Sub Aortic Stenosis
Dilated Cardio-Myopathy

HEART

Canine Dilated Cardiomyopathy (DCM)

A condition that affects both dogs and humans.

Dilated cardiomyopathy ( DCM) is a condition that affects both humans and dogs and is characterised by left sided or four chamber dilation of the heart with impaired systolic function.

Dr. Jo Dukes-McEwan is a Senior Lecturer in Veterinary Cardiology and a clinical cardiologist based in the Small Animal Hospital within the University of Liverpool. Jo has been actively involved in investigating the genetics of DCM since 1996 and gained her PhD in this area following funding by the Kennel Club Charitable Trust. Since then Jo has been combining a busy clinical career with research and her recent studies funded by the British Heart Foundation have focussed on identifying genetic risk factors for DCM in extended affected pedigrees of Newfoundland dogs. Her work has led to the identification of a clear  familial basis to the disease. Longitudinal studies in affected families using serial Doppler echocardiography documented a long pre-clinical stage with gradual impairment in contractibility and left ventricular enlargement and progressive rounding. Pedigree analysis of these families has been consistent with an autosomal dominant mode of inheritance, although other factors, possibly such as nutrition, may also influence the age of onset and rate of progression.

Since the dog genome has been sequenced it is becoming increasingly important to utilise information gained in the dog about diseases to provide insights into counterpart conditions in humans, and of course vice-versa. These types of studies are called comparative genomics. Jo has been examining the possible involvement of genes encoding cytoskeletal proteins in canine DCM that  were originally identified in human DCM.

As yet Jo has not identified the cause of DCM in Newfoundland dogs but is hopeful that new molecular and genetic studies will be successful. Jo is delighted that the UK DNA Archive is now including DNA samples fromdogs and cats with various cardiac diseases . She recently said” The Archive will be a tremendous resource for researchers in future years. Collecting large numbers of samples with good clinical phenotype data can take many years. If clinicians from all over the UK collect this data and submit DNA to the Archive, this will form a firm foundation for future geneticresearch of cardiac diseases in our companion animals”

 


DCM
DILATED CARDIO-MYOPATHY

Understanding the Results of Heart Testing

 

Dr. Jo Dukes McEwan BVMS, MVM, PhD, DVC, MRCVS

RCVS recognised Specialist in Veterinary Cardiology

University of Edinburgh Hospital for Small Animals,

Easter Bush Veterinary Centre,

Easter Bush, Nr. Roslin, MIDLOTHIAN EH25 9RG.

 

Both the original and the new heart test certificates have led to some confusion in people’s minds because of the difficulty in understanding the results.  The new certificates have solved problems in having separate copies for the owner, the dog’s vet, the cardiologist and research collation, and they are less onerous to fill out.

 The heart test result is given as the Grade of any heart murmur detected by the cardiologist. Murmurs are graded as 1 to 6 out of 6. Very quiet murmurs are graded 1/6 and the loudest murmur is a 6/6. The Veterinary Cardiovascular Society have established some guidelines for UK cardiologists to ensure that grading of murmurs detected with a stethoscope is as consistent as possible between cardiologists.

 If no heart murmur is detected, then a grade 0/6 can be inferred.  The results of the echo-Doppler examination (if done) should be checked before it can be assumed that the dog is normal.

HEART MURMURS MAY OCCUR FOR VARIOUS REASONS

 Although the detection of a heart murmur is abnormal in Newfoundlands, it does not tell the cardiologist or the owner what the underlying problem is due to. An experienced cardiologist may be able to make an educated guess based on the characteristics of the heart murmur and the point of maximal intensity on the chest wall, but echo-Doppler is required to confirm the reason for the murmur.  Heart murmurs may be due to:

 1.    Narrowed valves (offering increased resistance to flow, so flow velocity (speed) has to increase to get through the obstruction. Think of a narrow part of a river compared to a wider part. The flow is fast and turbulent in the narrow part. This results in a heart murmur). Examples are aortic or sub-aortic stenosis or pulmonic stenosis.

 2.    Leaky valves. As a leak of blood jets through the incompetent valve, it results in a murmur, since the abnormal flow (regurgitation) is fast and turbulent.  Most murmurs associated with leaky valves are due to mitral or tricuspid regurgitation. 

3. Abnormal shunts. If there is a defect in the heart, such as a ventricular septal defect (VSD: A hole between the left and right ventricles) or a Patent Duct Arteriousus (PDA), blood passes through these areas resulting in a heart murmour.

Obstruction to blood flow (narrowd or leaky valve)

 

 

 

 

 

Turbulent, high velocity bloodflow after the obstruction

 

Normal laminar bloodflow

Figure 1.

Diagram illustrating how blood flow passing a narrowed area (e.g. stenotic or leaky valve) results in change from normal (laminar) flow to turbulent flow.  The high velocity turbulent flow in the heart may result in an audible heart murmur.

Sub-aortic stenosis is the main congenital heart disease of concern in Newfoundland dogs.  Confirmation of diagnosis by echo-Doppler is based on a Doppler recording of a peak aortic velocity exceeding 1.7 metres per second in a relaxed dog. The blood flow through the aortic valve is normally much less than 1.7 m/s. Increased velocity is associated with increased turbulence of blood. These are both factors in creating a heart murmur. The abnormal flow is a consequence of a narrowed (stenotic) area affecting the aortic valve or caused by a fibrous ridge below the valve.

There are other congenital heart diseases occasionally seen in Newfoundlands, which may be associated with a murmur, or in some cases (such as severe tricuspid valve dysplasia) no murmur is detected.   Murmurs may be continuous such as in patent ductus arteriosus (PDA).

In DILATED CARDIOMYOPATHY (DCM), there is no primary defect affecting the heart valves or flow of blood through the heart, and so NO heart murmur is often recorded (0/6).  This must NOT be interpreted as the dog having a normal heart. The heart test result has to be interpreted based on the echo-Doppler result. Often, an abnormal heart rhythm is detected, with abnormal beats (“ectopics”) or atrial fibrillation – before any murmur.  Later in the course of DCM, since the chambers of the heart become massively dilated, the mitral valve annulus (the “scaffolding” supporting the leaflets of the mitral valve) becomes stretched, and this can have the consequence of mitral regurgitation – which is then detected as a heart murmur. In DCM, therefore, in the early stages, there may be NO abnormalities listening through a stethoscope but as the disease develops, murmurs will develop, although rarely higher than grade 2/6.  Other abnormal findings can be detected with a stethoscope in dogs with heart failure, prior to successful treatment. We can hear “gallops” which are due to the stiffened ventricles filling with blood. Gallops are always abnormal. It is satisfying to monitor these during treatment. Once heart failure is controlled, the gallops resolve.  

Figure 2.

Diagram illustrating a normal heart (left) and the changes seen with DCM (right). The four chambers of the heart are labelled; right atrium (RA), right ventricle (RV), left atrium (LA) and left ventricle (LV). The mitral valve is situated between the left atrium and left ventricle. Normally, during the relaxed stage of the heart cycle (diastole), blood flows from the left atrium to the left ventricle through an open mitral valve. During ventricular contraction (systole), blood flows out of the LV into the aorta and the mitral valve closes (large arrow, left). In DCM (right), the chambers of the heart are dilated and the walls are thin. The mitral valve annulus is “stretched”, so during ventricular contraction, as well as normal blood flow into the aorta, some flows retrograde across the valve leafets into the left atrium, giving rise to turbulent blood flow which may be heard as an audible heart murmur.  This explains why some dogs with DCM have a heart murmur graded on heart testing.   

THE GRADE OF A HEART MURMUR DOES NOT NECESSARILY CORRELATE WITH THE SEVERITY OF HEART DISEASE 

Although the grade of heart murmur correlates with how severe the disease is in Aortic stenosis, in other heart conditions, such as PDA, there is no correlation. In severe tricuspid dysplasia, there may be NO murmur detected.  In DCM, the dog may have severe disease and severe heart failure but very low-grade murmurs or no heart murmur.

OTHER FACTORS INFLUENCE HEART MURMURS

 In SAS, there may be NO murmur in a young pup. As the pup grows and the heart grows, the abnormality below the valve remains constant, so it becomes proportionately worse with ageing. This is the reason that dogs should be over 12 months old for the results of official heart testing to be recorded or published.  Although it is sensible to get pups checked, they must be re-examined at over 12 months old.  There is a possibility that SAS does become more severe up until 24 months of age, but then remains reasonably constant.

We have shown that some Newfoundlands, being broad-chested, possibly over-weight, and tending to pant, have NO audible heart murmur.

There is evidence of SAS on echo-Doppler. This shows that the sensitivity of heart testing by the stethoscope alone is insufficient to detect all cases of SAS (although it will certainly detect the more severe cases). This is the reason why dogs used at stud should be echo-Dopplered for SAS. Stud dogs are potentially responsible for many more progeny than bitches. 

Dogs which had a heart murmur detected at 12 months old will mature and may put on a lot of weight and then the murmur becomes undetectable. Similarly, dogs with no heart murmur detected may lose a lot of weight, and then one becomes apparent.

 In DCM there may be no murmur, despite the fact mitral regurgitation is confirmed on echo-Doppler. This is because the contractility of the heart may be so reduced that the heart muscle does not generate sufficient force for the jet of blood (of mitral regurgitation) to be fast enough to result in an audible heart murmur.

ECHO-DOPPLER SCREENING FOR DCM

DCM is an acquired heart disease. The dog is not born with it. It gradually develops after adult-hood and the average age of symptoms developing is 8 years old.  If we scan an affected dog about 12 – 24 months prior to the development of symptoms of breathlessness, exercise intolerance or coughing, the classical features of DCM are evident on echocardiography. These features are:

·        Dilated, rounded left ventricle.

·        Walls of the ventricles appear thin.

·        Severely reduced contractility of the left ventricle. The fractional shortening is an easy-to-obtain indicator of contractility. In DCM, it is less than 22%. 

·        Dilated left atrium

·        May have arrhythmias such as atrial fibrillation detected on the ECG through the scan.

Because these dogs show no symptoms, we call this OCCULT DCM. Even if no heart murmur is detected (0/6), these dogs are ABNORMAL and have significant heart disease. This will be shown in the echo-Doppler section of the heart test form. It is not possible to predict how rapidly the disease will progress to eventually result in symptoms. In some dogs, it may be rapid and in others, it may take over two or more years. The older a dog is at the time of diagnosis of occult DCM, the more slow the progression tends to be. The progression tends to be faster in dogs compared with bitches.

Prior to this, we may identify other echo-Doppler abnormalities in Newfoundlands. These are:

·        LEFT VENTRICULAR ENLARGEMENT (LVE)

Only occasional Newfies have this abnormality, but they do progress to develop more classical DCM within 12 – 18 months, although it is often longer before they show symptoms.  Male dogs with a LV dimension of over 55 millimetres and bitches of over 50 mm are abnormal.  These dogs have a normal fractional shortening.

·        DEPRESSED FRACTIONAL SHORTENING (dFS)

These Newfies have a normal elliptical shape to the left ventricle and it is not dilated. There only abnormality is a very low fractional shortening measurement (and other parameters of contractility also confirm the pumping ability of the LV is impaired). Fractional shortening less than 18% is very low. Between 18 and 20% may be equivocal.

 In the four years or so that we have been monitoring Newfies with severe dFS (less than 18%), only 5 out of 29 dogs developed DCM. Most of the dogs have remained similar on repeat scanning.  There are still unanswered questions about this group:

-         Will these dogs go on to develop DCM in the future?

-         Do they have a limited manifestation of DCM which will not progress?

-         Is it a normal variation? (This is unlikely, since we do not see this in Newfies where there is no positive family history of DCM).

-         Only by continuing the serial scans through the dogs’ lives will we be able to answer these questions.

 A note will be made in the heart test forms if these EQUIVOCAL findings are identified.

SERIAL SCANS ARE REQUIRED TO EXCLUDE DCM

It is apparent that one normal scan when the dog is young (e.g. 18 months old) does NOT mean that he/she will remain normal.  We would strongly advise that all stud dogs are repeat scanned every 2 years to rule out the gradual development of DCM. In Newfie families where there have been a number of cases of DCM, all breeding stock should be scanned serially.  Since we believe that DCM is inherited as an autosomal dominant trait, only one parent needs to carry one copy of the gene for up to 50% of its progeny to also be affected.

DCM: THE GENETIC STUDIES

It is vital that I know what happens to dogs with echo-Doppler equivocal findings, for the genetic analysis. Although I have a DNA sample from most of the dogs I have scanned, I need to be certain that dogs are definitely normal or abnormal by the end of their lives. If we obtain this information, by serial scans or by examining hearts obtained at post-mortems, it will help the genetic studies – and I am extremely grateful to all Newfie owners and breeders who have allowed the serial scans. With this confirmed information, the genetic studies should result in a blood test for DCM which can be used in young dogs, which will identify dogs at risk for developing DCM. 

 Jo Dukes McEwan

 August 2000



 

 

UPDATE ON DCM & LUPA STUDY

With thanks to Hannah Copeland
Cardiology Department
Small Animal Teaching Hospuital
Liverpool University

Dilated Cardiomyopathy in Newfoundlands


Dilated cardiomyopathy (DCM) is one of the most common heart diseases of all breeds of dogs. As the name suggests, it is characterised by progressive thinning of the heart muscle, and dilation of the heart chambers, with concurrent severely impaired pumping ability of the muscle (impaired contractility). DCM was first reported in Newfoundlands in 1970, and we now know it can be an inherited disease in this breed.
Dilated cardiomyopathy is a particularly difficult disease to control in dogs as it is an adult-onset disease. Studies have shown that Newfoundlands in particular can have ‘occult’ DCM (i.e. they have the disease but do not show clinical signs) for many years before developing signs, and therefore may have already been bred many times before anyone becomes aware that they have heart disease. We are currently trying to collect and analyse DNA samples from Newfoundlands in the hope of identifying the gene(s) responsible for the disease and eventually developing a genetic test, which could identify dogs at risk from a very young age.

The normal function of the heart is shown on the diagram. Blood low in oxygen returns from the body to the right atrium and from there to the right ventricle. As the heart contracts, the right ventricle pumps the blood to the lungs via the pulmonary artery, where the blood picks up oxygen. Oxygen-rich blood returns from the lungs, via the pulmonary veins, to the left atrium and then the left ventricle, and the left ventricle pumps the blood around the whole body via the aorta. Therefore blood returning from the body has to pass through the heart twice before it can take oxygen back to the tissues. As the left ventricle has much more work to do, it is usually larger and more well-muscled than the right ventricle.

 

In order to be definitively diagnosed with DCM, a dog must have an ultrasound examination of the heart (echocardiography). The diagnosis is made based on measurements of the size and contractility of the heart, and the exclusion of any other heart disease which might produce similar signs. Dogs start to show clinical signs when the heart’s contractility is so poor that it is unable to pump blood around the body efficiently. Initial signs may just be that the dog is less able or willing to exercise, as their tissues are not receiving the blood and oxygen they need to work harder during exercise.


Dilated cardiomyopathy will eventually progress to heart failure. This is the point at which the heart’s ability to maintain a ‘steady state’ in the body is overwhelmed. If the heart is unable to pump efficiently, it is unable to move blood returning from the body or lungs, and therefore blood backs up in the vessels. Fluid is constantly moving between the blood vessels and the surrounding tissues, and therefore an increase in pressure in the vessels (due to back up of blood) pushes more fluid in to the tissues. Heart failure is usually classified as left-sided, right-sided or both. Left-sided failure occurs when the left ventricle fails to move blood returning to it from the lungs. Right-sided failure occurs when the right ventricle fails to move blood returning to it from the body.


A build up of fluid in the lungs is known as pulmonary oedema. The fluid reduces the amount of oxygen that can pass from the lungs in to the blood stream. Dogs with pulmonary oedema often show breathlessness (dyspnoea) and exercise intolerance due to poor oxygenation. They often will also cough as the body’s reflexes try to clear the fluid from the airways. A build up of fluid in the abdomen (associated with right-sided failure) is known as ascites, and can result in a pot-bellied appearance.

 

 

A build up of fluid in the lungs is known as pulmonary oedema. The fluid reduces the amount of oxygen that can pass from the lungs in to the blood stream. Dogs with pulmonary oedema often show breathlessness (dyspnoea) and exercise intolerance due to poor oxygenation. They often will also cough as the body’s reflexes try to clear the fluid from the airways. A build up of fluid in the abdomen (associated with right-sided failure) is known as ascites, and can result in a pot-bellied appearance.


Drugs can be used to alleviate the symptoms of heart failure, and to try and reverse some of the changes in the heart itself. However, nothing is curative, and we also do not know of any drugs which can prolong the symptom-free life of Newfoundlands which have occult DCM, although some groups of drugs (ACE inhibitors) can achieve this in humans and Dobermann dogs with similar disease. A dog with heart failure may be on any or all of the following drugs:


         Diuretic (e.g. Frusemide, Prilactone). These drugs increase the amount of fluid lost in the urine and therefore help to reduce build-up of fluid in the tissues


         ACE Inhibitor (e.g. Fortekor, Vasotop, Enacard). These drugs counteract the adverse hormonal effects that heart failure has on the body


         Anti-arrhythmics (e.g. Diltiazem, Digoxin). The significant stretch and damage of the heart muscle can result in arrhythmias with very fast heart rates, such as atrial fibrillation. These drugs aim to slow the heart rate.


         Vetmedin. This drug helps to improve the pumping ability of the heart


Newfoundlands in heart failure may also benefit from nutritional supplements. Deficiency of taurine has been associated with DCM, and therefore dogs can be supplemented with taurine. Omega-3 fatty acids have also been shown to be beneficial to dogs in heart failure, and can be found in fish oils, or supplements at the pharmacy or from your vet.


A European consortium of vets and geneticists, known as LUPA, are currently researching DCM in the Newfoundland, and other breeds known to have an inherited form of DCM. Other genetic diseases are also being investigated, and it is hoped we will be able to identify genetic markers for these diseases and eventually develop genetic tests. The information obtained will also hopefully be used in human medicine to identify the genes responsible for these diseases in people. More details on the project as a whole can be found at www.eurolupa.org

In the UK, LUPA DCM research is being carried out at the University of Liverpool by Hannah Copeland, a veterinary research assistant, and Dr Jo Dukes-McEwan, a European Specialist in cardiology. Their aim is to collect DNA samples from Newfoundlands with DCM, and healthy Newfoundlands, to be used in the study. The DNA of these dogs will be compared to see if there are consistent differences between dogs with DCM and healthy dogs, and therefore potentially identify the gene(s) involved in DCM.


Identifying truly healthy Newfoundlands can be difficult, as DCM can have an occult phase of many years before any signs become apparent. The researchers are therefore carrying out FREE screening of Newfoundlands AGED SEVEN OR OLDER. Screening includes:


         a full clinical examination and auscultation


         a full echo Doppler (heart scan) examination


         a screening blood sample for older dogs


A copy of the dog’s pedigree is required, as dogs going on to be included in the study MUST be unrelated at parental level, and ideally grand-parental level. For more information about the study and getting involved in screening, please contact Hannah Copeland (details below).
DNA samples and pedigrees from Newfoundlands that have been diagnosed with DCM are also needed for the project. For information on how to submit DNA samples, please contact Hannah Copeland (details below).


sath@liv.ac.uk
0151 795 6100
University of Liverpool
Small Animal Teaching Hospital
Leahurst
Chester High Road,
Neston
Wirral, CH6 7TE

 

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