Genetic Welfare Problems of Companion Animals

English Bulldog

Pulmonic Stenosis

Related terms: Pulmonary valve stenosis

Outline: Pulmonic stenosis is a congenital narrowness or constriction of the outflow from the right side of the heart. It occurs much more commonly in the English bulldog than on average for dogs and is believed to have a genetic basis, probably involving several genes. If the constriction is mild there may be no welfare effects but when more severe it can lead to right-side heart failure causing chronic malaise.

Summary of Information

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1. Brief description

Pulmonic stenosis (PS) is a common hereditary heart abnormality of dogs (Patterson 1989). Bulldogs are particularly predisposed to the condition and it is in this breed that it occurs most commonly (Buchanan 2001). If severe, it can lead to exercise intolerance, right-sided heart failure, and premature death.

Stenosis is the narrowing of the pulmonary blood supply from the right ventricle to the lungs. It obstructs normal blood flow. In dogs, the stenosis can occur at one of three places: supra-valvular (above the level of the valve of the heart); valvular (at the level of the valve) and sub-valvular (below the level of the valve) (Rishniw 2004). The commonest form in most breeds is due to dysplasia of the tricuspid valve that separates the upper and lower chambers of the right side of the heart (Ryan no year), but in English bulldogs another form is also commonly seen (Buchanan 2001). This form is due to an abnormality of the left coronary artery, which entraps and constricts the outflow from the heart near the level of the pulmonary valve (Buchanan 1990, et al 2002, Kittleson et al 1992). Buchanan (2001) suggested that this form may cause the majority of cases of PS in the English bulldog.

Cases can be mild, moderate or severe. Usually, only severe stenosis causes clinical signs. These signs include fatigue, progressive exercise intolerance (which usually shows as breathlessness on exercise), and, in some cases, syncope (sudden collapse and fainting). Ascites (fluid accumulation in the abdominal cavity) and distension of the jugular veins occur as the right side of the heart fails to pump blood forward efficiently. Dogs with severe PS are also prone to heart arrhythmias which may lead to syncope and weakness.

Colour flow Doppler ultrasonography can be helpful in determining the cause and severity of the stenosis. Treatment is generally not considered necessary in mild to moderate cases.

2. Intensity of welfare impact

When the stenosis (causing constriction of the blood supply to the lungs) is mild or moderate, affected dogs may show no signs. In more severe cases, right-sided heart failure develops (Stafford Johnson 2006) and affected dogs lack energy, are likely to feel unwell and to be unable to exercise properly. There may be episodes of breathless, fainting and collapse.  There may be sudden death due to progression of the heart failure.

Investigations and treatments for PS may also cause welfare issues related to stress and side effects of the medication given to treat the condition.

3. Duration of welfare impact

Signs of pulmonic stenosis, once apparent, are life-long (unless the disease can be successfully treated).

4. Number of animals affected

In a large survey of dogs in the USA, English bulldogs were found to have the highest breed prevalence of pulmonic stenosis, it being 19 times more common in the breed than is normally seen in dogs. However, a far as we are aware, there are no data available on the proportion of English bulldogs affected. Male dogs are more vulnerable than females (Buchanan 1992). English bulldogs are also predisposed to another heart defect of the ventricular septum (Buchanan 1992).

5. Diagnosis

Detection of a ‘harsh’ heart murmur in any young English bulldog is indicative of a potential heart defect, and suggestive of PS as this is the commonest congenital heart defect in the breed (Buchanan 2001). Confirmation of PS is usually made using colour-flow Doppler ultrasonography.

6. Genetics

Pulmonic stenosis has been shown to be an inherited condition in beagles (Patterson 1984) and it is probable that this is the case in other breeds with a predisposition for the condition. PS is thought to be a polygenetic threshold trait: the occurrence and severity of the disease depends on which combinations of a range of genes they have inherited (Patterson 1989). The genes involved have not been determined.

7. How do you know if an animal is a carrier or likely to become affected?

Affected individuals can be detected early in life by listening to the heart (auscultation) using a stethoscope during veterinary examination. All puppies should have a veterinary examination prior to purchase. It is not known whether animals can carry the genes that cause the condition without developing the disease themselves, although this seems likely, and there is no way to detect such carriers at present.

8. Methods and prospects for elimination of the problem

As far as we are aware there are no breeding programmes aimed at reducing the prevalence of PS from the English bulldog breed. However, it would appear to be advisable not to breed from animals with this condition. Bell (2010) suggested the assignation and use of breeding values when tackling suspected polygenetic disorders. These take account of the incidence of the disease in the individual and close relatives. In developing breeding strategies to tackle particular genetic diseases it is important to take account of other diseases also and to avoid further inbreeding (eg where necessary, by crossing with other breeds) that may result in new genetic risks. .

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

Pulmonic stenosis (PS) is a common congenital (present at birth), hereditary heart abnormality of dogs (Patterson 1989). Bulldogs are particularly predisposed to PS and it is in this breed that it occurs most commonly (Buchanan 2001). When severe it can lead to exercise intolerance, right-sided heart failure and premature death.

The heart is a four-chambered pump which is divided into left and right sides. Each side has two chambers: blood enters the thin-walled upper chamber (atrium). It then flows into the larger, lower chamber (ventricle). The ventricles have thick muscular walls. Between the atria and the ventricles are valves that prevent blood flowing backwards. On contraction, blood flows from the ventricles into the major blood vessels. There are also valves at the junction of the ventricles and these blood vessels that prevent backward flow.

The right side of the heart receives blood from the whole of the body, other than the lungs, via the major vein - the vena cava. The blood accumulates in the right atrium and during each heart beat it is sucked past the tricuspid valve into the right ventricle and then as the right ventricle contracts (squeezes) it is pushed through the pulmonary valves into the pulmonary arteries and so to the lungs to take up oxygen.

The left side of the heart receives this oxygenated blood back from the lungs, via the pulmonary veins. The blood accumulates in the left atrium and during each heart beat, it is sucked past the mitral valve into the left ventricle. Then, as the left ventricle contracts, the blood is pushed through the aortic valves into the aorta and on into other the major arteries which convey it around the body to perform all the functions of blood circulation - such as delivering oxygen and nutrients and sharing heat and metabolic products throughout the body.

The phase when the heart is contracting to squeeze forward the blood inside its cavities is called systole. The phase between heart beats when it is relaxing and filling is called diastole.

Stenosis means narrowing and pulmonic stenosis refers to narrowing of the pulmonary blood flow from the right ventricle, which obstructs the flow of blood leaving the heart. In dogs stenosis can occur at one of three places (Rishniw 2004):

• Supra-valvular (above (downstream) of the heart valve): ie in the pulmonary artery.
• Valvular: at the level of the pulmonary heart valves.  There are two forms of this: type A is caused by abnormal formation (dysplasia) of the pulmonary valves themselves in which the leaves (flaps) that closethe valve are  partially fused. Type B occurs when the base of the heart valves – the pulmonary valve annulus - is malformed and small (hypoplasia).
• Sub-valvular (below (upstream) of the heart valve): the narrowing is within the right ventricle. This may be due to thickening of the heart muscle.

Type A stenosis at the valvular level is the commonest form in most types of dogs (Ryan no year), however in English bulldogs another form of PS is commonly seen (Buchanan 2001). This is due to an abnormality of the left coronary artery, which is one of the first arteries to branch off from the aorta and which is one of two to supply blood to the heart muscle itself. Instead of arising directly from the aorta, in affected dogs, the left coronary artery arises from the other coronary artery – the right - and then passes around the junction of the right ventricle and the pulmonary artery, before supplying the left side of the heart with blood. The effect of this is that the left coronary artery is wrapped around the right ventricular outflow tract, which is entrapped and narrowed near the level of the pulmonary valve and it is this that causes a stenosis (Buchanan 1990, et al 2002, Kittleson et al 1992), classified as an R2A anomaly. Buchanan (2001) suggested that this may be the commonest form of PS in English Bulldogs.

If the PS is severe enough to cause it, the right ventricular wall hypertrophies (thickens) to pump blood past the narrowing. This ventricular wall hypertrophy causes secondary heart problems. The severity of PS is graded by assessment of the degree of right ventricular wall hypertrophy (via ultrasonography) and by measuring the blood pressure gradient across the stenosis (measured via a catheter inside the vessel or via Doppler ultrasonography) (Rishniw 2004, Stafford-Johnson 2006). The grades are:

• Mild – with pressure gradients of less than 40 to 50 mmHg and absence of right ventricular hypertrophy (Rishniw 2004, Stafford-Johnson 2006).
• Moderate – with pressure gradients between 40 to 80 mmHg and mild to moderate right ventricular hypertrophy (Rishniw 2004, Stafford-Johnson 2006).
• Severe – with pressure gradients greater than 80 mmHg and moderate to marked concentric right ventricular hypertrophy (Stafford-Johnson 2006).

The clinical course of the disease and the treatment options depend on the grade of the PS. Dogs with mild to moderate PS usually require no intervention and are likely to lead normal lives (Stafford-Johnson 2006). Occasionally however some dogs affected in this way will die suddenly, without prior signs and others progress to right-sided heart failure (as discussed below). Severe cases, particularly those with concomitant tricuspid valve incompetence (leaking tricuspid valve), may progress to right-sided heart failure (Fingland et al 1986, Stafford-Johnson 2006). In a study of 43 dogs with PS graded as severe, 79% had clinical signs of disease at time of referral (Stafford-Johnson & Martin 2004). It is also common for other congenital heart defects to be present concurrently. In about 50% of severe PS cases there is also an atrial septal defect (a hole connecting the two atria of the heart) (Rishniw 2004).

Signs of right-sided heart failure include fatigue, progressive exercise intolerance(which usually shows as breathlessness on exercise). Syncope (sudden collapse and fainting) can occur in some cases, probably because of insufficient blood supply to the brain (Hall et al 2003). Ascites (fluid accumulation in the abdominal cavity) and distension of the jugular veins can occur because the inefficient pumping of the right side of the heart leads to damming back of blood and increased pressure in the venous system. Dogs with severe PS are also prone to heart arrhythmias - irregular heartbeats - which may lead to syncope and weakness. Sudden death can occur at any time (Hall et al 2003) and the risk of death increases with increased pressure gradient above and below the stenosis ie with the severity of the PS (Stafford-Johnson et al 2004).

English bulldogs with PS, but without heart failure, will be likely to appear normal to their owners and to not have any welfare problems associated with the PS. However, examination with a stethoscope often reveals a heart murmur in these cases and this is commonly the way in which the disease is first detected, when puppies are taken for their first vaccinations or check up. Heart murmurs are caused by abnormally turbulent blood flow. With PS the murmur is usually described as ‘harsh’ and is best heard with the stethoscope positioned well forward on the thorax (chest) near the sternum (Darke 1989, Hall et al 2003).

Treatment is generally not necessary in mild to moderate cases. The point at which it becomes necessary is somewhat controversial – currently most cardiologists recommend treatment for all those cases graded severe. Treatment of valvular dysplasia usually consists of balloon valvoplasty which involves passing a catheter through a peripheral artery to the place of stenosis and then inflating it at that point to stretch the narrowed area. This is often successful at preventing or improving clinical signs of disease in affected dogs (Stafford Johnson & Martin 2004, Stafford Johnson 2006, Ristic et al 2001).

Treatment for the coronary vessel anomaly is more difficult and bulldogs with this type of PS have had a poorer outlook. However, however, a recent study has suggested that “conservative” balloon valvuloplasty can be safe and can improve clinical signs and quality of life (Fonfara et al 2010).

Dogs in right-sided heart failure require medication to control the consequences of the condition. The success of the treatment depends on its severity.

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2. Intensity of welfare impact

Mild PS may have no, or only slight, effects on welfare. However, where the stenosis is more severe, some dogs develop right-sided heart failure (Stafford-Johnson 2006). and affected dogs lack energy, feel unwell and are unable to exercise properly. They may also feel breathless, and may faint and collapse. The disease can significantly affect quality of life and may lead to death through heart failure.

Investigations and treatments for PS may have adverse welfare effects associated with travel to and from veterinary practices, surgical treatment hospitalisation, and with side effects of the medication given to treat the condition.

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3. Duration of welfare impact

The time course of the pulmonic stenosis can be long (months or years) from the development of heart failure to death, depending on the severity of heart failure and the extent to which it may respond to surgical or medical therapy.

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4. Number of animals affected

In a large survey of dogs in the USA, English bulldogs were found to have the highest breed prevalence of pulmonic stenosis , it being 19 times more common in the breed than is normally seen in dogs. However, a far as we are aware, there are no data available on the proportion of English bulldogs affected. Male bulldogs are more likely to have the problem than females – 80% of affected dogs were male (Buchanan 1992). PS is the commonest congenital heart defect in the breed but it is also predisposed to another, involving the ventricular septum (Buchanan 1992).

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5. Diagnosis

A ‘harsh’ heart murmur in any young English bulldog is suggestive of a heart defect, particularly PS, as this is the commonest congenital heart defect in the breed (Buchanan 2001). Confirmation is usually made using colour-flow Doppler ultrasonography.

In dogs with heart failure other diagnostic tests, including information from a full physical examination, ECG (electrocardiogram) and possibly chest and abdominal radiographs (x-rays) may be used to rule out other possible causes and to assess the stage of disease and to plan treatment options.

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6. Genetics

PS has been shown to be hereditary in beagles (Patterson 1984) and is thought to be hereditary in other breeds also including the English bulldog (Darke 1989, Ryan no date) and it is thought to be a polygenic threshold trait in these cases (Patterson 1989). That is, it is thought that multiple genes are involved. The severity of the defect and its disease consequences are likely to be directly related to the abnormal genetic burden in each individual (Patterson 1989).

The genes involved have not been identified and it is not known why males are more at risk than females.

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7. How do you know if an animal is a carrier or likely to become affected?

It is not known whether animals can carry the genes that cause pulmonic stenosis without developing the disease themselves, although this seems likely, and there is no way to detect such carriers at present.

Dogs with the disease should not be used for breeding, and matings which result in affected offspring should not be repeated. All English bulldog puppies should be examined by a veterinary surgeon prior to purchase as purchase of puppies with a heart murmur may facilitate perpetuation of the problem. Being free of a murmur at time of purchase does not guarantee absence of PS but it makes it far less likely.

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8. Methods and prospects for elimination of the problem

As far as we are aware, there are no breeding programmes aimed at reducing the prevalence of, or eradicating, pulmonic stenosis from the English bulldog breed.

In tackling suspected polygenic disorders, Bell (2010) suggested the assignment and use of estimated breeding values (EBV). An EBV is a “numerical prediction of the relative genetic value of a particular dog” based on pedigree, health status and physical characteristics of the dog itself and of its relatives. Healthy individuals with healthy relatives have the greatest chance of carrying a low genetic load for the condition (Bell 2010). This EBV approach can also be used to try and eliminate several hereditary diseases within a breed simultaneously. Unfortunately, English bulldogs are predisposed to a number of hereditary conditions which significantly affect their health.

This approach (using EBVs) has proved successful in tackling some other conditions eg in the reduction of epilepsy in the Belgian Tervuren (Oberbauer 2005) and may be a promising way to eliminate this condition from the English bulldog breed although it may take many generations. However, opinions differ as to whether it is ethically acceptable to breed animals whose welfare is likely to be compromised. 

As with other polygenic disorders progress in eliminating PS would be likely to be facilitated by identifying the genes involved.

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section

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10. References

Bell JS (2010) Genetic Testing and Genetic Counseling in Pet and Breeding Dogs. World Small Animal Veterinary Association World Congress Proceedings

Buchanan JW (1990) Pulmonic stenosis caused by single coronary artery in dogs: Four cases (1965-1984). Journal of American Veterinary Medical Association 196: 115-120

Buchanan JW (1992) Causes and prevalence of cardiovascular disease. In Kirk RW, Bonagura JD (eds) Current Veterinary Therapy XI. WB Saunders: Philadephia USA pp647–655

Buchanan JW (2001) Pathogenesis of single right coronary artery and pulmonic stenosis in English Bulldogs. Journal of American Veterinary Medical Association 15: 101-104

Buchanan JW, Anderson JH and WhiteRI (2002) The 1st balloon valvuloplasty: An historical note. Journal of Veterinary Internal Medicine 16: 116-117

Fingland RB, Bonagura JD and Myer CW (1986) Pulmonic stenosis in the dog: 29 cases (1975-1984). Journal of American Veterinary Medicine Association 189: 218-226

Darke PGG (1989) Congenital heart disease in dogs and cats. Journal of Small Animal Practice 30: 599-607

Fonfara S, Martinez Pereira Y, Swift S, Copeland H, Lopez-Alvarez J, Summerfield N, Cripps P and Dukes-McEwan J (2010) Balloon valvuloplasty for treatment of pulmonic stenosis in English Bulldogs with an aberrant coronary artery. Journal of Veterinary Internal Medicine 24: 354-9

Hall EJ, Murphy KF and Darke PGG (2003) Pulmonic stenosis In: Notes on Canine Internal Medicine pp 221-223. Blackwell Publishing: Oxford, UK

Kittleson M, Thomas W, Loyer C and Kienle R (1992) Single coronary artery (type R2A). Journal of Veterinary Internal Medicine 6: 250-251

Oberbauer A (2005) Recent Progress on the Genetics of Canine Epilepsy and Addison's Disease. Tufts' Canine and Feline Breeding and Genetics Conference, 2005

Patterson DF (1984) Two hereditary forms of ventricular outflow obstruction in the dog: Pulmonary valve dysplasia and discrete subaortic stenosis. Nora JJ and Takao A Eds Congenital Heart Disease: Causes and Processes. Futura Publishing Co: Mount Kisco, USA pp 43-64

Patterson DF (1989) Hereditary congenital heart defects in dogs. Journal of Small Animal Practice 30: 153-165

Rishniw M (2004) Pulmonic Stenosis. VIN Associate. http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1239. Accessed 25.4.11.

Ristic JME, Marin CJ, Baines EA and Herrtage ME (2001) Congenital pulmonic stenosis: a retrospective study of 24 cases seen between 1990-1999. Journal of Veterinary Cardiology 3: 13-19

Ryan M no year Understanding Canine Pulmonic Stenosis – client leaflet. University of Pennsylvannia, School of Veterinary Medicine: Philadelphia, USA

Stafford-Johnson M (2006) Decision making in suspected congenital heart disease in dogs and cats. In Practice 28: 538-543

Stafford-Johnson M and Martin M (2004) Results of balloon valvuloplasty in 40 dogs with pulmonic stenosis. Journal of Small Animal Practice 45: 148–153

Stafford-Johnson M, Martin M, Edwards D, French A and Henley W (2004) Pulmonic stenosis in dogs: Balloon dilation improves clinical outcome. Journal of Veterinary Internal Medicine 18: 656-662

© UFAW 2011

Credit for main photo above:

By Asmadeus (Own work) [Public domain], via Wikimedia Commons