Heart disease is a serious problem that affects a large number of dogs.
The heart is a muscular organ consisting of four chambers, two of which are located on the left side of the heart, and two on the right side. Each side of the heart also has a set of valves. When heart disease is present, certain parts of the heart cease to function properly.
Heart problems in dogs can be very serious and life threatening and often present without our awareness or prior warning. They can vary from congenital or hereditary problems that they are born with, to problems of old age such as congestive heart failure in dogs or secondary to other conditions such as hyperthyroidism (overactive thyroid).
There are two common heart conditions –
- Valvular Insufficiency and Congestive Heart Failure
This page will discuss Cardiomyopathy.
What is Cardiomyopathy?
Cardiomyopathy is the name applied to an abnormality of heart muscle function. The heart’s pumping ability is reduced, resulting in signs such as;
- Inability to exercise
- Fluid collection in the lungs, abdomen and limbs
- Emboli (clots that arise in the heart and travel to the kidney, brain, or legs)
Although some patients with cardiomyopathy do not develop clinical signs, others experience rapid progression of their disease or sudden death.
What are the causes?
The causes of cardiomyopathy include;
- Genetic predisposition
- Toxic causes (drugs and chemical compounds)
- Specific dietary insufficiencies
- Unknown causes
While some cases are entirely reversible, others are not and are treated with various levels of success.
Are there different types of cardiomyopathies?
Yes, there are three major forms of cardiomyopathies which occur in the dog species.
1. Dilated cardiomyopathy
In dilated cardiomyopathy, the heart muscle is weak and flaccid (floppy). This condition is associated with a reduction in heart muscle function during contraction (systole) and a decrease in forward flow of blood.
Subsequent upper heart chamber (left atrial) enlargement is associated with backup of blood and then fluid into the lungs (pulmonary edema) and so a cough often occurs.
2. Hypertrophic cardiomyopathy
Hypertrophic cardiomyopathy is a thickening of the lower heart muscle chambers (ventricles). This results are inappropriate heart function, obstruction of blood flow from the heart into the circulation, and enlargement of the upper heart chambers (atria). This abnormality is called diastolic dysfunction, a condition in which the heart fails to relax fully, fill, and then empty.
The resulting backup of pressures into the lung is responsible for the clinical signs of respiratory distress, coughing, and systemic emboli (blood clots).
- Unclassified or restrictive cardiomyopathies
Unclassified or restrictive cardiomyopathies are unidentified disease conditions in which heart problems are associated with severely enlarged upper chambers and diminished pumping ability. The clinical signs resemble those of hypertrophic cardiomyopathy.
Although not thickened, the ventricular muscle is dysfunctional and the heart is unable to fill and then pump adequately.
What are the signs of cardiomyopathy?
Cardiomyopathies are seen in both dogs and cats. The form in dogs is usually dilated, whereas hypertrophic and unclassified forms are identified most often in cats.
The diagnosis of cardiomyopathy is based on:
- History of weakness
- Fluid collection around the lungs and in the abdominal cavity
- Weight loss
- Seizures associated with fainting may occur
- Emboli (clots) can result in blood vessel blockage, sudden lameness, and cold painful limbs.
What are the clinical signs?
Clinical signs usually develop suddenly, often without apparent prior illness. In addition to these signs, the diagnosis depends on abnormalities found at;
- Irregularities occur in the heart’s rhythm and rate
- Abnormal heart sounds (murmurs) are heard with the stethoscope
- X-rays of the chest show heart enlargement
- Evaluation of the blood may identify complicating organ problems
- The electrocardiogram can diagnose an irregular heart rhythm and substantiate heart enlargement
Ultrasound examination of the heart confirms the suspicion of cardiomyopathy. We see;
- Dilatation of the heart cavity
- Poor contractility of the heart muscle
- Left atrial enlargement (with dilated cardiomyopathy).
- Thickening of the heart muscle
- Obstruction of the flow of blood into the circulation
- Left atrial enlargement (identify hypertrophic cardiomyopathy).
- Normal muscle thickness with disturbed function and enlarged left atria (indicates restrictive cardiomyopathy).
These images show an enlarged heart, fluid accumulation on the lungs and the trachea is pushed upwards due to the large heart.
What treatment is needed?
Treatment varies with the type of cardiomyopathy.
- Indicative of a loss of contractile heart strength, requires medications to improve strength (Pimobendin)
- To remove excess fluid accumulation (diuretics)
- To counteract abnormal hormone levels that contribute to heart failure (angiotensin-converting enzyme inhibitors)
- A low-salt diet is important to reduce sodium levels and subsequent water retention
- Nutrients such as taurine and carnitine may be required to counteract specific deficiencies
- Manual removal of excess fluid accumulation is sometimes necessary
Treatment of hypertrophic and unclassified cardiomyopathies
- Drugs to allow the ventricular muscle to relax may be used. This improves heart filling and blood flow to the body. Beta-adrenergic blocking agents or calcium-channel blocking agents often are used for this purpose.
- Removal of excess fluids from the body (diuretics)
- Sometimes manual removal of fluid from the chest space is necessary to improve comfort.
- Low-salt diets to counteract salt and water retention are indicated but may be difficult to achieve with a finicky and ill dog.
- Aspirin may be used to reduce the likelihood of blood clot formation within the heart.
- Antiarrhythmic agents to control irregularities of the heart’s rate and rhythm are called upon at times,
- Nutritional supplements in known deficiencies.
What is the prognosis?
- The prognosis for survival with cardiomyopathies varies from poor to good. Once cardiomyopathy has been recognized, much of the damage to the heart muscle has already occurred.
- The result is congestive heart failure, the signs and symptoms of which may be signs and symptoms of which may be treated for a variable period of time (often 3 to 12 months, which is equivalent to 3 to 5 years in a human). Although the pet may enjoy a period of good health and comfort, the long-term prognosis continues to indicate that heart failure will recur. As a result, the pet will become less responsive to medical intervention. Surgery is not yet an option for any form of cardiomyopathy.
- Early diagnosis of hyperthyroidism can be a preventative for the development of hypertrophic cardiomyopathy in dogs.
If at any time you are concerned that your pet is showing signs of heart failure you should contact the practice immediately for advice.
During routine consultations, such as yearly vaccinations and physical examinations, the veterinarian will assess your pets heart health by:
- asking questions regarding exercise and sleeping patterns.
- listening to the rate and rhythm of the heart with a stethoscope
- feeling how strong the pulse is
- assessing the colour of the mucous membranes in the mouth
- asssessing how quickly blood will flow back into the tissue of the gum after pressure is placed on the gum with a finger (called capillary refill time).
- sometimes the vet or nurse may also take your pets blood pressure