Feline Heart Disease

Heart disease in domestic cats is actually quite common, which may come as a surprise to feline owners. It can strike any age or any breed of cat. One of the most challenging aspects of feline heart disease is that cats may not show any warning signs (such as exercise intolerance, coughing, weakness)until the process is very advanced. This means that a cat can literally be playing vigorously one day, and suddenly have trouble breathing. Untreated heart disease often progresses to heart failure, blood clot formation, and death.


The detection of a new heart murmur by your veterinarian (often on routine examination) can be the first sign that changes in the heart have taken place. While not every murmur signals the onset of heart disease, a further investigation is warranted since those murmurs which are a result of heart disease cannot be distinguished from "innocent" murmurs by routine tests alone.


Fortunately, advances in companion animal medicine enable veterinarians to efficiently diagnose cardiovascular disease in cats, even in its early stages. In many instances, if heart disease is detected prior to the stage of actual heart failure, it can be successfully controlled with medication(s). A feline with carefully controlled heart disease may live symptom-free for years!



-- TESTING FOR HEART DISEASE --

The first test for heart disease begins with a thorough physical examination. During the exam, the veterinarian will determine your cat's heart rate and rhythm. A persistently elevated rate, or a rhythm that is irregular can be associated with heart disease in cats. The presence of a murmur (especially one not previously detected) may be further evidence of heart disease. In advanced cases of heart disease, abnormal sounds in the lungs may be heard. A weak or irregular pulse can also occur. The results of the physical exam may lead to further testing.


Chest Radiographs (x-rays)

Chest radiographs are important components in the diagnosis of feline heart disease. A diseased heart will most often enlarge over time. In advanced stages, fluid may be detectable in the chest cavity (pleural effusion) or in the lungs themselves (pulmonary edema).


Electrocardiogram (EKG or ECG)

An electrocardiogram (EKG or ECG) is a tracing of the electrical activity of the heart. It documents heart rate and rhythm. In addition, subtle changes can occur in the shape of the ECG spikes that can reveal certain types of pathological changes in the heart. It is a rapid and painless test that can be performed in the veterinary office.


Echocardiogram

An echocardiogram, also known as a cardiac ultrasound exam, is one of the most advanced and sensitive tests for determining the presence of heart disease in animals. It is painless and generally does not require sedation. The technique uses sound waves to actually visualize the heart in action. From this exam, the dimensions of each heart chamber can be determined.


Ultrasound can also detect the presence or absence of fluid in the sac around the heart (pericardial effusion), fluid in the chest, congenital heart defects, abnormalities of the heart valves, blood clots within the heart itself, or heart tumors (rare in cats). Most importantly, the echocardiogram can actually determine the type and degree of heart dysfunction. An accurate assessment of heart disease is paramount to effective treatment.



--TYPES OF FELINE HEART DISEASE--

Dilative cardiomyopathy

Dilative cardiomyopathy denotes heart disease that results in an enlarged heart with thinning and weakening of its muscular walls. The weakened heart cannot pump efficiently which subsequently can lead to fluid accumulation in the lungs and/or chest cavity (analogous to congestive heart failure in humans). Enlargement of the heart can lead to leakage at the heart valves, creating a murmur.

This form, although more difficult to successfully control, has become less common in recent years. A few years ago, research showed that deficiency of the amino acid taurine in the feline diet was one of the main causes of dilative cardiomyopathy. Since that time, most commercially made feline diets are supplemented with taurine.


Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is the most commonly diagnosed heart disease in cats. The walls of the heart become much thicker and stiffer than normal. This results in a smaller chamber to hold the blood, and diminishes the amount of blood pumped out with each beat. Consequently, the heart has to accelerate and use more energy to accomplish its original task. The geometric changes in the heart can lead to leakage at the valves, and development of a murmur. As the disease progresses, the heart can become so thickened that it cannot pump the blood forward at an adequate rate. This usually results in fluid accumulation in the lungs.

The cause in most cases is unknown, but genetics are thought to play a role in at least some cat breeds. While it is most common in middle-aged male cats, it can be seen in either sex as early as 6 months of age. Hypertrophic cardiomyopathy remains the most treatable form of feline heart disease.


Restrictive cardiomyopathy

Restrictive cardiomyopathy is a less common, less defined type of heart disease in cats. It is more difficult to detect, as many cats will have near normal echocardiograms, but their heart walls seems "stiffer" and less efficient at pumping blood forward. It is thought that in such cats the heart wall muscle cells become slowly replaced with less functional scar tissue. Cats with this type of disease may shows signs consistent with either dilative cardiomyopathy, hypertrophic cardiomyopathy, or both.




--THERAPY FOR FELINE HEART DISEASE--


Therapy for feline heart disease depends on which type is diagnosed and how advanced the disease is. As previously mentioned, cats with hypertrophic cardiomyopathy have the best long term outlook The most serious consequences of progressive heart disease are weight loss, anorexia, difficulty breathing, weakness, and blood clot formation (with possible limb paralysis). Cats with advanced heart disease are at risk for sudden death.

Early detection and intervention, however, can be very rewarding for many cats and their owners.



Furosemide

Furosemide (Lasix‰) is a diuretic ("water pill") used in all types of feline heart disease. It reduces the volume of fluid that the heart has to pump, and removes fluid from the lungs. This makes the heart's work easier.


Enalapril

Enalapril (Vasotec¨ or Enacard‰) is a drug known as a vasodilator. It is very useful in many types of heart disease. It lowers blood pressure and reduces the workload of the heart. In dilating the vessels downstream from the heart, it lowers the resistance to blood being pumped forward.


Diltiazem

Diltiazem (Cardizem‰) is a drug used in humans and animals. It is a "calcium channel blocker." Most commonly used for hypertrophic cardiomyopathy, it reduces the stiffness and work of heart walls. It has been documented to prevent or reverse wall thickening in many cats, and is very well tolerated.


Digitalis

Digitalis (Digoxin® or Lanoxin®) is a very old but useful drug utilized in people and animals mainly for treatment of dilative cardiomyopathy. It strengthens the contraction of the heart muscle with the goal of improving pumping function. It also can correct certain types of irregular heart rhythms. Because it has a narrow safety range, the drug concentrations in the patient's bloodstream must be monitored periodically.


Betablockers

Betablockers such as propranolol (Inderal®) or atenolol (Tenormin®) are prescribed mainly for hypertrophic cardiomyopathy. These drugs slow the rhythm of the heart, allowing the attenuated chambers to fully fill with blood between heartbeats. This increases cardiac output and thus reduces the actual work of the heart. Betablockers also lower blood pressure and regulate heart rhythms.


Aspirin

One of the health risks for feline heart disease patients is the formation f a blood clot in the heart. The clots can form in the enlarged heart chambers where the blood undergoes increased turbulence. If a piece of the clot leaves the left side of the heart and travels downstream, it often lodges in the large blood vessel known as the aorta. Since the aorta is the trunk artery carrying blood to the back half of the body, loss of this blood flow can cause temporary or permanent paralysis. The best prevention of this complication is to 1) adequately control the heart disease and reduce heart chamber size and 2) low dose aspirin therapy. While cats can have toxic or lethal reactions to high dose aspirin or any dose of acetaminophen (Tylenol®), low dose aspirin can often be used safely. The usual dose is 1/4 of an adult regular aspirin or 1 baby aspirin (81 mg.) per cat TWICE WEEKLY.

Congenital Heart Disease


Your pet was born with a congenital heart defect. Congenital defects are abnormalities that occur in the developing fetus and are usually recognized soon after birth. If the defect is too sever, the embryo dies before birth. Other situations, not as sever, allow embryo development to birth, and the pet can live until the defect interferes with normal functioning (here, the cardiovascular system). Most congenital defects are first recognized at or near the time of weaning when the pet is taken to the veterinarian for a first examination. Sometimes these problems may not be identified until later in life. Congenital defects are most often the result of abnormalities in the genetic makeup of the pet. The abnormal genes may or may not be present in other members of the litter but are carried by the mother and/or father, sometimes without compromising their health. Other causes of congenital defects include exposure to radiation, toxins, or physical events that occurred during the animal's embryonic stage.

There are numerous ways to classify congenital heart defects, but for simplicity we will consider them in four major categories: (1) obstruction of blood flow within the heart: (2) abnormal communication between the two sides of the heart, increasing the blood flow from the left (systemic) to the right (lung) side of the heart: (3) abnormal communications sending blood in the opposite direction of flow, from the right (lung) to the left (systemic) side of the heart: and (4) vessel (vascular) abnormalities that obstruct a body part and interfere with normal function.

Obstruction of blood flow within the heart includes conditions such as pulmonic, mitral, or aortic valvular stenosis. Valvular obstruction is caused by a narrowing of an area of blood flow, decreasing circulation from the heart to some part of the body. These conditions vary from mild to severe. They may be minimal and require no care. However, in other cases, medication only, opening the obstruction with a special catheter, or surgical correction may be needed. Surgery, although commonly performed in humans, is both difficult and infrequent in veterinary medicine.

Blood may flow abnormally from the left to the right side of the heart because of a hole between the two sides of the heart that did not close during embryonic formation. One such condition, patent ductus arteriosus (PDA), is a remnant of normal embryonic heart function. If PDA is diagnosed early, it may be corrected surgically and the pet may be able to lead a normal life. Other conditions such as ventricular or atrial septal defects involve a hole between two chambers of the heart. Closure of septal defects requires open heart cardiopulmonary bypass surgery, which is infrequently performed in veterinary medicine. Blood flow from the right to the left side of the heart without passing through the lungs is very abnormal and quite uncommon. Thus, a serious communication problem exists that results in unoxygenated blood being transported to the body. Such a situation usually does not allow the pet to live beyond early adulthood. Because of the complicated nature of these problems, open heart surgery is rarely an available option. Surgical procedures may be available at teaching and specialty clinics to treat such problems.

Persistent aortic arch, peripheral arteriovenous shunts, and cor triatriatum are heart problems that are the result of abnormal vessels interfering with normal blood flow. These conditions can usually be corrected surgically if identified early, before complicating problems develop to preclude normal life.

Because many congenital heart defects are thought to be due to genetic problems that can be passed from one generation to the next, veterinarians recommend that animals with such conditions be neutered at an early age to prevent breeding and the dissemination of defective genes to a new generation. Some congenital heart defects may be surgically corrected; others are effectively dealt with for variable periods using medications. Regrettably, most congenital heart defects have a poor long-term prognosis. It is sad for the owner and for the pet to suffer needlessly. In selected circumstances, euthanasia may be recommended if the pet is unable to maintain a good quality of life.

A congenital heart defect is suspected after a thorough physical examination has been performed. The electrocardiogram helps to identify the presence of abnormal heart chamber size as well as irregularities of the heart's rate and/or rhythm. Radiographs (x-rays) are needed to visualize abnormalities in the size and appearance of the heart, vessels, and lung structures. The ultrasound (echocardiogram) examination is a direct, noninvasive means of looking inside the heart's walls to measure the size of the heart's four chambers and to identify abnormalities (qualitatively and quantitatively) in blood flow. Occasionally, more invasive procedures such as cardiac catherization (passing small tubes into the heart and blood vessels and injecting dye) or surgical evaluation may be recommended.

 

SOURCE: Textbook of Veterinary Internal Medicine, Client Information Series, by Stephen J. Ettinger.

 

Canine Valvular Insufficiency and Congestive Heart Failure


An electrocardiogram (ECG) can identify heart enlargement or irregularities of the heart's rhythm. Radiographs (x-rays) can demonstrate heart enlargement and/or inappropriate fluid accumulation. Blood testing can identify hormonal, kidney or other internal medical problems. An ultrasound examination (echocardiography) accurately pictures enlarged heart chambers, abnormalities

Valvular insufficiency occurs when damaged and thickened valves develop within the heart of small and midsize dogs. Valve problems are unusual in larger breed dogs and in cats but they may develop. In the small breeds of dogs, valvular insufficiency begins in midlife and progresses slowly. The disease is associated with thickening and shortening of the valve components that separate the upper (atria) from the lower (ventricles) parts of the heart. Remember, normally blood flows in only one direction. If the valves fail to close completely when the heart contracts, blood moves forward but some leaks backward. Clinical signs vary depending on whether the right and/or left side of the heart is affected and whether heart enlargement presses on the windpipe. Fluid accumulates when the heart fails to pump enough blood to the body and instead the blood is transmitted backward from the heart to the lung or body.

Owners of pets with valve problems see inappropriate panting, heavy breathing, diminished exercise ability, fatigue, cough, and occasionally fainting. The cough usually starts at night and progresses to daytime as well, particularly when associated with exercise. Retching and nonproductive gagging follow the cough. When the right side of the heart is affected fluid may accumulate around the lungs, making it difficult to breathe, and in the abdomen, making it swell.

A number of treatments are used for pets with valvular heart disease, including exercise restriction. Walking is good exercise. Digitalis is a medication used to strengthen the heart and to treat some irregularities of its rhythm. It maintains a slower and more effective heart muscle contraction. Signs of digitalis excess include loss of appetite, lethargy, vomiting, and diarrhea. ECG monitoring permits the veterinarian to supervise your pet's progress. Diuretic agents are commonly given to remove excess water accumulation from the body and can cause increased water drinking and urination. Diuretics can induce weakness, dehydration, and blood salt abnormalities. Alterations in electrolytes (salt) levels are identified through periodic testing of your pet's blood. Angiotensin-coverting enzyme inhibitors (ACEI 's) are drugs that improve the bodies ability to reduce salt and water retention, to reduce high blood pressure, and to limit the effect of hormones that adversely affect heart muscle. Given in excess, ACEI drugs cause malaise, blood salt disturbances, loss of appetite, and possibly kidney damage. Antiarrhythmic agents may be given to stabilize the cardiac rate and rhythm. Drugs to decrease blood pressure and nutritional supplements may be required for specific conditions.

In order to control the symptoms of heart failure, low-salt (sodium) diets may be suggested. Excess sodium is normally removed by the kidney, but this does not occur as effectively in heart failure. Commercial low-salt diets, varying from moderate to extreme restriction, are effective in preventing salt and water retention. These diets are recommended only after heart failure has been diagnosed. A modest reduction in salt intake may be indicated before the onset of heart failure. If your pet refuses to eat a commercial diet, low-salt foods can be prepared by the owner under veterinary direction. It is important to emphasize that mixing low-salt diets with regular (high-salt) diets or feeding snacks high in sodium is not recommended.

Longevity and quality of life in dogs with this disease vary with the severity of the valve damage and the amount of blood leakage into the upper chambers of the heart. Concurrent medical conditions, age, and the physical status of the pet play a large role in determining the animal's prognosis. Clinical signs are progressive, and although they may be decreased, they never entirely resolve. Medical therapy can enhance the quality of life of the pet as well as increase life expectancy. Dogs with left-sided valvular heart disease treated with medication and a low-salt diet have an average life expectancy of about 9 months from the time heart failure begins. Abdominal fluid accumulation and body emaciations are signs of right-sided heart failure. Regularly removing the extra fluid may increase life expectancy. Surgical replacement of the valves is not an option in dogs at this time.

 

Source: Textbook of Veterinary Internal Medicine, Client Information Series, by Stephen J. Ettinger