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.
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 (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 (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 (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 (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 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.
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.