduce inflammation in the fetal heart. However, once complete (third-degree) heart block is established, it is usually irreversible regardless of treatment.
If the foetus shows signs of heart failure, early delivery may be planned so that postnatal treatment can begin. In pregnancies where a previous child has been affected, hydroxychloroquine given to the mother from early pregnancy has been shown to reduce the risk of recurrence. Close foetal surveillance throughout pregnancy, typically with fortnightly echocardiograms from around 16 weeks, is recommended for all at-risk pregnancies.
Not immediately, and not always, but the majority will need one at some point during childhood. This is one of the most important topics Dr Giardini discusses with families, because the timing of pacemaker implantation is a carefully considered decision rather than an emergency.
A pacemaker does not cure the heart block, but it prevents the heart from going too slowly. It provides the ventricles with a reliable electrical signal so they beat at an appropriate rate, allowing the heart to pump enough blood to meet the body's needs.
Some babies are born with a ventricular rate that is fast enough to maintain adequate circulation and grow normally. These children can be monitored closely without a pacemaker, at least initially. Published guidelines recommend pacemaker implantation for newborns and infants with a ventricular rate below 50 to 55 beats per minute, or below 70 beats per minute if there is an associated structural heart defect. A pacemaker is also indicated if the child develops symptoms (fatigue, poor feeding, dizziness,), if the heart begins to enlarge or its function declines on echocardiography, or if there are prolonged pauses or wide QRS complexes on the ECG or Holter monitoring.
The large French nationwide study published in 2024, following 385 children with isolated non-immune AV block, found that 74% eventually required a pacemaker, with 60% receiving one before the age of 10. In the majority, pacemaker implantation was prophylactic rather than in response to an acute event. This underscores the importance of regular follow-up: even children who appear well may develop indications for pacing as they grow.
For families, it is worth knowing that pacemaker technology has advanced enormously. Modern pacemakers are small, reliable and long-lasting, and the implantation procedure is safe even in very young babies. Pacemaker therapy should not be associated with the stigma of a device used only in elderly patients. In children, it is a highly effective treatment that restores a normal heart rate, supports growth and development, and allows full participation in everyday life.
The approach depends on the child's age and size.
In newborns and infants, epicardial pacemaker leads are used. These are thin wires placed directly onto the surface of the heart through a small incision in the chest (often a subxiphoid approach, just below the breastbone). The leads are connected to a small pulse generator, which is typically placed in a pocket in the abdominal wall. This approach avoids the blood vessels, which are too small in babies for the standard adult approach. The surgery is performed under general anaesthetic and is well tolerated, with most babies recovering within a few days.
In older children and teenagers, transvenous pacemaker leads can be inserted through a vein (usually the subclavian vein below the collarbone) and positioned inside the heart chambers. The pulse generator is placed in a small pocket under the skin below the collarbone, similar to the standard adult approach. This is a less invasive procedure with a quicker recovery.
Pacemaker batteries last approximately five to eight years, depending on usage, and battery replacement is more straightforward than implantation and can be undertaken as a day-case procedure or with a short hospital admission. Lead replacement may be needed occasionally as the child grows, particularly if epicardial leads placed in infancy lose their effectiveness over time. Dr Giardini can coordinate all aspects of pacemaker care and follow-up.
This depends on the type and cause. Milder forms, such as first-degree heart block, may remain stable indefinitely or occasionally improve. Second-degree heart block can sometimes progress to complete block over time, which is one reason why ongoing monitoring is important even when the initial degree of block appears mild.
Complete congenital heart block caused by autoimmune antibody-related damage to the AV node is usually permanent. The scarring and fibrosis that disrupt the conduction pathway do not reverse. However, even when the heart block itself does not go away, children can still do very well with appropriate monitoring and pacemaker therapy when indicated.
The long-term outlook for children with congenital complete heart block is very reassuring. With appropriate monitoring and, when indicated, pacemaker therapy, long-term survival exceeds 90%, and the large majority of children enjoy a normal quality of life. A UK tertiary centre study following 72 patients with paced congenital heart block reported 0% mortality over a mean follow-up of 21 years, with 88% of patients in the best functional class at the end of the study.
Most children with pacemakers attend school normally, participate in sport (with some common-sense precautions around contact to the pacemaker site), and grow and develop without restriction. Dr Giardini provides individualised exercise guidance for each child based on their specific cardiac function and pacemaker settings.
A small number of children with congenital heart block can develop a late cardiomyopathy (weakening of the heart muscle), which is thought to be related to the long-term effects of chronic right ventricular pacing or to the underlying autoimmune process itself. This is an important reason why lifelong follow-up with echocardiography is recommended, even when the child is well and the pacemaker is functioning normally. Modern pacing strategies, including cardiac resynchronisation therapy when appropriate, can help address this complication if it arises.
Children with heart block associated with structural heart disease have a more variable outlook depending on the complexity of their underlying condition, but outcomes continue to improve with advances in surgical and pacing techniques.
Children with congenital complete heart block require regular, lifelong follow-up. Whether or not a pacemaker has been implanted, Dr Giardini arranges periodic assessments including clinical examination, ECG, 24-hour Holter monitoring and echocardiography. For children with pacemakers, device checks are performed to assess battery life, lead function and pacing thresholds. The frequency of follow-up depends on the child's age, symptoms and pacemaker status, but appointments are typically every six to twelve months.
Whether your baby has been diagnosed with heart block before birth, your child has been found to have a slow heart rate after delivery, or you have an existing diagnosis and would like a second opinion on the need for or timing of pacemaker implantation, Dr Giardini can provide a comprehensive assessment with same-day echocardiography and a clear explanation of the diagnosis, treatment options and outlook.
Congenital heart block is a condition present from birth in which the electrical signals that coordinate the heartbeat are delayed or blocked between the upper and lower chambers of the heart. In the most severe form, complete heart block, no signals pass through at all and the heart beats using a slower backup rhythm. It affects approximately 1 in 15,000 to 1 in 20,000 births.
The two main causes are maternal autoimmune antibodies (anti-Ro and anti-La, associated with conditions such as lupus and Sjögren syndrome) and structural congenital heart defects. In many cases, the mother is entirely well and the antibodies are discovered only after the baby is diagnosed.
No. This is not something any parent caused or could have prevented. When related to maternal antibodies, the effect on the baby's heart is an unpredictable event that occurs in only a very small proportion of exposed pregnancies.
Milder forms may remain stable or sometimes improve. Complete congenital heart block, particularly when caused by autoimmune antibody-related damage, is usually permanent. However, it is very treatable, and most children do extremely well with appropriate monitoring and pacemaker therapy when needed.
Many children with congenital heart block will need a pacemaker at some point, but not all require one immediately. The decision is based on the heart rate, symptoms, heart function and growth. Dr Giardini will guide you through this decision carefully.
Yes. Pacemaker implantation is well established even in newborns and small infants. The procedure is performed under general anaesthetic with very low complication rates. Modern pacemakers are small, reliable and last approximately five to eight years before a straightforward battery replacement is needed.
Yes. Most children with pacemakers attend school, play sport and lead completely normal lives. Some precautions are needed around direct contact to the pacemaker site in contact sports, but most activities are unrestricted. Dr Giardini provides individualised activity guidance for each child.
Yes. It is often diagnosed during pregnancy when a slow foetal heart rate is detected on ultrasound. Foetal echocardiography confirms the diagnosis and allows the medical team to plan delivery and postnatal care.
If you have had one child with congenital heart block, the risk in subsequent pregnancies is approximately 12 to 20%. Hydroxychloroquine given from early pregnancy has been shown to reduce this risk. Close fetal monitoring with regular echocardiograms is recommended from around 16 weeks.
Lifelong follow-up is recommended, including regular ECGs, Holter monitoring and echocardiograms. For children with pacemakers, periodic device checks assess battery life and lead function. This ongoing monitoring ensures that any changes are detected early.
When should I see a specialist?
If your baby has been diagnosed with a slow heart rate before or after birth, if heart block has been suspected or confirmed, or if you carry anti-Ro/La antibodies and are planning a pregnancy, specialist assessment is recommended. The specialist can provide a definitive diagnosis, guide pacemaker decision-making, and ensure appropriate long-term follow-up.
Author: Dr. Alessandro Giardini, MD, PhD
Written 03/04/2026