Heart Disease Awareness Week

This Valentine’s Week is Heart Disease Awareness Week. In this article, we will discuss the common types of heart disease and their associated symptoms in dogs and cats.

Heart disease is an increasingly common condition in pet dogs and cats, probably because their average life expectancy is increasing due to improved veterinary care. Some heart defects may be present from birth (congenital), but only show symptoms as your pet gets older, whilst other diseases develop later in life as a result of the effects of ageing or damage to the heart.

The heart is a muscular pump with four separate chambers. The right side sends blood to the lungs where it picks up oxygen, then the left side receives blood from the lungs and pumps it around the rest of the body. The chambers are separated from one another by a series of valves that ensure the blood can only flow in the correct direction through the heart.

Heart disease can affect any area of the heart
  • Heart Valves: The heart valves may fail to develop properly, e.g. Mitral Dysplasia, or may degenerate due to ageing (Endocardiosis), or the heart valves may also be affected by specific infections (Endocarditis). Abnormal valves result in leakage of blood between the heart chambers even when they are closed, which can be detected as a heart murmur when listening to the heart with a stethoscope, and may also be seen on ultrasound of the heart (echocardiogram).
  • Heart Muscle: Disease of the heart muscle can cause it to be either too thick or too thin. If the muscle is too thin, the heart cannot contract properly, and if it is too thick then the heart cannot relax properly, and so does not fill with blood between contractions. In both cases, the heart is unable to pump sufficient blood out.
  • Electrical Conduction: Abnormal electrical conduction affects the rate and rhythm of the heart, and can be caused by diseases outside of the heart. If this results in the heart beating too quickly, then there is not enough time for it to fill properly between beats, and so less blood is pumped with each beat. If the heart beats too slowly, then there are not enough pulses to supply enough blood to the body. Chaotic rhythms occur where contractions of different parts of the heart are not synchronised, and so pulse volume is reduced.
  • Pericardium: The pericardium is a strong sac that surrounds and supports the heart. Changes to the pericardium usually result in constriction of the heart, preventing it from filling properly between contractions. The right side of the heart (which has thinner walls) is usually more easily compressed than the left side. Diseases of the pericardium are very rare in cats.
Heart Disease in Dogs:

The two most common types of heart disease in the adult dog are Dilated Cardiomyopathy (DCM) and Valvular Heart Disease.

DCM is seen most commonly in large and giant breeds, particularly Dobermanns, Great Danes and Irish Wolfhounds. Some spaniels are also affected, but it may affect dogs of any breed. The disease causes stretching of the heart muscle walls so that the heart swells (like a balloon filled with water), and the contractions of the heart muscle become very weak so blood cannot be pumped around the body effectively.

Valvular Heart Disease is particularly common in Cavalier King Charles Spaniels, but can occur in any breed. The ageing process can cause the heart valves to become worn and degenerate, becoming more leaky. Instead of closing each time the heart pumps, the valves flop open allowing blood to move backwards as well as forwards through the heart chambers, resulting in a reduced blood supply to the body.

Heart Disease in Cats:

The most common forms of heart disease in adult cats are those affecting the muscle of the heart itself (Cardiomyopathy).

Hypertrophic Cardiomyopathy (HCM) is the most common cardiomyopathy in cats, and occurs when the heart muscle becomes abnormally thickened, preventing the heart from pumping properly as well as reducing the amount of blood that can flow through it. Hypertrophic Cardiomyopathy can be caused by an increased workload for the heart (such as cats with hyperthyroidism which causes an increased heart rate), as this causes the muscle to increase in size. Hypertrophic Cardiomyopathy can however, also occur in otherwise healthy animals with the exact cause often unknown. Certain breeds such as Persians may be predisposed, suggesting a genetic tendency.

Dilated Cardiomyopathy (DCM) is caused by stretching of the heart muscle walls so that the heart swells (as with dogs with DCM). It used to be seen in cats whose diets contain an insufficient amount of Taurine (a type of amino acid found in animal protein), but DCM in cats is now much less common as pet food manufacturers add extra taurine into their cat foods.

Puppies and kittens may be born with heart defects (congenital heart problems), because the heart does not develop normally. The most common problems are leaky valves and holes inside the heart that allow blood to flow in abnormal directions.

In humans, heart disease is usually the result of damage to the heart muscle caused by blood clots (Myocardial Infarction), which causes the signs of a heart attack. Cats and dogs however, do not get this type of heart disease.

Signs of heart disease

In dogs, signs of heart disease are often very similar, whatever the cause, but may often be confused with natural ageing changes. Reduced energy and less desire to exercise (lethargy) are common, and severe heart disease may cause a poor appetite and weight loss. Weight loss might not be obvious however, if heart failure results in water retention. Other common signs of heart failure are panting and coughing due to fluid build-up in the lungs, and less commonly, dogs with heart disease may faint or collapse.

Cats are “Masters of Disguise” – they are very good at concealing ill health and there may be no evidence of any problem until the condition is very advanced. Many of the effects of heart disease are similar to ageing changes, such as poor appetite, low energy levels, reduced activity and longer rest periods. You may notice your cat’s tongue or gums turn a bluish tinge (cyanosis) as a result of oxygen starvation, and an increased breathing effort may occur if fluid starts to build up in the lungs or chest.

Sometimes the first signs of heart disease in cats are fainting episodes or seizures. Panting, weight loss, restlessness, coughing, fainting and water retention causing swelling of parts of the body – are signs of very severe heart disease, and are not normally seen until the condition is advanced. Heart disease can be associated with increased blood pressure (hypertension), that can cause blood vessels to burst. If the blood vessels in the eye are affected, then your cat may go blind.

In some cats, blood clots can form within the heart if it is not functioning properly. Fragments of these clots can break off into the circulation and cause a blockage in one of the blood vessels. Aortic thromboembolism or “Saddle” Thrombus, occurs when a blood clot cuts off the blood supply to the back legs, and can cause sudden paralysis. This condition is very painful, and cats be found unable to walk and very distressed. This is an acute emergency, requiring immediate veterinary treatment, but sadly many cases cannot be resolved.

If you are concerned your cat or dog may be showing any signs of heart disease, please contact the surgery to arrange an examination by one of our vets.