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Progressive cardiac conduction defect (Lenègre)
PCCD gradually impairs the heart's ability to conduct electrical impulses, leading to slow or irregular heartbeats. It can affect individuals at various ages and may require medical intervention to manage heart rhythm.
Overview
Progressive cardiac conduction defect (PCCD) is a condition where the electrical signals that control the heart's rhythm do not travel properly through the heart. This progressive deterioration in the heart's electrical pathways can lead to a slowed heart rate or irregular heartbeats [PMID:17006873]. It is sometimes referred to as Lenègre's disease, named after the French cardiologist Jean Lenègre who described the condition in the mid-20th century. While PCCD can manifest at different ages, symptoms often become more noticeable as the condition progresses. Understanding the underlying genetic causes is important for diagnosis and management.
Symptoms & clinical features
The symptoms of progressive cardiac conduction defect can vary depending on how severely the heart's electrical conduction is affected. Initially, individuals might experience no symptoms at all. As the condition advances, common symptoms can include dizziness, light-headedness, and fainting spells (syncope) [PMID:33618451]. These symptoms typically arise because the heart is beating too slowly to pump enough blood to the brain. Some people may also notice a persistent feeling of tiredness or shortness of breath, particularly during physical activity. Palpitations, where one feels their heart is racing or skipping beats, can also occur.
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Affected organs
Progressive cardiac conduction defect primarily affects the heart, specifically its electrical conduction system. This system is responsible for generating and distributing the electrical impulses that coordinate the contractions of the heart chambers. The condition targets the specialised tissues within the heart, such as the bundle branches and Purkinje fibres, which are crucial for the efficient transmission of these electrical signals. While the heart is the main organ affected, the impact on its ability to pump blood effectively can indirectly influence other organs by reducing blood flow, potentially leading to symptoms like dizziness from reduced brain perfusion.
Risks & severity
The severity of progressive cardiac conduction defect can range from mild, with no obvious symptoms, to severe, potentially leading to significant heart rhythm problems. The condition is progressive, meaning it tends to worsen over time, and the age of onset can vary widely among affected individuals. Some people may develop symptoms in early adulthood, while for others, the condition might only become apparent later in life. A significant risk associated with PCCD is the development of complete heart block, a severe form of arrhythmia where electrical signals from the upper chambers of the heart do not reach the lower chambers. This can necessitate the implantation of a pacemaker to regulate the heart rhythm [PMID:24859265]. The exact prevalence of PCCD is not well established, but it is considered a rare condition.
Genetic causes
Progressive cardiac conduction defect can be caused by pathogenic changes in several genes, including SCN5A and TRPM4. The SCN5A gene provides instructions for making a protein that forms part of a sodium channel. These sodium channels are vital for the initiation and spread of electrical signals within heart muscle cells, allowing the heart to beat in a coordinated manner. When there are pathogenic changes in SCN5A, the sodium channels may not function correctly, disrupting the normal flow of electrical impulses and leading to conduction problems [PMID:17006873].
Another gene implicated in PCCD is TRPM4. This gene provides instructions for making a protein that forms a calcium-activated cation channel. These channels are also involved in the electrical activity of heart cells. Pathogenic changes in TRPM4 can alter the electrical properties of heart muscle cells, contributing to the development of conduction defects. Both SCN5A and TRPM4 play crucial roles in maintaining the heart's electrical rhythm, and disruptions to their function can lead to the progressive slowing or blocking of electrical signals characteristic of PCCD.
- SCN5A sodium voltage-gated channel alpha subunit 5The SCN5A gene provides instructions for creating a crucial component of sodium channels, which are essential for the heart's electrical signalling and rhythm.
- TRPM4 transient receptor potential cation channel subfamily M member 4
Inheritance pattern
Progressive cardiac conduction defect typically follows an autosomal dominant inheritance pattern. This means that an individual only needs to inherit one copy of a pathogenic gene from one parent to develop the condition. If a parent has PCCD, there is a 50% chance with each pregnancy that their child will also inherit the pathogenic gene and therefore be at risk of developing the condition. The condition can affect both males and females equally. It is also possible for PCCD to arise from a new, spontaneous pathogenic change in an individual with no family history of the condition, though this is less common.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
Diagnosis & testing
The diagnosis of progressive cardiac conduction defect often begins with a clinical evaluation, including a review of symptoms and family medical history. Electrocardiograms (ECGs) are a key diagnostic tool, as they can detect abnormalities in the heart's electrical activity, such as a slow heart rate or blockages in electrical conduction. Further investigations may include a Holter monitor, which records heart activity over 24-48 hours, or an exercise ECG.
Once clinical signs suggest PCCD, genetic testing can be performed to identify pathogenic changes in genes like SCN5A and TRPM4. In the UK, genetic testing for inherited cardiac conditions, including PCCD, typically falls under the NHS Genomic Medicine Service (GMS) pathways. Referrals for genetic testing are usually made by cardiologists or clinical geneticists, and testing may be identified through specific R-codes within the GMS, such as R101 Inherited Cardiac Conditions or R163 Cardiac Arrhythmias. A confirmed genetic diagnosis can help guide management and inform family members about their own risks.
Management & lifestyle
Management of progressive cardiac conduction defect focuses on monitoring the heart's electrical activity and addressing symptoms. Regular follow-up appointments with a cardiologist are essential to track the progression of the condition. For individuals who develop significant bradycardia (slow heart rate) or heart block that causes symptoms or poses a risk, the primary treatment is often the implantation of a cardiac pacemaker [PMID:24859265]. A pacemaker is a small device surgically placed under the skin near the collarbone, which sends electrical pulses to regulate the heart's rhythm.
While there is no cure for the underlying genetic cause of PCCD, managing the symptoms with a pacemaker can significantly improve quality of life and reduce serious risks. Lifestyle adjustments, such as avoiding strenuous activities that exacerbate symptoms, may be recommended. Patients and their families are often encouraged to seek support from genetic counsellors, who can provide information about the condition, inheritance patterns, and the implications for other family members, as part of the NHS care pathway for inherited conditions.
UK care pathway
In the UK, individuals suspected of having progressive cardiac conduction defect are typically referred to specialist cardiac services. The NHS Genomic Medicine Service (GMS) provides a framework for genomic testing, with inherited cardiac conditions often falling under specific R-codes for diagnostic testing (e.g., R101 for Inherited Cardiac Conditions). Clinical geneticists or cardiologists usually initiate these referrals. Following a diagnosis, patients will receive ongoing care and surveillance from a multidisciplinary team, often involving cardiologists, electrophysiologists, and genetic counsellors, who provide essential information and support regarding the condition and its inheritance patterns.
Frequently asked questions
What is a pacemaker and why might I need one?
A pacemaker is a small electronic device implanted in your chest to help regulate your heart's rhythm. If progressive cardiac conduction defect causes your heart to beat too slowly or irregularly, a pacemaker can send electrical pulses to ensure your heart maintains a healthy rhythm, improving symptoms like dizziness or fainting.
Is progressive cardiac conduction defect always inherited?
Progressive cardiac conduction defect typically follows an autosomal dominant inheritance pattern, meaning it can be passed down through families. However, it can also occur spontaneously due to a new genetic change in an individual, even if there is no family history of the condition.
How often do I need to be checked if I have PCCD?
If you are diagnosed with progressive cardiac conduction defect, you will typically need regular follow-up appointments with a cardiologist. The frequency of these check-ups will depend on the severity of your condition, your symptoms, and whether you have a pacemaker. Your cardiologist will advise on the appropriate schedule for your care.
Can children get progressive cardiac conduction defect?
While symptoms of progressive cardiac conduction defect often become apparent in adulthood, the genetic changes can be present from birth. Some individuals may develop symptoms earlier in life, including childhood, though it is more commonly recognised in older individuals as the condition progresses.
What is the difference between PCCD and other heart rhythm conditions?
PCCD specifically involves a progressive deterioration of the heart's electrical conduction system, leading to slow heart rates or blocks. Other heart rhythm conditions, like Brugada syndrome or Long QT syndrome, can also be inherited and affect heart rhythm but typically involve different electrical abnormalities and clinical presentations, even if they share some genetic causes like SCN5A.