Valvular heart disease (VHD) is a condition caused by the breakdown and thickening of the valves of the heart. In order to understand the impact of this disease, we need to look at the anatomy of your pooch’s heart.
Your dog’s heart, like yours, is a four-chambered pump made of muscle. The valves of the heart work to keep blood flowing in the correct direction. Normally, blood moves first into the atrium, the pump primer. The atrium contracts, pushing blood into the ventricle, which is the pump. Normal pump function requires that blood move always in this direction. However, with VHD, degenerative changes in the valve between the atrium and the ventricle cause it to become thick and distorted. As a result, the edges don’t make a tight seal when the valve shuts and small amounts of blood leak from the ventricle into the atrium with each heartbeat. To compensate for this leaky valve, the heart has to pump more blood with each beat, causing the heart to enlarge over time.This extra work load causes the heart to become ineffective and unable to keep up with the body’s demand for blood flow. This inability to supply the body with the blood it needs is known as heart failure.
VHD is a very common, progressive disease often found in older dogs; it affects breeds such as:
- Lhasa apsos
- Toy poodles
- Yorkshire terriers
- Cocker spaniels
- Cavalier King Charles spaniels
- Small mixed-breeds
In the early stages of heart disease, your dog’s body is able to make adjustments that allow her to cope with the disease. During this stage, your dog may show no visible signs of being sick. As time goes on and the valvular heart disease progresses, her body will no longer able to make these adjustments. As a result, you may notice any of the following symptoms:
- Difficulty breathing
- Exercise intolerance
- Pale gums
- Loss of appetite
Your veterinarian will perform a very thorough physical examination, which includes listening to your dog’s heart.
Your veterinarian may also recommend the following to help diagnose your dog’s condition:
- A radiograph, commonly known as an x-ray
- A blood test for a cardiac biomarker called NTproBNP
- A CBC and chemistry profile to assess your dog's overall health
- A blood pressure test
- An ECG (electrocardiograph) to record your dog’s heart’s electrical action
- An echocardiogram
If your dog is diagnosed with valvular heart disease, your veterinarian may prescribe the following treatment:
- Nutritional modification, such as a low-sodium diet
- Diuretics, to help clear this excess fluid
- Regular but controlled daily exercise
- For advanced cases, drug therapy—these drugs that relax blood vessels and make it easier for the blood to circulate are often given once a patient develops the symptoms described above
Unfortunately, VHD is a progressive disease that can’t be prevented. Routine veterinary visits for your best friend can help identify heart conditions such as VHD in their earliest stages. To learn more about canine heart disease, visit the Your Dog's Heart website.
If you have any questions or concerns, you should always visit or call your veterinarian – they are your best resource to ensure the health and well-being of your pets.
Diagnosis of Cardiovascular Disease in Dogs
, DVM, DACVIM (Cardiology), Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University
A veterinarian often diagnoses cardiovascular disease by reviewing the medical history and signs, conducting a physical examination, and interpreting the results of specific tests or imaging procedures. The physical examination includes using a stethoscope to listen to the sounds made by the dog’s internal organs, especially the heart, lungs, and abdominal organs, and examining parts of the body by feeling with hands and fingers to distinguish between solid and fluid-filled swellings and to examine pulses. Imaging techniques include x-rays electrocardiography (recording electrical activity of the heart) and echocardiography (a type of ultrasonography). Most cardiovascular diseases can be highly suspected by physical examination and x-rays. X-rays are also used to monitor the progression of congestive heart failure. Electrocardiography is specific for diagnosis of arrhythmias. Echocardiography is excellent for confirming tentative diagnoses, for assessing the severity of leaky heart valves or narrowed vessels, for evaluating chamber sizes and heart muscle function, for diagnosing high blood pressure in the lungs, for identifying birth defects in the heart, for detecting heart tumors, or for detecting pericardial disease (problems with the membrane surrounding the heart). Occasionally, more specialized tests such as cardiac catheterization (using a thin flexible tube inserted and threaded through an artery into the heart) or nuclear studies (x‑ray tests that include injection of radioactive isotopes) are necessary. Heartworm disease is diagnosed best by performing a blood test to detect the presence of female heartworms.
Electrocardiograms can show cardiac arrhythmias and other abnormalities in dogs.
Common Types of Imaging Used to Diagnose Heart Disease
X-rays (also called radiographs) of the chest frequently help diagnose heart disease in pets. Finding generalized enlargement of the heart or enlargement of specific heart chambers makes the presence of heart disease more likely. The images may also provide clues as to the specific disease present. For example, fluid in the lungs is a common finding in congestive heart failure. Although chest x-rays are useful in evaluating patients with heart disease, they have certain limitations. The presence of fluid in the lungs does not definitively confirm a disease originating from the heart or exclude another origin, such as pulmonary (lung) disease. Also, assessment of overall heart size and the size of specific heart chambers is typically far less accurate than testing by echocardiography (ultrasonography).
Electrocardiography is the recording of the heart’s electrical activity from the body surface with the use of electrodes. It can be used to identify heart arrhythmias, such as bradycardia (slower than expected rhythm), tachycardia (faster than expected rhythm), or other abnormalities of rhythm (such as sinus arrhythmia or sinus arrest).
Electrocardiography can also detect conduction disturbances, or failures of the electrical signals that cause the heart to contract to pass through the heart tissue. These include first-, second-, and third-degree atrioventricular block.
Finally, electrocardiography can identify chamber enlargement, which is indicated by waveform abnormalities shown on the electrocardiogram recording. Different readings suggest enlargement of the different chambers. While the electrocardiogram may suggest chamber enlargement, chest x-rays and echocardiography (ultrasonography) are more effective.
Echocardiography is a type of ultrasonography used to evaluate the heart, the aorta, and the pulmonary artery. Echocardiography complements other diagnostic procedures by examining and displaying the working heart and moving images of its action. Heart chamber and wall dimensions can be determined the physical structure and motion of valves can be seen and pressure differences, blood flow volumes, and several measurements of heart function can be calculated. There are 3 main types of echocardiography: 2-dimensional, m-mode, and Doppler. Two-dimensional echocardiography provides a wedge-shaped, 2-dimensional video of the heart as it moves. M-mode echocardiography is produced by a 1-dimensional beam of ultrasound that penetrates the heart, providing an “ice-pick view.” Differences in tissue density that are detected by the beam are then plotted on a screen. This is typically used to measure chamber size, wall thickness, valve motion, and the size of the aorta and pulmonary artery. Doppler echocardiography detects changing frequencies of the ultrasonic beam as it contacts moving red blood cells to measure the speed of blood flow and thus identify turbulent or high-speed flow. This can locate heart murmurs.
Cardiac catheterization involves the placement of specialized catheters (thin, flexible tubes) into the heart, aorta, or pulmonary artery. Cardiac catheterization may be performed when other diagnostic tests are insufficient to identify specific heart abnormalities or are unable to identify the severity of a lesion. It may also be used for presurgical evaluation, treatment, and in clinical research. Diagnostic and presurgical cardiac catheterization, however, have largely been replaced by echocardiography (see above). Most of the time now, cardiac catheterization is done to surgically repair defects in the heart.
Many heart disorders are more common in certain breeds. For example, mitral regurgitation is more common in Cavalier King Charles Spaniels, dilated cardiomyopathy is common in middle-aged Doberman Pinschers, and arrhythmogenic right ventricular cardiomyopathy usually affects Boxers. Older Miniature Schnauzers may develop specific types of arrhythmias, and tetralogy of Fallot is more common in young Wirehaired Fox Terriers. Knowledge of these and other breed associations with heart disease can often help your veterinarian make a diagnosis.
Diagnosis of Degenerative Mitral Valve Disease in Dogs
Diagnosis of DMVD is one of the easiest clinical aspects of the disease. A presumptive diagnosis can be made on the basis of patient signalment and physical examination, wherein the hallmark finding is an adult small-breed dog with a left-sided systolic murmur. In these instances, it is reasonable to assume that the source of the murmur is MR and hence, DMVD is present. Once a diagnosis has been made, the next question is: what is the severity of DMVD?
Staging and management of canine mitral valve disease
Heart failure refers to a clinical syndrome of symptoms and signs caused by impairment of the heart so, if there are no clinical signs, then the dog does not have heart failure.
In 2009, the ACVIM produced a staging system for canine mitral valve disease, and these stages will now be reviewed in turn.1 It is important to consider, however, that heart disease is a continuous process and doesn’t always jump nicely from one stage to the other (see Figure 1).
- Stage A: these dogs do not have evidence of heart disease, but are at risk from a genetic point of view dogs that are predisposed to mitral valve disease are in stage A, for example any Cavalier King Charles Spaniel.
- Stage B1: this refers to dogs that have heart disease (characterised by a typical mitral regurgitation murmur) but do not have an enlarged heart on radiography/echocardiography or clinical signs of the disease.
- Stage B2: mitral valve disease patients should be considered at this stage when evidence of cardiac enlargement on echocardiography/radiography is present but still no clinical signs of the disease are apparent.
No treatment has yet been shown to delay the onset of heart failure in these patients but this is still being actively researched. The main focus at this stage is therefore monitoring to ensure that intervention is provided as soon as possible to avoid, for example, a sudden jump from being stable to requiring hospitalisation.
Monitoring of the resting or sleeping respiratory rate at home can be very useful. Most dogs have a respiratory rate at home that is