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Genetic Welfare Problems of Companion Animals
An information resource for prospective pet owners
Labrador Retriever
Tricuspid Valve Malformation
Related terms: Tricuspid valve dysplasia
VeNom term: Tricuspid valve dysplasia (VeNom code: 2022).
Related conditions: oedema; ascites; right-sided congestive heart failure; peripheral oedema; mitral valve dysplasia
Outline: Tricuspid valve malformation is a congenital heart defect, where the valve that regulates the flow of blood between the atrium and ventricle on the right side of the heart is malformed from birth. Defects of the valve affect its functionality and results in less efficient blood flow through the heart. When the right ventricle of the heart contracts it pushes blood, via the pulmonary artery, to the lungs. In affected animals, when the right ventricle contracts, some of the blood leaks back into the right atrium; a process called regurgitation. This back flow of blood alters the pressure and volume of blood entering and leaving the heart, which affects blood circulation around the body and requires the muscles of the heart to work harder. Over time, the tricuspid valves become increasing malformed and the normal compensatory mechanisms of the heart become overwhelmed. This results in a decreased blood flow through the heart. Right-sided congestive heart failure can occur, resulting in peripheral oedema and ascites; this is progressive and fatal in its most severe form.
Clinical signs include abnormal heart sounds (murmur), generalised weakness, exercise intolerance, fainting (syncope), abdominal swelling and fluid accumulation (ascites) and pale mucus membranes (due to poor circulation of the blood). Affected dogs can have a reduced quality of life and a shortened lifespan. Since the abnormalities of the tricuspid valve are present from birth, dogs may start to become affected at an early age eg 1-2 years of age, but the degree of severity of the defect varies between dogs. Mildly affected dogs may live a normal life for several years without clinical signs. Once dogs begin to show signs of regurgitation and congestive heart failure, the prognosis is poor. Evidence of right-side congestive heart failure includes fluid build-up in the abdomen (ascites) and in the tissues, especially in the legs and under the skin (peripheral oedema).
Tricuspid valve malformation commonly affects dogs of large breeds, and in particular, the Labrador retriever breed is significantly predisposed to this condition. The specific gene and/or genetic mechanisms involved in tricuspid valve malformation are not currently known but it appears to be inherited as a simple autosomal dominant genetic disorder in Labrador retrievers. However, not all affected dogs will show clinical signs.
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Summary of Information
(for more information click on the links below)
1. Brief description
Tricuspid valve malformation is a congenital heart defect in which the tricuspid valve, a valve composing of three flap-like pieces of tissue located between the two right chambers of the heart – the right atrium and right ventricle, is malformed. The right atrium of the heart receives deoxygenated blood returning from the body and the right ventricle pumps blood to the lungs, via the pulmonary artery, when it contracts. The tricuspid valve regulates the flow of blood between these two chambers, and shuts to prevent flow of blood back into the atrium when the ventricle contracts. Thickened, shortened or notched tricuspid valves affect the functioning of the valve and allow blood to leak back from the right ventricle into the right atrium each time the ventricle contracts; a process called regurgitation. This ‘backflow’ alters the pressure and volume of blood entering and leaving the heart, making it harder for the heart to fully contract and empty, and affects blood circulation around the body. Over time, the tricuspid valves become increasing malformed, more regurgitation occurs, and the normal compensatory mechanisms of the heart can become overwhelmed, resulting in a decreased blood flow through the heart. Right-sided congestive heart failure can occur, resulting in peripheral oedema and ascites, which is progressive and fatal in its most severe forms.
Clinical signs of a heart defect in affected animals include abnormal heart sounds (murmur), generalised weakness, exercise intolerance, fainting (syncope), abdominal swelling (ascites) and pale mucus membranes (a sign of poor circulation of the blood). Evidence of right-side congestive heart failure includes fluid build-up in the abdomen (ascites) and in the tissues, especially in the legs and under the skin (peripheral oedema).
2. Intensity of welfare impact
The clinical signs of tricuspid valve malformation in affected animals reflect the severity of the individual’s defect. Dogs with small defects may live a normal life with few signs but those with severe tricuspid malformation require more intensive monitoring and care and these dogs will have a shortened lifespan. Dogs may experience episodes of fainting and collapse and periodic weakness and fatigue. Affected dogs will feel unwell and have a significantly impaired quality of life.
With severe heart failure, even mild exercise such as walking will be more difficult. When fluid builds up in the abdomen (oedema/ascites), due to heart failure, dogs may experience abdominal discomfort. These are severe welfare problems and affected dogs are often euthanased.
Severely affected dogs may be at risk of other complications such as changes in heart rhythm (arrhythmias) or infections of the inner lining of the heart (endocarditis), caused by bacterial infiltration. They will cause further welfare problems in of themselves and make the dog feel ill, faint or collapse. Affected dogs require regular monitoring and veterinary check-ups, with more frequent monitoring if there are signs of congestive heart failure. With advanced heart failure, death is likely to occur, and dogs may deteriorate progressively or may die suddenly.
Treatments for heart failure may also cause welfare issues related to the stress caused by travel to and from veterinary practices, hospitalisations, procedures and constant medications. Medications may cause side effects with significant welfare problems.
3. Duration of welfare impact
Since the abnormalities of the tricuspid valve are present from birth, dogs may start to become affected at an early age eg 1-2 years of age. Mildly affected dogs may live a normal life for several years without clinical signs, but the condition is progressive and once dogs begin to show signs of regurgitation and congestive heart failure, the prognosis is poor and lifespan limited. Medical treatment is palliative and aimed at stabilising/improving the dog’s cardiovascular circulation and quality of life, including reducing the amount of abdominal swelling.
4. Number of animals affected
Tricuspid valve malformation commonly affects dogs of large breeds, and in particular, the Labrador retriever is significantly more predisposed to this condition. There is no clear sex predisposition and it affects both males and females in equal proportion.
5. Diagnosis
Since this condition is congenital and present at birth, veterinarians may be able to detect the defect as a heart murmur, at the age of first vaccination. However, mild cases may present only with a faint murmur. Murmurs are categorised on a six point scale from Grade 1, the mildest and least audible, which can be heard with a stethoscope only in a quiet room, to Grade 6, the loudest and most turbulent, which can be heard with the stethoscope not touching the chest, or even without using the stethoscope.
Commonly, dogs with tricuspid valve malformation do not show outward signs, or they are not noticed, until the condition reaches a critical point, where dogs develop severe regurgitation or congestive heart failure. Thoracic radiography and Doppler echocardiography are the most reliable ways to diagnose this disease and determine the severity of regurgitation.
6. Genetics
Tricuspid valve malformation appears to be a simple genetic disorder in Labrador retrievers with autosomal dominant trait characteristics. It affects both sexes equally and an affected individual needs only to inherit one copy of the mutated gene, from either its mother or father, to be at risk of showing the condition. The condition is considered to have incomplete penetrance, however, since not all affected dogs will show clinical signs. The specific gene and/or genetic mechanisms involved in the malformation are not currently known.
7. How do you know if an animal is a carrier or likely to become affected?
There is currently no screening test for tricuspid valve malformation specifically, although the defect may be detected in affected dogs at an early age. Dogs need to inherit one copy of the gene involved, either from their mother or father, to become affected such that approximately half of the offspring of dogs that have inherited a copy of the mutated gene may be affected.
8. Methods and prospects for elimination of the problem
The full mode of inheritance and genetic mechanisms behind tricuspid valve malformation is not yet known, and further research is required to fully understand the condition. Affected dogs should not be bred from, since there is a very high chance of puppies carrying the gene and/or becoming affected themselves.
For further details about this condition, please click on the following:
(these link to items down this page)
- Clinical and pathological effects
- Intensity of welfare impact
- Duration of welfare impact
- Number of animals affected
- Diagnosis
- Genetics
- How do you know if an animal is a carrier or likely to become affected?
- Methods and prospects for elimination of the problem
- Acknowledgements
- References
1. Clinical and pathological effects
Tricuspid valve malformation is a congenital heart defect in which the structures of the tricuspid valve - the leaflets, chordae tendineae and/or papillary muscles are malformed from birth. The tricuspid valve is located between the two right chambers of the heart – the right atrium and right ventricle.
In the normal functioning of the heart, the right atrium receives blood low in oxygen returning from the body. This blood passes to the more muscular walled right ventricle, which contracts and pumps the blood, via the pulmonary artery, to the lungs to receive oxygen and release carbon dioxide. The newly oxygenated blood is then passed to the left heart chambers and is pumped around the body to oxygenate body tissues and organs before being returned to the heart to restart the process.
The tricuspid valve sits between the atrium and ventricle on the right side of the heart and regulates the flow of blood between these two chambers. It consists of three flaps of tissue, called leaflets which form a tight seal when the ventricle contracts to prevent the back flow of blood into the atrium. The leaflets are prevented from ballooning back into the atrium during contraction by strings of tissue called chordae tendineae, which run from the free edges of the leaflet to the ventricle wall (a bit like the strings on a parachute when filled with air which play a vital role in containing that air). In a normal heart the valve leaflets are thin and smooth.
In dogs with this condition, the malformed tricuspid valves can appear thickened, shortened or notched (Lui & Tilley 1976). These defects affect the normal functioning of the valve and allow blood to leak back from the right ventricle into the right atrium each time the ventricle contracts; a process called regurgitation. This increases the volume of blood in the right atrium, and results in the normally thin muscular walls of the atrium becoming thickened. The heart also has to contract more forcefully to pump the blood from the ventricle and blood pressure increases in the right side of the heart and connected blood vessels. In turn this extra work also causes the muscular walls of the right side of the heart to thicken.
As the right side of the heart increases in size, the deformation of the tricuspid valve gets worse, due to the increased pressure on the valve during the more forceful contraction of the ventricle. More blood is regurgitated and blood flow through the heart decreases. This impairment to normal blood circulation results in liver dysfunction and accumulation of fluid in the abdomen (ascites). Over time, the normal compensatory mechanisms of the heart become overwhelmed, significantly more regurgitation occurs, and congestive right-side heart failure, with oedema and ascites, may occur. This is a progressive disease and fatal in its most severe forms.
Dogs affected with tricuspid valve malformation will likely have abnormal heart sounds (murmur), and severely affected dogs may have vibrations (during regurgitation) felt externally during a chest examination. The external jugular veins located on either side of the neck may be enlarged or distended. Clinical signs of tricuspid valve malformation include generalised weakness, exercise intolerance, fainting (syncope), abdominal swelling (ascites) and pale mucus membranes (eg the gums - a sign that can indicate poor circulation of blood). There is an association between tricuspid valve malformation and other congenital anomalies, in particular mitral valve malformation or pulmonic stenosis (Chetboul et al 2004). Evidence of right-side congestive heart failure include fluid build-up in the abdomen (ascites) and in the tissues especially in the legs and under the skin (peripheral oedema)..
2. Intensity of welfare impact
The clinical signs of tricuspid valve malformation in affected animals reflects the severity of the individual’s defect. Dogs with small defects may live a normal life. Dogs with moderate malformation may have certain aspects of their life restricted, for example, they may be unable to cope with repeated periods of prolonged exercise or exposure to extreme temperatures. With severe tricuspid malformation, dogs need more intensive monitoring and care and these dogs will likely have a shortened lifespan. Severely affected dogs may find it difficult to engage in energetic activities such as running or vigorous play. Dogs may experience episodes of fainting and collapse and periodic weakness and fatigue. Affected dogs will feel unwell and have a significantly impaired quality of life.
With severe heart failure, even mild exercise such as walking will be more difficult. When fluid builds up in the abdomen (oedema/ascites), due to heart failure, dogs may experience abdominal discomfort. Severely affected dogs may be at risk of other complications such as changes in heart rhythm (arrhythmias) or infections of the inner lining of the heart (endocarditis), caused by bacterial infiltration. They will cause further welfare problems in of themselves and make the dog feel ill, faint or collapse. These are severe welfare problems and affected dogs are often euthanased.
Affected dogs require regular monitoring, and veterinary check-quarterly intervals may be recommended. More frequent evaluation would be advisable if there are signs of congestive heart failure. With advanced heart failure, death is likely, and dogs may deteriorate progressively or may die suddenly. Investigations for heart failure and treatments may also cause welfare issues related to the stress caused by travel to and from veterinary practices, hospitalisations, procedures and constant medications. Medications may cause side effects with significant welfare problems.
3. Duration of welfare impact
Since the abnormalities of the tricuspid valve are present from birth, dogs may start to become affected at an early age eg 1-2 years of age. Mildly affected dogs may live a normal life for several years without clinical signs, but the condition is progressive and once dogs begin to show major signs of regurgitation and congestive heart failure, the prognosis is poor and lifespan limited. Medical treatment is palliative and aimed at maximising heart function and stabilising/improving the dog’s quality of life, specifically in reducing congestion and the amount of abdominal swelling (ascites). Dogs in or likely to develop congestive heart failure can be placed on a sodium-restricted diet, and given medications to regulate blood pressure and prevent fluid build-up. Valve replacement surgery is the only definitive cure for tricuspid valve malformation, but this is a complex surgery and currently not widely available.
4. Number of animals affected
The prevalence of tricuspid valve malformations in the general population is currently unknown. We do know that it is one of the most common of all congenital heart defects found in dogs (Tidholm 1997, Oliveira et al 2011).
Tricuspid valve malformation commonly affects dogs of large breeds, and in particular, the Labrador retriever is reported to be significantly more predisposed to this condition. In a study of dogs with tricuspid valve malformation in an Italian veterinary hospital, Labrador retrievers had a significantly increased risk of tricuspid malformation diagnosis, 11 times greater than other breeds (Oliveira et al 2011). In France, it was found that Labradors were 35 times more at risk of being affected by tricuspid valve malformation than other breeds (Chetboul et al 2004).
There is no clear sex predisposition for tricuspid valve malformation, as appears affects both males and females in equal proportion.
5. Diagnosis
Since this condition is congenital and present at birth, veterinarians may be able to detect the defect as a heart murmur, at the age of first vaccination. However, mild cases may present with only a very faint murmur. Murmurs are categorised on a six point scale from Grade 1, the mildest and least audible, which can be heard with a stethoscope only in a quiet room, to Grade 6, the loudest and most turbulent, which can be heard with the stethoscope not touching the chest, or even without using the stethoscope.
Commonly, dogs with tricuspid valve malformation do not show outward signs, or they are not noticed, until the condition reaches a critical point, where dogs develop severe regurgitation or congestive heart failure. The first clinical sign of tricuspid valve malformation which owners might notice is usually abdominal swelling (ascites).
Thoracic radiography and Doppler echocardiography are the most reliable ways to diagnose this disease and determine the severity of regurgitation.
6. Genetics
Tricuspid valve malformation in Labrador retrievers appears to be a highly heritable disorder passed from parent to offspring (Famula et al 2005), and the result of a simple genetic disorder in Labrador retrievers with autosomal dominant trait characteristics (Andelfinger 2003). It affects both sexes equally and an affected individual inheriting one copy of the mutated gene, from either its mother or father, is at risk of showing the condition. The condition is considered to have incomplete penetrance however, meaning not all affected dogs will show clinical signs, and the degree of severity is unpredictable. Researchers identified a region on canine chromosome 9 (CFA9) in which the disease is presumed to lie (Andelfinger 2003), though the specific gene involved in the malformation is not currently known.
Little is known about the genetic mechanisms leading to valvular heart disease and there are several breed-related predispositions to congenital heart disease, not just limited to defects in the tricuspid valve. Therefore, systematic screening for heart murmurs for all breeding animals is advised, and where persistent murmurs are detected, further investigation and diagnosis of congenital cardiac conditions. In particular, Labrador retrievers may be predisposed to developing other conditions affecting the heart, including pulmonic stenosis (narrowing of pulmonary valve) and persistent arterial duct stenosis.
7. How do you know if an animal is a carrier or likely to become affected?
There is currently no screening test for tricuspid valve malformation specifically; though the defect may be detected in affected dogs at an early age with the presence of a heart murmur. The trait is monogenic dominant, which means that dogs need to inherit one copy of the gene involved, either from their mother or father, to become affected, indicating that approximately half of the offspring of dogs that have inherited a copy of the mutated gene may be affected.
8. Methods and prospects for elimination of the problem
Although dogs with a mild form of tricuspid dysplasia have a low risk of developing symptoms of the condition, it is still important to identify these dogs for the purpose of eliminating the condition from the breed (Farrell et al 2015), since mildly affected and asymptomatic dogs may pass on a more severe form of the condition to their offspring due to the dominant mode of inheritance. However, the problem is made more complex because not all affected dogs will show clinical signs, and will therefore not be diagnosed, but will carry the genetic defect and this may lead to tricuspid dysplasia in later generations.
It is advisable that all dogs used for breeding should be screened for heart defects by echocardiogram, and the screening results of relatives should be taken into consideration. Affected dogs should not be bred from, since half of their puppies will inherit the gene and may be affected themselves.
9. Acknowledgements
UFAW thanks Dr Emma Buckland (BSc PhD), Dr David Brodbelt (MA VetMB PhD DVA DipECVAA MRCVS) and Dr Dan O’Neill (MVB BSc MSc PhD MRCVS) for their work in compiling this section.
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10. References
Andelfinger G (2003) Canine tricuspid valve malformation, a model of human Ebstein anomaly, maps to dog chromosome 9. Journal of Medical Genetics 40: 320–324
Chetboul V, Tran D, Carlos C, Tessier D and Pouchelon JL (2004) Congenital malformations of the tricuspid valve in domestic carnivores: A retrospective study of 50 cases. Schweizer Archiv für Tierheilkunde 146: 265–75
Farrell LL, Schoenebeck JJ, Wiener P, Clements DN and Summers KM (2015) The challenges of pedigree dog health: Approaches to combating inherited disease. Canine Genetics and Epidemiology 2: 3
Famula TR, Siemens LM, Davidson AP and Packard M (2002) Evaluation of the genetic basis of tricuspid valve dysplasia in Labrador Retrievers. American Journal of Veterinary Research 63: 816–820
Liu SK and Tilley LP (1976) Dysplasia of the tricuspid valve in the dog and cat. Journal of the American Veterinary Medical Association 169: 623–30
Oliveira P, Domenech O, Silva J, Vannini S, Bussadori R and Bussadori C (2011) Retrospective Review of Congenital Heart Disease in 976 Dogs. Journal of Veterinary Internal Medicine 25: 477–483
Tidholm A (1997) Retrospective study of congenital heart defects in 151 dogs. Journal of Small Animal Practice 38: 94–8
© UFAW 2016
Credit for main photo above:
By Erikeltic at English Wikipedia [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
