Diseases of the heart can be broadly separated into two forms - congenital and acquired - but the specific types of disease that we see in small animal veterinary medicine are extremely varied. Dogs get different diseases from cats, and certain breeds of dogs get different diseases than other breeds. There are even breed specific cardiac diseases in cats.
Congenital heart disease is the term used to describe heart disease that is present at birth. A congenital defect, or combination of defects, occurs as a malformation of any valve, heart chamber, or great vessel, or involves abnormal connections between the heart chambers. The most common congenital heart diseases in dogs include patent ductus arteriosus (PDA); pulmonic stenosis (PS), and subaortic stenosis (SAS). These are all potentially inherited defects, there are certain breeds we know are predisposed to each, but any pup can be affected. We listen very closely to your puppy's heart beat when he comes in for his first examination because these conditions are typically first identified when a murmur is noted on physical examination during one of the first routine vaccination visits. A murmur is turbulent blood flow that creates vibrations which can be heard when a stethoscope is used to listen to the heart sounds. Not every murmur heard during a puppy wellness exam should be a source of major concern though, as innocent and physiologic murmurs are quiet and not associated with a heart defect. They are simply an abnormal sound in a normal functioning heart and commonly resolve by 16 weeks of age. Congenital heart defects typically produce loud murmurs that persist or become louder over time, so we will listen carefully each time your puppy presents for a round of booster shots. If a congenital heart defect is suspected, we will most often refer you and your puppy to a board certified cardiologist at the University of Tennessee for further evaluation.
Much more common than congenital defects are acquired conditions that we see as dogs age. By far, the most common heart condition we see is endocardiosis or a thickening of the valves of the heart which occurs as an aging change in many small and tiny breed dogs. These dogs will also present with a murmur heard on routine examination if we catch it early, or they may come in complaining of a cough, particularly at night or on first arising in the morning. The owner may note a change in breathing pattern or a decrease in exercise tolerance. We can confirm this diagnosis with a complete cardiac work-up in-house which includes chest x-rays, echocardiogram, electrocardiogram (if deemed necessary), a blood pressure evaluation, and blood tests. These dogs are treated medically, their specific needs determined by the results of the testing, and monitored on a regular basis for life. They often do extremely well for several years after diagnosis, although they may need to be on multiple medications as time goes on and this progressive degenerative condition worsens and their hearts enlarge. This is a disease we can not cure, but we can control symptoms, often for quite some time.
Another variety of acquired cardiac disease we see in veterinary medicine is cardiomyopathy, an abnormality of the muscle that makes up the heart wall itself. In these cases, there is not a problem with the valves separating the chambers of the heart, but the heart wall structure itself becomes less effective at beating properly. The most common form of canine cardiomyopathy is called Dilated Cardiomyopathy (DCM) and occurs primarily in large and giant breed dogs. The Doberman Pinscher, the Great Dane, the Boxer, and the Cocker Spaniel are significantly over-represented in cases of DCM. In these cases, the heart muscle actually becomes flabby and thin, and the heart becomes large and abnormally round. The muscle becomes progressively less effective at pumping the blood throughout the body, arrhythmias can result, and sometimes the first symptom we see is an acute death. More commonly, the ability of the heart to serve as a pump is gradually diminished, and clinical signs of DCM occur secondary to either decreased delivery of oxygenated blood to the body (lethargy, weakness, weight loss, collapse), or to congestion of blood in the lungs (coughing, increased respiratory rate and/or effort, abdominal distention) or both.
At Fountain City Animal Hospital, DCM is diagnosed by echocardiography, which demonstrates the chamber dilation and indices of decreased pump function characteristic of the disease. Thoracic radiography (chest x-ray) is useful to evaluate pulmonary (lung) tissue and vessels, and may show evidence of fluid accumulation in the lungs (pulmonary edema) or around the lungs (pleural effusion). Electrocardiography may be used to characterize heart rhythm and to rule out arrhythmias; and in some cases, a 24 hour electrocardiogram (Holter monitor) may be recommended to more accurately characterize cardiac rhythm. We treat DCM medically, based on the results of all of our testing, and medical therapy may provide significant improvement in lifespan and quality of life in affected dogs. Nonetheless, Canine DCM can be a devastating disease, and the prognosis for dogs with DCM is variable depending upon breed and status at presentation.
Cats can also get cardiomyopathy, but hypertrophic cardiomyopathy is the most commonly seen cardiovascular disease in cats. Instead of the gradual thinning of the heart walls as seen in canine DCM, in cats with HCM (hypertrophic cardiomyopathy), the walls of the heart become progressively thicker and thicker. The thickening of the heart mainly affects the left ventricle, the chamber that pumps blood out through the aorta to the rest of the body. This results in a cascade of events, eventually leading to the development of congestive heart failure. Although there are specific conditions that can cause the heart muscle to become thicker (such as hyperthyroidism and high blood pressure), HCM is considered to be a primary disease because an identifiable disease process cannot be found.
Cats of either gender and almost any age can be affected by HCM, but most commonly we see it in young male cats. The clinical signs of HCM can vary greatly from cat to cat. Some cats present with very non-specific signs, such as lethargy, inappetence, weight loss, hiding, and reluctance to socialize with the owner and with other cats. Coughing occurs occasionally but is fairly uncommon, especially when compared to dogs with heart disease. In most cases a cat has no clinical symptoms, but we will hear an abnormal rhythm or murmur when listening to an affected cat's chest. This is our preferred method of finding HCM, rather than being presented with a cat in heart failure or with the devastating complication of HCM that occurs when a blood clot (also known as a thrombus) forms within the left atrium. A small piece of this clot (called an embolus) breaks off from the main clot and travels down the aorta, lodging at the end of the aorta, rapidly cutting off the blood supply to the legs. This condition is known as arterial thromboembolism (ATE) and is excruciatingly painful for the cat and needs immediate attention. The abnormal heart rhythms some cats experience can lead to fainting, or in some instances, even a sudden death.
The diagnosis of HCM is made here at Fountain City Animal Hospital via thoracic radiography (chest x-rays), EKGs, and echocardiography. Once diagnosed, we treat these cats medically, but therapy is mostly palliative, as there is no way to reduce the thickness of the heart muscle. The goals of managing cats with HCM are to improve the ability of the ventricle to fill, prevent or delay the onset of congestive heart failure, and prevent such complications as arterial thromboembolism. Despite good medical treatment, hypertrophic cardiomyopathy can progress rapidly in some cats, while in others, the condition remains relatively static for years. Many cats will have slowly progressive disease that ultimately leads to congestive heart failure or any number of other possible complications. Working together, keeping a close eye on the progression of this disease, and adding medications as necessary is the most we can do for these affected cats, knowing that each cat with HCM is unique in its disposition and environment. The ability of an owner to administer medications day after day and the tolerance a particular cat demonstrates for the process, along with the specific assessment of other concurrent medical problems a cat may have all play into how we manage each case of HCM.
Although HCM is the most common form of cardiomyopathy in cats, there are two others. The second most common type is restrictive cardiomyopathy. This condition is caused by the excessive buildup of scar tissue on the inner lining and muscle of the ventricle, which prevents the organ from relaxing completely, filling adequately, and emptying with each heartbeat.
The third type, ”dilated cardiomyopathy,” is relatively rare in cats and has many similarities to the same disease in large breed dogs. The condition is chiefly characterized by a poorly contracting dilated left ventricle. The heart walls are thin and flaccid, which results in a decreased forward flow of blood from the heart and, consequently, heart failure. The condition is rare these days due to the fact that cat food manufacturers have, for the past three decades or so, been routinely adding an important amino acid called taurine to their products. Prior to that, a lack of taurine in cat food had been closely linked to the incidence of dilated cardiomyopathy.