To wrap up the month of February, which celebrates American Heart Month and Heart Awareness Month, The Meowing Vet is back with yet another cardiac-focused veterinary article to bring pet owner awareness to Canine Degenerative Mitral Valve Disease. 💔

 

Degenerative mitral valve disease is the most common form of heart disease in dogs as a whole. It can lead to congestive heart failure (CHF) and is particularly a concern in small breed dog breeds. Earlier in the month, we posted an article by boarded veterinary cardiologist Dr. Michael Aherne on the ins-and-outs of congestive heart failure (CHF) in dogs and cats. To follow up on his previous article, Dr. Aherne joins us yet again as guest writer to provide expert information on degenerative valve diseases as a whole, focusing on mitral valve disease while also incorporating information on degeneration of the tricuspid valve. If you haven’t already been “introduced” to Dr. Aherne in his previous article (which we highly recommend you read), say hello now! Dr. Michael Aherne, MVB (Hons 1), GradDipVetStud, MS, MANZCVS (Small Animal Surgery), DACVIM (Cardiology) is a boarded veterinary cardiologist who is eager to educate pet owners on common cardiac conditions most likely to be of concern to dogs and cats. So let’s get started!

– Maranda Elswick, DVM

Read Dr. Aherne’s article below…

Introduction

Degenerative valve disease is the most common heart disease identified in dogs. Though dogs of any size may be affected, the disease is most commonly seen in small breed dogs with the reported incidence of the disease over the lifetime of certain small breeds of dogs being nearly 100%. Cats are rarely affected by degenerative valve disease and most cases of feline heart disease are due to cardiomyopathies (diseases of the heart muscle). In dogs, degenerative valve disease is an age-related disease that primarily affects the mitral valve, which is the main valve on the left side of the heart located between the left atrium and left ventricle. (Need to brush up on your knowledge of the anatomy of the heart? Click here for a refresher.) However, any of the heart valves may be affected, and in many cases more than one valve will have evidence of degeneration. The tricuspid valve, which sits on the right side of the heart between the right atrium and right ventricle, is the second most commonly affected valve. Typically, degenerative disease is a slowly progressive disease, and many dogs do not develop clinical signs as a result of their disease. However, in some dogs the disease may progress to the point that left-sided congestive heart failure (CHF) may develop, and medical or surgical therapy will be required. Since the mitral valve is most commonly affected, it is often referred to as mitral valve disease or degenerative mitral valve disease. However, there are a multitude of different names and acronyms that have been used to describe the same disease in dogs as listed below:

• Degenerative valve disease (DVD)
• Degenerative mitral valve disease (DMVD)
• Mitral valve disease/degeneration (MVD)
• Myxomatous mitral valve disease (MMVD)
• Myxomatous valvular degeneration
• Chronic valvular disease/degeneration (CVD)
• Endocardiosis

 

Pathophysiology

The exact underlying cause for development of degenerative valve disease in dogs is unknown and is the subject of much research. Any breed of dog may be affected; however, some small breeds of dog have a very high risk for developing the condition and within these breeds there appears to be a strongly heritable component. The breed most commonly associated with development of degenerative valve disease is the Cavalier King Charles Spaniel. Below is a list of some of the breeds more commonly affected by degenerative valve disease.

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  Cavalier King Charles Spaniels are the most common dog breed to acquire degenerative mitral valve disease.

  Cavalier King Charles Spaniel

• Shih Tzu
• Dachshund
• Chihuahua
• Maltese Terrier
• Pomeranian
• Yorkshire Terrier
• Miniature and Toy Poodles
• Miniature Schnauzer
• Cocker Spaniel
• Shetland Sheepdog
• West High White Terrier
• Mixed-breed dogs

 

The mitral valve comprises of two thin leaflets made of fibrous tissue that, at their base, are anchored to the wall of the heart in a ring-like structure known as the mitral annulus. The loose portions of the mitral leaflets are attached to the papillary muscles within the left ventricle by thin, rope-like fibers called chordae tendineae. When the valve leaflets are closed, the whole structure somewhat resembles a parachute, with the closed leaflets resembling the main body of the parachute and the chordae tendineae resembling the strings that attach to it. The function of the chordae tendineae is to prevent the mitral valve leaflets from bending back too far in the wrong direction. In a normal animal, when the mitral valve is closed during contraction of the heart, it prevents any blood in the left ventricle from flowing back the wrong direction (i.e. into the left ventricle). (Click here for a detailed explanation of heart valve function.) The remaining valves all function in a similar manner, though the size, shape, leaflet number and location of the other valves will differ. The timing of valve leaflet closure also differs between pairs of valves: the mitral and tricuspid valve are closed during the contraction period of the heart (called systole) to prevent backflow of blood from the ventricles into the atria, while the aortic and pulmonic valves are closed during relaxation period of the heart (called diastole) to prevent backflow of blood from the aorta and pulmonary artery into the left and right ventricles respectively.

In a dog with degenerative valve disease, the mitral valve leaflet becomes thickened and somewhat nodular in appearance. This is called myxomatous degeneration. In addition, the chordae tendineae also become stretched, and some chordae may rupture. This stretching or rupture of chordae tendineae causes portions of the mitral valve leaflets to prolapse or bow back into the left atrium. As a result of incomplete closure of the valve leaflets due to thickening and/or prolapse of portions of the valve leaflets blood is able to leak back from the left ventricle into the left atrium when the heart contracts (systole) in a high-velocity jet called mitral regurgitation (MR). This high-velocity jet of mitral regurgitation creates turbulence which causes an abnormal sound called a heart murmur. (How does a heart murmur develop? Click here to find out the deets.) In dogs, the mitral leaflet closest to the interventricular septum of the left ventricle (called the anterior mitral leaflet) is frequently more severely affected than the leaflet attached to the free-wall of the left ventricle (called the posterior mitral leaflet) though both leaflets can be affected. As a result, the majority of heart murmurs due to mitral valve degeneration in dogs are angled towards the free-wall of the left atrium, and thus, are directed towards the left side of the dog’s chest near the apex of the heart, resulting in a harsh, typically loud heart murmur that occurs during systole. When the posterior leaflet is more severely affected, as is commonly the case in humans with mitral valve degeneration, then the murmur may be much softer as the jet of mitral regurgitation is directed towards the interatrial septum and away from the body wall.

If the amount of mitral regurgitation is small, then it is not hemodynamically significant, meaning it does not cause any significant changes to the heart structure or to the circulation. According to guidelines from the American College of Veterinary Internal Medicine (ACVIM), dogs with this stage of disease are classified as having stage B1 degenerative mitral valve disease. (Click here to learn more about the stages of heart disease.) If the disease progresses and the degree of mitral regurgitation due to valvular degeneration is severe enough, then the amount of blood leaking back into the left atrium places a volume overload in this chamber and subsequently the left ventricle. These chambers may then begin to remodel and enlarge as a result of the volume overload placed upon them in an effort to compensate. These changes in atrial and/or ventricular size may be detected by thoracic radiographs (chest x-rays) or echocardiogram (cardiac ultrasound). Dogs with this stage of the disease are classified as having stage B2 degenerative valve disease. If the disease progresses further, then left atrial pressures will rise, leading to subsequent elevation in the pulmonary venous and pulmonary capillary pressures within the lungs, at which point pulmonary edema (fluid within the lung tissue) will develop. This is known as left-sided congestive heart failure and requires medical and/or surgical therapy. Dogs with left-sided congestive heart failure that respond to standard medical therapy are classified as having stage C degenerative valve disease. A small number of dogs may become unresponsive (refractory) to standard medical therapy and are classified as having stage D degenerative valve disease.

It is important to note that although a large number of the canine population may develop degenerative valve disease over their lifetime, the majority of patients with the disease will not progress to developing congestive heart failure due to the slowly progressive nature of the disease itself, though in some dogs progression of the disease can be quite rapid. As already mentioned, other valves of the heart besides the mitral valve may be affected by degenerative valve disease. The tricuspid valve is the second most common valve affected by degenerative valve disease in dogs, and most dogs with mitral valve degeneration will have some degree of tricuspid degeneration. Only a small numbers of dogs will have evidence of aortic or pulmonic valve degeneration. Dogs with significant tricuspid valve degeneration and regurgitation may have changes to the right atrium and right ventricle similar to those seen on the left side of the heart with mitral valve degeneration. If the tricuspid regurgitation is severe enough, then right-sided congestive heart failure may develop. This results in a large volume of fluid accumulating in the body cavities and is most obvious in the abdomen (ascites).

One potential complication of chronic, long-standing, degenerative mitral valve disease is the development of pulmonary hypertension (high blood pressure within the arteries of the lungs). Pulmonary hypertension due to degenerative valve disease typically only occurs in dogs with more advanced stages of the disease (stages B2, C and D). It occurs as a result of increased left atrial pressures due to significant mitral regurgitation. Progressive “backing-up” of blood within the pulmonary circulation (veins, then capillaries, then arteries) occurs. The pulmonary arteries may then undergo a process called reactive vasoconstriction whereby the muscles in the walls of the pulmonary arteries contract and disproportionately increase the pressure with them. If identified early enough and if the dog’s left-sided heart disease is appropriately managed, then pulmonary hypertension due to degenerative mitral valve disease can be reversed. However, if the pulmonary hypertension is chronic and sustained over a long period of time, the changes may be permanent. Dogs with pulmonary hypertension may experience increased respiratory rate and/or effort or even respiratory distress without evidence of pulmonary edema. They may also experience weakness, lethargy and collapse or fainting episodes. If the pulmonary hypertension is severe enough then right-sided heart failure may develop.

Another, very rare, complication of degenerative mitral valve disease is acute rupture of major chordae tendineae. Though most cases of the disease may have ruptures to small chordae that contribute to mitral regurgitation, some dogs may develop acute rupture to larger, more substantial chordae tendineae. If this occurs, then the affected valve leaflet is essentially untethered, freely swings back and forth between the left ventricle and left atrium, and is unable to form any effective seal to prevent blood flowing back into the left atrium during cardiac contraction. This results in a massive and sudden increase in left atrial volume and subsequently left atrial pressure since the atrium has not had time to slowly enlarge and accommodate for the increased volume. The end-result is rapid and severe fulminant heart failure, sometimes so severe that pulmonary edema may develop and be seen coming from the nostrils as a pink-tinged froth. Unfortunately, acute chordal rupture is often so severe that many patients may die before veterinary assessment and treatment can be performed. However, it is at least a very rare, but still unpredictable, complication of the disease.

 

Clinical Signs

it is very important to note that canine degenerative valve disease is typically a slowly progressive disease, and so some dogs may live with heart disease for years before any signs of heart disease even develop and for the majority of dogs will never appear. Often the only sign of heart disease may be a heart murmur that your veterinarian can identify upon cardiac auscultation (listening to the heart sounds with a stethoscope). For this reason, routine annual visits (or every 6 months for geriatric dogs 8 years or older) to your vet are recommended as they may identify subtle changes long before overt signs due to degenerative valve disease may develop.

Signs your dog may have degenerative mitral valve disease and/or left-sided congestive heart failure include increased respiratory rate (called tachypnea) and/or effort (called dyspnea) when at rest, collapse or fainting episodes, weakness and lethargy, reduced exercise tolerance, cough, and blue discoloration of the gums or tongue (called cyanosis). Signs that may indicate degenerative tricuspid valve disease and right-sided heart failure include increased respiratory rate and/or effort, reduced exercise tolerance, weakness or collapse, abdominal swelling, swelling of the limbs or head, and distension or pulsation of the jugular veins in the neck. These signs may also be seen with pulmonary hypertension since it may worsen tricuspid regurgitation and lead to right-sided congestive heart failure in its own right. Coughing, usually persistent over a prolonged period, is also another sign that may be present in dogs with pulmonary hypertension. If you notice any of the above signs in your dog, then you should see your veterinarian, who can examine your dog and perform further diagnostics as necessary to confirm or rule out the presence of heart disease.

The most sensitive indicator of left-sided congestive heart failure in dogs with degenerative mitral valve disease is an elevated respiratory rate when at rest. For this reason, your veterinarian or veterinary cardiologist may recommend to count your dog’s resting respiratory rate at home if your dog has been diagnosed with stage B2 or stage C degenerative valve disease. This a very useful test to determine if your dog has impending pulmonary edema and needs to be re-evaluated by your veterinarian or veterinary cardiologist, and it should not be dismissed as a frivolous waste of time as it can be performed in as little as 15 seconds. The resting respiratory rate is best observed when your dog is in a nice, deep sleep (but not dreaming as their respiratory rate may be higher while they are dreaming of chasing rabbits or squirrels). To count the resting respiratory rate, simply watch your pet’s chest and count the number of breaths over 1 minute (or alternatively count the number of breaths over 15 seconds and then multiply by 4). Each rise and fall of the chest wall counts as 1 breath. In healthy dogs, the normal resting respiratory rate is less than 35 breaths per minute. Rates that are consistently higher than this may indicate the presence of pulmonary edema due to left-sided congestive heart failure, and a visit to your veterinarian is recommended. Coughing is a relatively insensitive indicator of the presence of heart failure and can also be caused by a wide range of diseases affected the airways or lungs. Nevertheless, presence of a cough, particularly one that continues to worsen, should warrant investigation by your veterinarian.

Syncope is a term for fainting due to a transiently decrease in bloodflow to the brain and may be seen in dogs with advanced degenerative valve disease. The exact cause may differ between different dogs. In the majority of dogs with syncope due to degenerative valve disease it is a vagally-mediated response – basically a sudden increase in systemic blood pressure (as can occur with excitement, activity or stress) can lead to slowing of the heart as well as increasing the amount of blood leaking back through the mitral valve, thus reducing the cardiac output to the rest of the body. This a transient response, however, and is rarely fatal. There is no specific treatment for vagally-mediated syncope. However, many dogs can be effectively managed by limiting their exposure to known triggers such as excessive activity (i.e. running up the stairs) or excessive excitement (such as for those dogs that go wild at the sight/sound of the pesky postman). Other potential causes of syncope in dogs with degenerative valve disease include arrhythmias, which are irregular heart rhythms and may be due to structural changes within the heart muscle (such as scar tissue) secondary to the disease, and pulmonary hypertension as described earlier (see above). Both of these causes, in particular arrhythmias, may potentially be fatal. There are also several non-cardiac causes of syncope in dogs, and additionally, seizure activity in dogs may also closely resemble syncope in some cases. If your dog experiences episodes of collapse/syncope, it is important to have them examined by your veterinarian to identify the underlying cause and start any appropriate treatments if necessary.

 

Physical Examination

Auscultation is one of the most important parts of the physical examination, which is when your veterinarian listens to your dog’s heart and lungs using a stethoscope. During auscultation, your vet will listen to determine if your dog has normal heart sounds, normal lung sounds and a normal rhythm. They will also listen for additional heart sounds, specifically murmurs and mid-systolic clicks. Heart murmurs are “swooshing” sounds created by turbulent blood flow and are most commonly associated with diseases that affect the heart valves, such as degenerative valve disease. Murmur intensity is typically graded on a scale from 1-6 with grade 1/6 being the lowest intensity and softest murmur and grade 6/6 being the loudest murmur; however, some vets use a scale of 1-5. In most small breed dogs if there is no heart murmur present, then there is no significant degenerative valve disease present. Typically, murmurs due to degenerative valve disease in dogs are harsh-sounding murmurs that occur during systole (period of cardiac contraction) and are best heard over the left apex of the heart on the left side of the chest since this is the region where the mitral valve can be best heard. In dogs with very loud murmurs (grade 5/6 or grade 6/6) there will be a palpable precordial thrill: this is a buzzing or vibrating sensation that can be felt on the chest wall at the location of maximum murmur intensity and is a result of a severe, turbulent jet of regurgitation directed towards the chest wall.

In dogs with degenerative valve disease, severity of murmur intensity is typically directly related to the severity of the disease. However, this may not always be the case, particularly in larger breed dogs and dogs in which the regurgitant jet is directed away from the body wall (such as when the posterior mitral leaflet is the main leaflet affected).

Mid-systolic clicks are clicking sounds that may be heard between the “lub” and the “dub” of the heartbeat. They are most commonly associated with prolapse of the mitral valve during the early stages of degenerative valve disease before a murmur develops. As the disease progresses, the click usually becomes inaudible due to the development of the heart murmur caused by leakage of blood through the degenerative valve.

In addition to auscultation, your vet will also perform a complete physical examination. Check out for our blog post on physical examination to help identify other signs of cardiac disease, as discussed previously, or any other disease that may be causing those clinical signs. Based on the results of their examination, your veterinarian may suggest further diagnostic tests such as thoracic radiographs (chest x-rays), echocardiogram (cardiac ultrasound), bloodwork or urine testing in order to reach a definite diagnosis or to stage your pet’s heart disease, if present. Learn about these other diagnostic tests below…

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Why is a thorough physical examination by your veterinarian so imperative to your pet’s overall health? Find out all that your vet can learn about your pet through a physical exam in our article.

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Diagnostics

Radiographs

If your veterinarian suspects degenerative mitral valve disease, he or she will likely recommend thoracic radiographs (chest x-rays) to determine what stage of the disease your dog is in and if there is evidence of left-sided congestive heart failure that requires treatment. Dogs with stage B1 disease will have no structural changes, so their heart and vasculature will appear normal on a chest x-ray. Once dogs advance to stage B2 disease, there should be evidence of left atrial and/or left ventricular enlargement +/- enlargement of the pulmonary veins on chest x-rays. When left-sided congestive heart failure develops (stages C and D), all of the changes seen in stage B2 should be evident. Additionally, pulmonary edema will become evident on chest x-rays, primarily in one of two patterns: an interstitial pattern, or an alveolar pattern (sometimes a mix of both may be present). These patterns typically appear in the right caudal perihilar region of the chest on thoracic radiographs in the initial stages of left-sided congestive heart failure. However, in more severe or more long-standing cases, then remaining portions of the caudal and dorsal lung fields can be affected.  The pulmonary veins also become enlarged on x-rays when left sided congestive heart failure is present. Thoracic radiographs are also a very important way to monitor the response to treatment of left-sided congestive heart failure and are recommended to be repeated typically 1-2 weeks after starting treatment, (which will be discussed later) in order to ensure the pulmonary edema has resolved and that your dog is no longer in congestive failure.

Thoracic radiographs can also identify signs of right-sided heart failure, in particular pleural effusion which will be seen as a rim of fluid opacity surrounding the lungs and, if severe enough, will make the lungs and heart very difficult to see. Your veterinarian may also recommend performing abdominal radiographs instead of or in addition to thoracic radiographs to look for free abdominal fluid (ascites) if he or she suspects right-sided congestive heart failure. Thoracic radiographs also allow your veterinarian to assess your pet’s lungs and airways to look for other potential causes for respiratory signs your pet may be experiencing.

Your veterinarian may recommend repeating thoracic radiographs at various time-points to monitor for progression of your pet’s heart disease. The main limitations of thoracic radiographs in patients with heart disease are that they do not give any information on the function of the heart muscle and are unable to give definitive information on the internal structure of the heart, i.e. the heart valves. Radiographs are also less sensitive than echocardiography in detecting subtle changes in heart chamber sizes. Your veterinarian may instead or in addition recommend an echocardiogram (cardiac ultrasound) in order to gain further information to reach a definite diagnosis, determine prognosis or guide what, if any, treatments are necessary.

 

Echocardiography (Echo)

Echocardiography is a safe, painless, non-invasive diagnostic test, in which an ultrasound probe is used to send out echo signals that then bounce off the structures within the chest and send a signal back to the probe, which are then translated into an image displayed on a screen. This allows the heart, including its internal structures, to be viewed in real-time so that the contraction of the heart muscle and the function of the valves can be closely assessed. Cardiac chamber dimensions can be accurately measured with echocardiography. Computerized mapping of the ultrasound signals allows turbulent bloodflow to be displayed on the image of the heart and aid in diagnosis of murmurs.

Depending on the stage of your dog’s degenerative valve disease, your dog may or may not have evidence of atrial and/or ventricular enlargement. Mitral or tricuspid valves affected by the disease will appear thickened and irregular in appearance and may also have evidence of prolapse, where they bulge back into their respective atrium. There will be evidence of mitral or tricuspid valve regurgitation which can be subjectively assessed in terms of severity based on the size and appearance of the jet on echocardiography.  Some dogs may have evidence of partial or complete flail (swinging of the leaflet tip or whole leaflet respectively) of a valve leaflet if there has been previous rupture of minor or major chordae tendineae, respectively. In dogs with advanced degenerative valve disease there may be evidence of systolic dysfunction: this is when the ventricular muscle becomes weaker as a result of the volume overload secondary to valvular regurgitation and the end result is reduced contractility of the heart muscle, which can reduce cardiac output further. If tricuspid valve regurgitation or pulmonic valve insufficiency are present, then pulmonary arterial pressures may be estimated by echocardiography and so echocardiography can be used to non-invasively identify the presence of pulmonary hypertension in dogs with degenerative valve disease.

Echocardiography is a somewhat advanced imaging technique that requires advanced training and somewhat specialized equipment. In the majority of cases, your veterinarian will refer you to a veterinary cardiologist to have this procedure performed however, some veterinarians will have the training and equipment to provide this service at their own facility. Echocardiography is very important for identifying which dogs with advanced stage B2 degenerative valve disease meet the criteria, at which, therapy with pimobendan is known to delay disease progression and so is used to determine the optimal time for starting this medication. Your veterinary cardiologist will also be able to recommend additional or alternative medications if your pet has heart failure which is unable to be well controlled with standard treatments. Your veterinarian or veterinary cardiologist may recommend follow-up echocardiograms at various time-points to monitor for progression of your dog’s degenerative valve disease or pulmonary hypertension if present. The main limitation with echocardiography is that is does not give any reliable information on the present of pulmonary edema and so cannot replace radiographs for the definitive diagnosis of left-sided congestive heart failure.

 

Electrocardiography (ECG aka EKG)

If your veterinarian identifies an arrhythmia (irregular heart rhythm) upon examination they may suggest an ECG to determine the exact type of arrhythmia and determine if treatment with anti-arrhythmic drugs is necessary. Intermittent atrial premature complexes (APCs) are probably one of the most common causes for an irregular heart rhythm in dogs with degenerative valve disease but in the majority of cases do not require treatment however some dogs may develop atrial tachycardia that may need to be treated. Some dogs with very severe atrial enlargement may develop atrial flutter or fibrillation that will required treatment with anti-arrhythmic drugs such as diltiazem or digoxin.

 

Blood Pressure Measurement

As part of a complete cardiac investigation, your veterinarian or veterinary cardiologist may recommend blood pressure measurement. In dogs with degenerative mitral valve disease, high blood pressure (hypertension) can increase the severity of mitral regurgitation and result in quicker disease progression and worsen the severity of left-sided congestive heart failure. Treatment with anti-hypertensive drugs such as amlodipine may help in hypertensive dogs with degenerative valve disease.

 

Bloodwork for dogs with degenerative valve disease

If your veterinarian or veterinary cardiologist suspects or has diagnosed degenerative disease may recommend one or more of the following blood tests depending on the stage of the disease:

• Serum biochemistry profile – this profile assesses the main biochemical markers of organ dysfunction within the body. Of particular interest to your veterinarian will be: markers of renal function, i.e. blood urea nitrogen (BUN) and serum creatinine (Crea) which indicate kidney function and are particularly important if your pet is receiving diuretic therapy for their heart disease or if your veterinarian is planning on prescribing diuretic therapy; markers of liver damage/dysfunction, i.e. serum alanine transaminase (ALT) and alkaline phosphatase (ALKP), which indicate damage to the liver cells or the cells of the bile ducts respectively and may be elevated secondary to liver congestion as a result of right-sided heart disease; serum electrolytes, particularly sodium (Na⁺), potassium (K⁺) and chloride (Cl^–) as derangements in levels of these electrolytes may frequently occur with diuretic therapy as well as result in certain arrhythmias.
  • Renal biochemical profile – this is an abbreviated version of the serum biochemical profile which concentrates markers of kidney function i.e. BUN, Crea, Na⁺, K⁺ and Cl^–. It may also include a packed cell volume (PCV), which is typically performed as part of a complete blood count (CBC). This profile is more cost effective than a full serum biochemistry profile in patients in which long-term routine monitoring of renal function is necessary, i.e. patients on long-term diuretic therapy.
• Heartworm antigen test –This test is highly recommended if your pet displays signs of right-sided heart disease and lives or has a history of travel to/from heartworm endemic areas. Heartworm disease, if present can cause pulmonary hypertension and cause or worsen the severity of tricuspid valve regurgitation in dogs with degenerative valve disease.
• N-terminal pro-brain natriuretic peptide (NT-proBNP) assay – NT-proBNP is a small protein released in response to enlargement and stretching of the atria in the heart. High levels may indicate atrial enlargement in dogs with degenerative valve disease. However, NT-proBNP levels need to be interpreted with caution as not all animals with atrial enlargement will have increased NT-proBNP levels and, conversely, not all dogs with elevated NT-proBNP will have atrial enlargement, which may be seen in dogs with renal disease resulting reduced elimination of the NT-proBNP from the body. This test has limited usefulness as it does not provide any additional information if chest x-rays and/or echocardiography have already shown evidence of atrial enlargement. It may be helpful to rule in heart disease in settings where chest x-rays or echocardiography are not available.

 

Treatment

Treatment of degenerative valve disease is very variable depending in the stage of the disease. For this reason, it is important that your dog’s heart disease is appropriately investigated and staged by your veterinarian or veterinary cardiologist.

 

Medical Therapy

• Stage A, stage B1 and early stage B2 degenerative valve disease:
  • There are no medical therapies proven to delay progression of degenerative valve disease or have an effect on survival in dogs in stage A, stage B1 or early stage B2 disease and so medical treatment in these dogs is not required. Dogs with stage B1 and early stage B2 disease should be routinely monitored, ideally with echocardiography, to identify progression to advanced stage B2 disease with significant atrial and ventricular enlargement. As mentioned, degenerative mitral valve disease is typically slowly progressive and so many dogs will not progress to a stage where medical therapy is required.

• Advanced stage B2 degenerative valve disease:
  • Relatively recently, pimobendan has been shown to delay the onset of left-sided congestive heart failure in dogs with advanced stage B2 degenerative mitral valve disease. In the study that demonstrated this effect, dogs were only classified as having advanced stage B2 degenerative mitral valve disease if they met all three of the following criteria:
    1. vertebral heart score greater than 10.5 based on a lateral thoracic radiograph;
    2. left atrium:aortic root ratio greater than 1.6 determined from echocardiography;
    3. end-diastolic left ventricular dimension indexed to bodyweight of greater than 1.7 determined from echocardiography.
  • Since there is currently no evidence that pimobendan has any additional effect in delaying the onset of left-sided congestive heart failure in dogs with less advanced stages of degenerative mitral valve disease (including early stage B2 disease), and the disease itself is typically slowly progressive in most cases, pimobendan therapy prior to the development of heart failure should typically be reserved for dogs that meet all three of the criteria listed above. No other medical therapies have been shown to have a clear beneficial effect in this stage of the disease.

• Stage C and stage D degenerative valve disease:
  • Since congestive heart failure is the hallmark of stage C and stage D degenerative valve disease, the aims of medical therapy are to reduce the volume imposed on the left or right atrium due to valvular regurgitation. At a minimum, standard medical therapy for left- or right-sided congestive heart failure consists of life-long treatment with the following:
    1. A diuretic – furosemide (ex. Lasix®, Salix®) is the most common diuretic used to treat congestive heart failure in dogs. Other diuretics used to treat congestive heart failure in dogs include torsemide and hydrochlorthiazide. Diuretics will cause your pet to urinate more and subsequently drink more so be prepared for accidental urination around the house. Once your pet has been prescribed diuretics, they require free access to water at all times to avoid injury to the kidneys. Since diuretics cause the kidneys to work harder, routine monitoring of kidney values on bloodwork is recommended to help adjust to the lowest effective dose and ensure that unnecessary side effects on the kidneys are avoided as much as possible.
    2. Pimobendan (ex. Vetmedin®) – this medication is a positive inotrope and vasodilator that has been shown to significantly increase survival time in dogs with left-sided congestive heart failure due to degenerative mitral valve disease when given in addition to diuretic therapy. Pimobendan is not stable in water-based solutions, and so liquid compounding of this medication is not recommended. Generally, pimobendan is well-tolerated with few side effects. Potential side effects typically include inappetance or gastrointestinal upset, and so pimobendan is usually recommended to be given on an empty stomach usually one hour before food.
    3. An angiotensin converting enzyme inhibitor (ACEI) – the most commonly used ACEIs in veterinary medicine are enalapril and benazepril. These drugs blunt the renin-angiotensin-aldosterone system (RAAS), which is a neurohormonal pathway that promotes fluid retention and is excessively activated in heart failure and in the presence of diuretic drugs. They are typically started once the patient has been stabilized with diuretics and pimobendan and only once the patient’s appetite has returned to normal. Potential side effects include inappetance, gastrointestinal upset and weakness.

In addition to standard medical therapies listed above, your veterinarian may also prescribe one or more of the following adjunctive therapies depending on the other clinical findings such as the presence of arrhythmias, the presence of pulmonary hypertension or the development of low serum potassium (hypokalemia) as a result of diuretic therapy.

• Spironolactone – this is a potassium-sparing diuretic with very weak diuretic effects and is not strong enough to control congestive heart failure by itself. It is, however, often added to standard medical therapy for congestive heart failure if there is evidence of hypokalemia (low serum potassium) on bloodwork, which can be a result of diuretic therapy. It primarily works by blocking a hormone called aldosterone and so, like ACEIs, may blunt the body’s mechanisms to retain water in the face of heart failure and diuretic use. Studies in rodents also suggest it may reduce the amount of secondary remodeling of the heart due to certain cardiac diseases.
• Sildenafil – this medication is related to pimobendan and is probably better known by one of its more common brand names, Viagra®. This medication is used to specifically dilate the arteries within the lungs and so is used for the treatment of pulmonary hypertension (high blood pressure in the lungs). It is typically given once or twice daily, and potential side-effects include weakness and collapse.
• Amlodipine – this is a calcium channel blocking drug used to treat systemic hypertension (high blood pressure) in cats typically, but it may also be prescribed for dogs (though its efficacy in dogs is not well known). It is usually well tolerated however. Potential side-effects include weakness, lethargy and inappetance.
• Antiarrhythmic Drugs – there are many different types of anti-arrhythmic drugs used to treat arrhythmias in dogs. They can be broadly broken down into 4 main classes based on their mechanism of action: sodium channel blockers; beta blockers; potassium channel blockers; and calcium channel blockers. Other miscellaneous antiarrhythmic drugs exist that do not lend themselves to this type of classification. Diltiazem and digoxin are two of the more commonly prescribed antiarrhythmic drugs in dogs with degenerative valve disease and are typically used to treat atrial fibrillation. More information on antiarrhythmic medications can be found here.

In recent years, angiotensin receptor blockers (ARBs) have been shown to significantly benefit human patients with congestive heart failure. There is limited study into their effect in dogs with degenerative valve disease though it is possible their use may increase in the coming years. They are used instead of ACEIs and also work to blunt the effects of the RAAS to retain fluid, stimulated by heart failure and diuretic therapy, by blocking a different part of the RAAS pathway than ACEIs.

 

Surgical therapy

Unlike in humans, cardiac surgery performed under cardiopulmonary bypass is not readily available for the majority of dogs with degenerative valve disease. This is primarily a result of the significantly increased cost, equipment and expertise required for these types of procedures. In humans, degenerative mitral valve disease is essentially a surgical disease with surgery being the treatment of choice. However, due to the limitations in the veterinary field as mentioned above, medical management of congestive heart failure is still the mainstay of treating the condition in dogs. However, there are a very small number of facilities worldwide in which this procedure is successfully performed in dogs. With successful surgical treatment, the progression of the disease can essentially be halted and congestive heart failure can be reversed, thus eliminating the need for medical therapy. In addition, there are several minimally-invasive “beating heart” devices and techniques being developed for valvular repair in humans that may find a role in mitral valve repair in dogs in the future. Consult with your veterinary cardiologist if you wish to find out more information about mitral valve repair surgery for your dog.

 

Abdominocentesis/Thoracocentesis

In some dogs with severe right-sided heart failure due to tricuspid valve degeneration and/or pulmonary hypertension, drainage of free abdominal fluid (ascites) or free fluid around the lungs (pleural effusion) may be necessary to provide immediate relief of pressure in the abdomen and reduce compression of the lungs, respectively, before standard medical therapies can take effect. Depending on the cavity being drained, this is called abdominocentesis or thoracocentesis and is performed using a needle attached to a syringe via tubing and may or may not require sedation depending on your dog’s temperament and stoicism. These procedures can safely be performed with or without ultrasound guidance.

 

Diet

Similar to human patients, ideal diets for animals with degenerative valve disease should be low in sodium as sodium promotes water retention. There are a small number of prescription cardiac diets available as well as recipes available for homemade low-sodium diets for your dog. Unfortunately, restricting the sodium content significant reduces palatability of these diets, and so dogs will often refuse to eat them. One of the biggest risks with inappetance in dogs with degenerative valve disease is the loss of muscle mass over time, which includes cardiac muscle mass and thus increases the workload on an already failing heart. For this reason, I suggest to stick with a healthy, balanced diet that your pet enjoys and eats readily and to avoid treats high in sodium, which unfortunately is most treats. Pieces of boiled or grilled chicken breast with no added salt is often a good option for treats in dogs or cats with heart disease. Omega-3 and omega-6 fatty acids may also have a positive role in cardiac health and so may be recommended by your veterinarian or veterinary cardiologist. Click here for more nutrition information for pets with heart disease, courtesy of Tufts Cummings School of Veterinary Medicine.

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Learn about the potential health benefits of omega fatty acids for dogs and cats! Click here for our article.

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Exercise

Strict exercise restriction is typically not required for most dogs with degenerative valve disease. Dogs with stage A, stage B1 and early stage B2 disease can be allowed to exercise as normal. Unrestrictive, high-intensity exercise should be avoided in dogs with advanced stage B2 and stage C disease, but they should otherwise be allowed to perform as much controlled exercise as they choose. Dogs are typically quite good at self-regulating their exercise in the presence of degenerative valve disease and usually will only do as much as they feel up to. If you notice your canine comrade gets a little more out of breath or seems more tired than usual after his or her usual walking distance, then reduce the distance down until they are able to perform the activity without any adverse effects.

 

Follow-up

The type and frequency of follow-up examinations by your veterinarian or veterinary cardiologist will be dependent on the stage of degenerative disease your dog has and what therapies they are receiving. Typically, dogs with soft, left apical, systolic murmurs and no evidence of cardiac enlargement on x-rays only require re-evaluation (including chest x-rays or echocardiography) every 12 months or so until there is evidence of cardiac enlargement. Re-evaluation including chest x-rays or echocardiography +/- blood pressure measurement should be performed sooner if there is a change in murmur character or intensity or if clinical signs of cardiac disease, as discussed earlier, develop (see above). Dogs with left apical, systolic murmurs and newly identified evidence of cardiac enlargement (i.e. stage B2 dogs) should have echocardiographic re-evaluations performed every 6-12 months to monitor echocardiographic dimensions and determine when pimobendan therapy should be started (as discussed previously). Once dogs have been diagnosed with advanced stage B2 disease and are receiving pimobendan therapy, then re-evaluation with chest x-rays every 6-12 months is recommended; counting of the resting respiratory rate once a night at home is also recommended. Re-evaluation with your veterinarian should be performed sooner if the resting respiratory rate is consistently increased above 35 breaths per minute or if other clinical signs associated with heart disease develop. Dogs that have been diagnosed with congestive heart failure and that are receiving standard medical therapy as described above should be re-evaluated in approximately 7-10 days to repeat chest x-rays and a renal blood profile to determine that appropriate control of congestive heart failure has been achieved and if a reduction in diuretic dose is required. A renal blood profile (scroll up for details) should be repeated every 3 months in dogs receiving long-term diuretic and ACEI therapy for congestive heart failure.

 

Prognosis

Overall, the prognosis for canine degenerative valve disease is very variable and is heavily dependent on the stage of the disease your dog has, what additional valves are affected and if there are any concurrent complications such as pulmonary hypertension or arrhythmias. Appropriate diagnosis and staging of your dog’s cardiac disease are, therefore, essential. Consult with your veterinarian or veterinary cardiologist if your dog displays any signs associated with cardiac disease as discussed above or if signs reappear after successful medical or surgical treatment.

The majority of dogs with degenerative valve disease will not develop clinical signs or congestive heart failure. Degenerative valve disease is typically a very slowly progressive disease and may take years for clinical signs of disease to develop, if they ever do so. Of those dogs that do go on to develop left-sided congestive heart failure due to degenerative mitral valve disease with no additional complications, typical survival times of 9-18 months years can be expected. However, these times may be shorter or longer depending on various factors. Though rupture of major of chordae tendineae is very rare in dogs with degenerative mitral valve disease, it is very acute and unexpected when it does occur and is usually fatal. Arrhythmias secondary to degenerative valve disease are also very uncommon but may cause sudden unexpected death in dogs with the disease.

One of the most important factors in long-term survival in dogs with left- or right-sided congestive heart failure is the balance between maintaining adequate heart function and maintaining adequate kidney function. Many dogs will develop some renal changes as a result of diuretic and ACEI therapy for congestive heart failure but typically the changes are mild and dogs are usually able to compensate well without showing any significant clinical signs of kidney dysfunction. Unfortunately, some dogs experience congestive heart failure and renal failure together, which is a very difficult situation to treat as a reduction in the body’s fluid levels is required to treat heart failure whereas administration of excess fluid is required to treat renal failure to help the kidneys perform their function to remove toxins from the body. Ultimately, one of these conditions requires preferential treatment over the other, and very often adequate kidney function is sacrificed for adequate heart function since dogs will die much quicker from congestive heart failure than they will from chronic kidney failure and, in many cases, will cope rather well with their kidney disease. As previously discussed, routine monitoring of your dog’s kidney values by your veterinarian is of huge importance if your dog is receiving diuretic therapy for heart failure in order to adjust your pet’s diuretic dose to the lowest effective dose to avoid unnecessary kidney injury.

Congestive heart failure, even with successful management, is usually a terminal condition in most cases, except in dogs that have undergone successful surgical valve repair. If you own a dog that has been diagnosed with congestive heart failure due to degenerative valve disease, you will likely one day be in that unenviable position of having to determine when your dog’s quality of life is reduced and allow your four-legged family member to have a dignified and peaceful passing via euthanasia. However, by working closely with your veterinarian and your veterinary cardiologist, you can give your canine companion the best quality of life for as long as possible. That being said, the vast majority of dogs with degenerative valve disease will not progress to develop congestive heart failure as a result of their disease and will go on to lead normal and happy lives.

 

– Michael Aherne, MVB (Hons 1), GradDipVetStud, MS, MANZCVS (Small Animal Surgery), DACVIM (Cardiology)

 

Meet our author: Michael Aherne, MVB (Hons 1), GradDipVetStud, MS, MANZCVS (Small Animal Surgery), DACVIM (Cardiology) – Dr. Michael Aherne is a boarded veterinary cardiologist with the American College of Veterinary Internal Medicine (ACVIM). Earning his Bachelor of Veterinary Medicine (MVB) at University College Dublin (UCD) in Dublin, Ireland, Dr. Aherne has garnered additional advanced veterinary training in Australia as well as in the United States. He currently holds a university position as clinical assistant professor in cardiology at the University of Florida (USA).

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Read Dr. Aherne’s previous article on The Meowing Vet‘s website on Congestive Heart Failure (CHF) in dogs and cats to stay informed about the most common cardiac conditions afflicting pets and what you as a pet owner need to know!

You can also learn more about heart disease in pets with these articles, courtesy of Tufts Cummings School of Veterinary Medicine.

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