Congestive Heart Failure in Dogs
What is congestive heart failure?
Congestive Heart Failure (CHF) is a term that refers to the heart’s inability to pump adequate blood to the body. There are many causes of CHF in dogs. The two most common causes are mitral valve insufficiency (MVI), or a leaky mitral valve, the valve between the left atrium and the left ventricle and dilated cardiomyopathy(DCM). Clinical signs vary depending on whether the dog has left- or right-sided heart failure. The most common symptoms of congestive heart failure are decreased stamina, coughing or difficulty breathing.
What is the difference in the signs?
In left-sided congestive heart failure (LS-CHF), when the heart contracts or pumps, instead of the left ventricle pushing the blood into the systemic circulation, some leaks through the mitral valve back into the left atrium and then it backs up into the lungs. Fluid then seeps into the lung tissue resulting in pulmonary edema. This causes coughing and difficulty breathing. Left-sided congestive heart failure (LS-CHF) is the most common form of congestive heart failure. The classic signs of heart failure – coughing and fluid in the chest – are most commonly caused by LS-CHF.
Right-sided congestive heart failure (RS-CHF) causes poor venous return to the heart. In other words, when the heart contracts or “pumps”, instead of the right ventricle pushing the blood through the lungs for oxygenation, some leaks through the tricuspid valve (the valve between the right atrium and right ventricle) back into the right atrium. This blood backs up into the systemic circulation (the main circulation of the body) and consequently becomes “congested”. Fluid accumulates in the abdomen, interfering with the function of the organs in these areas. The abdomen may fill with fluid, a condition called ascites. Fluid may also leak from veins in the limbs, causing swelling, known as peripheral edema.
Is CHF due mainly to heart valve disease?
CHF is most commonly caused by valvular insufficiency. It is estimated that 80% of the canine CHF cases are caused by MVI. However, there are many other causes. Disease of the heart muscle (cardiomyopathy), irregularities of rhythm and narrowing of some of the major blood vessels can also cause CHF. Initially, MVI results in LS-CHF. If left untreated, the heart failure may progress to involve both sides of the heart.
What clinical signs should I expect?
The most common clinical sign of congestive heart failure (CHF) is persistent coughing accompanied by difficulty breathing. This is due mainly to pulmonary edema or the accumulation of fluid in the lungs. The enlarged heart will also push against the trachea, causing irritation that can induce a cough. Many dogs with CHF will fatigue more easily, have reduced stamina and not engage in playing or walking as they once did. Coughing when at rest or sleeping, excessive panting, persistent loss of appetite, a swollen belly, and pale or bluish gums are also signs associated with heart failure. The dog will develop generalized weight loss and muscle wasting due to the effects of CHF on other body systems. If any of these signs develop in a pet with a heart murmur, notify your veterinarian immediately.
Do dogs have heart attacks?
In humans a “heart attack” usually refers to myocardial infarction (MI). Myocardial infarction refers to death of the cells in an area of the heart muscle or myocardium. Cell death is usually due to oxygen deprivation caused by obstruction of the coronary blood vessels that supply blood to the heart muscles. “Heart attacks” are rare in dogs but unexpected and sudden death in dogs diagnosed with any form of heart disease is possible.
How is CHF diagnosed?
As with any heart problem, diagnosis involves several tests:
Auscultation or listening to the heart with a stethoscope is the first step in diagnosing heart disease. Heart murmurs are detected by auscultation; the murmur’s location and intensity helps determine its significance. The heart rhythm is assessed, and if there are concerns, the veterinarian may simultaneously palpate or feel the pulse to determine its strength and rhythm. Finally, the lungs are assessed, looking for evidence of changes associated with heart failure.
Chest x-rays are taken to evaluate the size and shape of the heart and look for lung changes such as the presence of fluid.
Blood and urine tests are performed to give an indication of any other disorders in the body. Liver and kidney function are often impaired in patients with heart disease.
An electrocardiogram (ECG) measures the electrical activity of the heart and allows accurate determination of both heart rate and rhythm. Any abnormal rhythms (arrhythmias or dysrhythmias) can be detected and evaluated.
Ultrasound examination (echocardiogram) utilizes ultrasound waves to evaluate the heart. The size and thickness of each heart chamber can be evaluated, and the effectiveness of the heart’s contractions can be directly observed. Measurements can be taken to evaluate the heart’s pumping efficiency.
Can’t you treat my dog without these tests?
Accurate diagnosis gives us a much better guide to the type and extent of treatment necessary. Today there is a wide selection of heart medications that can be used to treat congestive heart failure and treatment regimes must be tailored for each patient. Without these tests, your veterinarian is unable to determine the optimal treatment for your pet, and may inadvertently cause more harm than good. With proper treatment, many dogs are able to live a normal life for many months to years.
Cardiomyopathy (Heart Disease) in Cats
Cardiomyopathy is the name given to any disease affecting the heart muscle itself. This is the most common form of heart disease seen in cats, and the most common cause of heart failure. Disease of the heart valves (causing ‘leaky’ valves which prevent the heart functioning normally) are an important and common cause of heart disease in humans and in dogs, but this is rarely seen in cats.
Cardiomyopathies are described according to the effect they have on the structure and function of the cardiac (heart) muscle. The main classification is to divide the disease into:
- Hypertrophic cardiomyopathy (HCM) – this is the most common form of heart disease in cats and occurs where there is an increase in the thickness of the muscular wall of the heart. This reduces the volume of blood within the heart and also prevents the heart muscle relaxing properly between contractions.
- Dilated cardiomyopathy (DCM) – this is where the muscular wall of the heart generally becomes thinner than usual, the heart enlarges, and the heart muscle cannot contract effectively.
- Restrictive cardiomyopathy (RCM) – here primarily there is fibrosis of the wall of the heart, making it stiff and inelastic, so preventing the heart chambers filling normally.
- Intermediate cardiomyopathy (ICM) – these cases have changes consistent with more than one type of disease – for example a mixture of both hypertrophy and dilatation present.
Underlying causes
Although in the majority of cases of heart disease in cats the underlying cause is unknown, there are various potential recognised causes, and your vet may need to investigate some of these. Known potential underlying causes include:
Cardiomyopathy secondary to other diseases
- Hyperthyroidism (overactive thyroid glands)
- Hypertension (high blood pressure)
- Acromegaly (excessive growth hormone production)
Exposure to toxins
- Some drugs may have secondary effects on the heart
Hereditary causes
- Genetic defects have been recognised in Maine Coon cats and other breeds that may contribute to development of cardiomyopathy
Nutritional causes
- Taurine deficiency (causing dilated cardiomyopthy)
Infiltrative of the heart muscle
- Lymphoma (a type of malignant tumour)
What happens in cardiomyopathy?
In cardiomyopathy, the underlying abnormality of the cardiac muscle leads to a compromise in cardiac function. The alteration in heart function depends on the type of cardiomyopathy though:
- With HCM and RCM – the disease mainly interferes with the ability of the heart muscle to relax properly between contractions. The relaxation phase between each cardiac contraction is called diastole, and if this does not occur properly, the heart cannot fill with blood so effectively. If severe, this will lead to heart failure, and a form known as ‘diastolic heart failure’.
- With DM – the disease mainly affects the ability of the heart muscle to contract (called ‘systole’). This will compromise the ability of the heart to pump (and eject) blood. In severe cases this too leads to heart failure – a form known as ‘systolic heart failure’.
Early signs of heart disease
In the initial phase of disease, cats may show no signs at all and appear completely normal. In fact a number of cats with cardiomyopathy may never actually develop clinical disease. However, while in some cats, progression of the underlying disease is slow, in others it can be quite rapid.
Some early signs of heart disease may be detectable during a clinical examination by your vet, prior to the onset of any overt signs. This is one of the reasons why every cat should be checked at least once a year by a vet (and ideally more often in older cats). Early warning signs that your vet might detect include:
- Presence of a heart murmur – this is an abnormal noise your vet can detect when listening to your cat’s heart with a stethoscope and develops due to turbulence in the flow of blood through the heart.
- Presence of a gallop rhythm – during each cycle of heart contractions, normally you can hear two sounds when you listen to the heart with a stethoscope (these sounds are associated with closure of heart valves during contraction and relaxation of the heart). With significant heart disease, a third audible heart sound is sometimes detected and this is referred to as a ‘gallop sound’ or ‘gallop rhythm’.
- Abnormalities in heart rate – with heart disease, the heart rate can sometimes significantly increase or decrease outside of the normal range for a cat, and sometimes there may be heart beats without any effective flow of blood (a heart beat but no pulse detectable in an artery (known as a ‘pulse deficit’).
- Presence of cardiac rhythm disturbances – these are also referred to as cardiac dysrrhythmias. Normally, cats have a very regular heart rate, but in heart disease there can be interference in the normal electrical impulses that control heart contractions and this can lead to disturbances to the to the normal rhythm.
Many cats, especially with early disease, may only have changes in the cardiac muscle that are detected on an ultrasound examination of the heart. These cats are clinically silent (or asymptomatic), although many will go on to develop signs later on.
Heart failure
If heart function is significantly impaired by cardiomyopathy, this will lead to heart failure, where there is compromise to blood flow through the heart and blood output from the heart.
Cats can sometimes develop clinical signs without prior warning, and some cats can deteriorate very rapidly. Some cats with heart disease show signs of collapse, or ‘fainting’. However, this is relatively uncommon and usually associated with marked disturbances to the normal rhythm of the heart (which can lead to episodes where the brain is starved of oxygen through poor blood flow).
Unlike dogs, cats are not exercised in the same way (eg, taken for walks on a lead) so it is often much more difficult to detect that they have reduced exercise ability – often an early sign of heart disease. Cats are likely just to spend a little more time resting or sleeping and this may not be very obvious. Because detecting early disease (especially without an examination by your vet) is often difficult, and cats are good at hiding signs of disease, there may be no obvious signs until a ‘critical point’ is reached due to advance of the disease or perhaps when the cat becomes stressed, that may result in sudden or rapid development of quite marked signs.
In cats, the most common sign of heart failure is the development of difficult breathing (called dyspnoea) and/or more rapid breathing (called tachypnoea). This is generally caused by either a build up of fluid in the chest cavity around the lungs (called a pleural effusion), or due to a build up of fluid within the lungs themselves (called pulmonary oedema).
Along with breathing difficulties, cats may have cold extremities (eg, ears and paws), and may have pale mucous membranes (gums and eyes) suggesting poor circulation. Occasionally the mucous membranes of the mouth and eyes, and even the skin, may show signs of cyanosis (a bluish colour). Coughing is rarely seen in cats with heart disease, although it is quite common in dogs. In cats, when coughing is seen, this is much more likely to be caused by a disease of the airways (such as bronchitis).
Feline aortic thrombeombolism (FATE)
Another sign which can occur in cats, and may sometimes be the first indicator of underlying heart disease, is the development of what is known as ‘feline aortic thromboembolism’ or FATE. A thrombus (blood clot) may develop within one of the heart chambers (usually left atrium) in a cat with cardiomyopathy. This occurs mainly because the blood is not flowing normally through the heart. The thrombus, or clot, is initially attached to the wall of the heart, but may become dislodged and be carried into the blood leaving the heart. A thrombus that moves into the blood circulation is called an embolus, hence the term ‘thromboembolism’. Once in the circulation, these emboli can lodge in a small artery and obstruct the flow of blood to a region of the body. Although this can happen at a number of different sites, most commonly this happens towards the end of the major artery that leaves the heart (the aorta) as it divides to supply blood to the back legs. This complication is seen most commonly with HCM, and will cause a sudden onset of paralysis to one or both back legs, with severe pain and considerable distress.
Differentiation of forms of cardiomyopathy
Various diagnostic tests can be done to assist the diagnosis of heart disease in cats.
- Heart ultrasound (echocardiography) – is very helpful as it allows a view of the internal dimensions of the heart, the wall thickness, and the contractility of the heart to be assessed. It can also show where a heart murmur is originating from. This is the only test which can readily distinguish between different types of heart disease in cats. Although a small area of skin usually needs to be shaved to perform ultrasound, the procedure is not uncomfortable or painful and so can be performed in most cats without any sedation or anaesthetic.
- Tests for underlying disease – may need to be performed in some cases, including blood tests and blood pressure measurement.
- Electrocardiogram (ECG) – this is an electrical trace of the heart activity. It can be very useful for the detection of cardiac rhythm disturbances, but has more limited use beyond that.
- Radiography (X-rays) – are helpful for showing changes in the overall shape and size of the heart, and for detecting a build up of fluid (pulmonary oedema or pleural effusion). Repeating radiographs may also allow monitoring of the efficacy of any treatment.
Treatment
The underlying cause of the cardiomyopathy can only rarely be treated, but if it develops secondary to taurine deficiency in the diet (which can be a cause of DCM), or secondary to things like hypertension (high blood pressure) or hyperthyroidism (overactive thyroid gland), then treating the underlying disease may improve cardiac function.
Where heart failure develops, various drug treatments may be available to help improve and manage the condition. These may include drugs such as:
- Beta-blockers such as atenolol or propranolol, which slow down the heart rate and reduce the oxygen demand on the heart.
- Diltiazem – this drug is known as a ‘calcium-channel blocker’, and reduces both heart rate and the strength of heart contractions. It reduces the oxygen demand of the heart and may help the heart muscle to relax between contractions
- ACE-inhibitors (angiotensin-converting enzyme inhibitors, e.g., benazepril, ramipril, enalapril) or ARBs (angiotensin receptor blockers, e.g., telmisartan) – help block the activation of the renin-angiotensin-aldosterone system (RAAS) – a hormone system stimulated in cats with heart disease. Their use may help in the management of heart failure and possibly also in earlier stages of heart disease.
- Pimobendan – is drug known as a calcium channel sensitiser. It increases the strength of the contraction of the heart and also acts to dilate blood vessels which may help the flow of blood. It has been used in some cats with congestive heart failure.
- Diuretics (such as frusemide/furosemide) – these are extremely valuable once signs of congestive heart failure develop, to help remove the fluid build up in or around the lungs. The dose of these drugs can be adjusted over quite a wide range to achieve the desired result.
Unfortunately the true effectiveness of many drugs in treating heart disease in cats is unknown, and more clinical trials are needed. Different drugs also act in different ways, and so may be helpful in different situations. In general, diuretics are the most useful drugs to manage the signs of congestive heart failure, but with early diagnosis of heart disease treatment may help to slow or delay its progression and maintain a good quality of life.