All cats face the risk of heart disease, from domestic shorthairs to prized rare breeds, but the signs can remain undetected for years before resulting in diminished or total loss of cardiac function. The challenge for owners is to be alert to subtle changes in their cats.
“Open-mouthed and/or rapid breathing, lethargy, weakness, unkempt appearance, anorexia and weight loss are all potential indicators of heart disease,” says cardiologist Bruce Kornreich, DVM, Ph.D., ACVIM, Associate Director of the Feline Health Center at Cornell University College of Veterinary Medicine. “Although these signs may be caused by other conditions, owners should contact the cat’s veterinarian immediately if any of them are observed.”
Given that cats often reduce their activity level when ill, it may be difficult to determine if their breathing is labored. The best time is to check is when they’re at rest or sleeping. (See sidebar on Page 6.)
By far the most common heart disease in cats is hypertrophic cardiomyopathy (HCM), which can be life threatening to both cats and humans. “It affects up to 2 percent of all cats over a broad age range,” Dr. Kornreich says. “The condition is characterized by thickening of the walls of the heart’s left ventricle and affects the heart’s ability to pump oxygenated blood to the body.”
The ventricles are the two lower, muscular heart chambers that provide most of the energy to pump blood. Hyperthyroidism and high blood pressure can also cause thickened ventricles, so it’s important to rule these out before arriving at a diagnosis of HCM. Whatever the cause of the thickening, “A stiffened chamber usually cannot relax appropriately between contractions, which affects the ability of the ventricle to fill between contractions, decreasing the amount of blood ejected per contraction” says Dr. Kornreich.
“This raises the heart rate because the heart needs to beat more times to maintain a normal cardiac output. This rapid heart rate leads to increased oxygen consumption by the heart muscle, which can result in the death of heart cells and worsening cardiac function.”
HCM is often accompanied by fluid accumulation either in the lungs or the pleural space, which is within the chest cavity and surrounds the lungs.
Some breeds are more predisposed to HCM than others. “It is an inherited condition in Maine Coon, American Shorthair and Ragdoll cats,” Dr. Kornreich says. “HCM is likely the result of a genetic mutation or series of mutations, although how these mutations cause the thickening of the ventricle walls is still unknown.”
These mutations serve as the basis of screening tests for hypertrophic cardiomyopathy, although the results of these tests must be interpreted carefully. Despite this limitation, genetic screening may be helpful in refining breeding programs to minimize the incidence of HCM in cats, Dr. Kornreich says.
The first step toward diagnosis is to share your cat’s history with a veterinarian. He or she will want to know whether your cat has had other diseases that may produce similar symptoms, including asthma, cancer or heartworm disease. Chest radiographs (X-rays) can reveal diseases such as asthma, cancer or pneumonia that the owner might not be aware of. Radiographs might also show an enlarged heart, along with evidence of fluid accumulation, such as enlarged vessels, fluid filled lungs or fluid in the pleural space.
A very important test in the diagnosis of heart disease is echocardiography, which provides vital information about the structure and function of the heart. “This is the gold standard for the diagnosis of HCM,” Dr. Kornreich says.
Upon examination, cats with heart disease may have an arrhythmia or a heart murmur. “The heart is caused to pump by a very specific series of electrical impulses,” Dr. Kornreich says. “An arrhythmia refers to any change from the normal rate and sequence of electrical impulses. The impulses may happen too rapidly, too slowly or erratically. This causes the heart to beat abnormally, and when the heart doesn’t beat properly, it can’t pump blood effectively. Then the lungs, brain and other organs may be deprived of sufficient amounts of oxygenated blood and may shut down or be damaged.”
The causes of arrhythmia are many and varied. “We know relatively little about the cat’s genetic predisposition to arrhythmia,” Dr. Kornreich says. “In cats, arrhythmias are commonly seen secondary to other diseases such as hypertrophic cardiomyopathy.”
Cats with arrhythmias may need a 24-hour electrocardiogram, obtained via a device called a Holter monitor, to characterize their frequency and severity.
Nearly 20 percent of all normal adult cats have a heart murmur, which results from turbulent flow of blood through the heart. “A murmur is not a diagnosis in itself, although it may prompt a veterinarian to recommend additional diagnostic tests, including echocardiography and thoracic radiographs (X-rays),” Dr. Kornreich says.
Cats in congestive heart failure who demonstrate respiratory distress usually require drug therapy to decrease congestion and will often benefit from being placed in an oxygen-enriched environment. They may also be prescribed medications to decrease the likelihood of blood clot formation, a potentially devastating consequence of heart disease in cats.