UNDERSTANDING HEART FAILURE IN DOGS

Heart failure is not a specific disease or diagnosis. It is a syndrome in which severe dysfunction results in the cardiovascular system's failure to maintain adequate blood circulation. Here, we examine this ‘syndrome’ in depth, including how it is diagnosed and what treatment options are available.

WHAT IS HEART FAILURE?

Any heart with a reduced ability to contract is a ‘failing’ heart. Almost any dog with heart disease that leads to heart chamber enlargement or increased heart wall thickness has a ‘failing’ heart. Still, at least initially, the body compensates for these changes, meaning that the dog has no external sign of difficulty and is not classified as being in heart failure or congestive heart failure.

A dog is considered to be in heart failure or congestive heart failure when he exhibits signs and symptoms related to a complex interaction between a failing heart and the blood vessels.

In non-congestive heart failure, the blood flow is too low volume or pressure to supply the organs with enough oxygenated blood for proper function. Depending on the degree of severity, signs of heart failure may appear while the dog is at rest, during mild exertion, or during moderate or extreme exercise.

In congestive heart failure, blood backs up in organs—usually the lungs but occasionally in the body’s other major organs—and causes the congested organs to function abnormally, become swollen with fluid, or both.

CAUSES OF HEART FAILURE

Several factors can contribute to the development of heart failure in dogs, including:

1. Valvular disease: The most common cause, particularly in small breeds, is chronic degenerative valve disease (CVD). This condition affects the heart valves, leading to leaks and inefficient blood flow through the heart.

2. Dilated Cardiomyopathy (DCM): This condition, often seen in larger breeds, causes the heart muscles to weaken and the heart chambers to enlarge, impairing the heart’s ability to pump blood.

3. Heartworm disease: This condition is caused by parasitic worms that live in the heart and blood vessels, leading to inflammation and damage to the cardiac structures.

4. Congenital disabilities: Some dogs are born with birth defects affecting the heart structure or function, which can lead to heart failure.

5. Arrhythmias: Abnormal heart rhythms that disrupt the heart’s ability to pump blood effectively and reduce blood flow to the tissues that need it.

6. Pericardial disease: Inflammation or fluid buildup in the sac surrounding the heart can restrict heart function.

7. Poisoning: Some poisons affect the heart, cause muscle damage or arrhythmias, and ultimately result in heart failure.

PRESENTATION OF HEART FAILURE

Signs associated with heart failure depend on the causes of the heart failure and the heart chamber that is affected. With left-sided congestive heart failure, the signs and symptoms are caused by a backup of pressure in the blood vessels delivering blood to the left ventricle of the heart. This causes fluid to accumulate within the lungs (called pulmonary oedema). Coughing, difficulty breathing, and exercise intolerance (fatigue with trouble breathing associated with exercise) are the most common signs. Some dogs with left-sided congestive heart failure faint due to lack of blood flow and oxygen to the brain. They may also have a low heart rate and low blood pressure and may collapse due to this. Dogs with leftsided congestive heart failure often breathe faster than healthy dogs. Your vet may ask you to count the number of breaths your dog takes within a minute when he is sleeping or resting. This sleeping respiratory rate can then be regularly monitored to identify early heart failure and assess whether your dog responds as hoped to treatment.

Right-sided congestive heart failure results in increased pressure in the blood vessels delivering blood to the right atrium of the heart and the body’s veins and capillaries. This may cause fluid to build up in the abdomen, the chest cavity, the liver and the limbs.

Biventricular failure  arises when both the right and left ventricles are not working correctly, such as in dogs with heart muscle failure resulting from dilated cardiomyopathy or poisoning. Signs attributable to both forms of congestive heart failure can be noted, although it is common for signs of either right or left congestive failure to outweigh the other.

SYMPTOMS OF HEART FAILURE

Recognising the signs of heart failure early can make a significant difference in managing the condition. Common symptoms include:

• Coughing: This is often worse at night or after exercise due to fluid buildup in the lungs.

• Difficulty breathing: Laboured or rapid breathing or shortness of breath.

• Exercise intolerance: Fatigue and weakness during physical activity.

• Weight loss: Loss of appetite and muscle wasting.

• Abdominal swelling: Due to fluid accumulation in the abdomen (ascites).

• Restlessness: Especially at night, as the dog struggles to find a comfortable position.

• Fainting or collapse: In severe cases, due to inadequate blood flow to the brain.

DIAGNOSIS

Prompt vet care is crucial if you suspect your dog may have heart failure. To diagnose the condition, your vet will typically do the following:

• A physical examination: Listening to the heart and lungs with a stethoscope to detect abnormalities.

• Chest X-Rays: To check for heart enlargement and fluid in the lungs.

• Echocardiogram: This is an ultrasound of the heart to assess its structure and function.

• Electrocardiogram (ECG): This test measures electrical activity in the heart and is used to detect abnormal heart rhythms.

• Cardiac biomarker blood tests: These tests detect proteins in the blood that increase with certain types of heart disease and failure.

• Other blood tests: To check for underlying conditions and assess overall health.

TREATMENT OPTIONS

It is important to treat heart failure to improve heart muscle performance, control arrhythmias and blood pressure, improve blood flow, and reduce the amount of blood filling the heart before contraction. If not controlled, all of these can further damage the heart and blood vessels. It is also necessary to reduce the amount of fluid in the lungs, abdomen, or chest cavity.

DRUGS

There are many types of drugs available for treating heart failure. The specific drugs, dosage, and frequency used will vary depending on the cause and severity of the heart failure and other factors. Your vet can best decide on the appropriate drugs for your pet. All medications a vet prescribes must be given to the animal as directed. Otherwise, they may not be effective and may even cause serious complications or harm.

Some of the drugs used include the following:

• Diuretics are usually prescribed for managing fluid overload.

• Pimobendan improves heart muscle contraction, dilates blood vessels, increases cardiac output, and reduces blood pressure in patients with congestive heart failure caused by atrioventricular valve insufficiency or dilated cardiomyopathy.

• Digoxin, part of a group of drugs known as positive inotropes, may be used to help the heart muscle contract in patients with certain arrhythmias.

• ACE inhibitors (ACE stands for angiotensin-converting enzyme) and vasodilators can widen blood vessels and thus lower blood pressure.

• Beta-adrenergic blocking drugs (also called beta-blockers) and calcium channel blockers are helpful in some cases of congestive heart failure.

NUTRITION

The overall nutritional goals for animals with heart failure include supplying adequate calories, reducing inflammation, balancing sodium, and supplementing any missing nutrients. Supplementation with omega-3 fatty acids may also help decrease inflammation and manage arrhythmias.

A low-sodium diet is frequently recommended for dogs with severe congestive heart failure that does not respond well to conventional treatment. In dogs with mild to moderate congestive heart failure, severe sodium restriction is not needed, but diets high in salt and human foods (‘table snacks’) should be avoided. Prescription diets tailored for these differing levels of sodium restriction are readily available, as are recipes for homemade salt-restricted diets. Sodium-free snacks should also be given in place of regular treats. Salt should not be restricted in dogs with heart disease that have no sign of congestive heart failure because this can result in the early activation of certain hormones that make the problem worse.

OTHER TREATMENTS

Dogs with severe left-sided congestive heart failure and fluid in the lungs (pulmonary oedema) may not get enough oxygen. Oxygen can be given through an oxygen cage, tight-fitting mask, oxygen collar, or nose tube.

Thoracentesis and abdominocentesis are procedures in which a needle is inserted into the chest cavity or abdomen, respectively, to withdraw excess fluid. It may be used to treat dogs with congestive heart failure that have an accumulation of fluid in these areas. The procedure can lead to rapid improvement in signs and can be performed regularly if needed.

REGULAR MONITORING

Regular vet check-ups and monitoring at home can help track your dog's condition and adjust treatments as needed.

LIFESTYLE ADJUSTMENTS

Moderate exercise, avoiding strenuous activity, and ensuring your dog has a stress-free environment can help manage symptoms.

PREVENTIVE MEASURES

While some causes of heart failure cannot be prevented, certain measures can reduce the risk:

• Regular vet check-ups: Early detection of heart issues can lead to better management.

• Heartworm prevention: Monthly heartworm preventatives can protect against this dangerous parasite.

• Weight management: Keeping your dog at a healthy weight reduces strain on the heart.

CONCLUSION

Heart failure in dogs is a serious condition, but with early detection, proper treatment, and ongoing management, many dogs can continue to live happy, comfortable lives. By understanding the causes, recognising the symptoms, and working closely with your vet, you can provide the best possible care for your canine companion.