Murmurs of the Heart

The prognosis depends on the underlying cause and at which stage the signs are recognized.

A heart murmur is the sound of turbulent blood flow, signaling anything from a minor abnormality in the hearts structure to a serious disease. While its not a disease in itself, veterinarians do consider it a red flag.

Before an owner makes any decisions on treatment, you need to find out why the murmur is there, explains Marc Kraus, DVM, faculty member at the Cornell University College of Veterinary Medicine and service chief of the cardiology section at Cornell University Hospital for Animals. Its like saying you have a toothache; if you dont know the cause, how do you know what to do about it?

A murmur is usually detected with a stethoscope, but a proper diagnosis requires a full physical exam, chest X-rays, electrocardiogram (EKG, which charts the electrical activity of the heart) and echocardiogram (ultrasound of the heart). Veterinarians generally perform preliminary diagnostics to rule out other diseases, but may refer patients to a cardiologist if heart disease is suspected.

Crucial Elements of Diagnosis
The age and history of the cat – and the results of tests for non-cardiac diseases – are crucial to an accurate diagnosis and individualized treatment. If you have a 10-week-old kitten with a very soft murmur (heard during part of the heart beat cycle called systole), you could re-evaluate at four-months-old and see if it has gone away, says Dr. Kraus, adding that a kittens heart physically changes as it grows. Or if your cat is 10-years-old, youd want to look for hyperthyroidism or kidney disease that creates a murmur, without the heart being at fault. 

An increase in the speed of blood flowing through the heart causes the murmur, and may not be related to actual heart disease. For example, functional murmurs can result from a higher velocity flow due to exercise, fever or hyperthyroidism. Anemia, which thins the blood so it moves faster, can be caused by flea bites or kidney disease. Hypertension enlarges the aorta, changing the diameter of the blood vessel.

Heart murmurs can be congenital (from birth) or acquired (will develop later). Congenital murmurs are usually due to malformations of the heart, but acquired murmurs can be caused by various diseases, parasites, infection, weakened valves or altered heart muscles. They can also be caused by temporary conditions like stress or excitement.

The Most Common Cause
Still, heart diseases and abnormalities – especially leaky valves, small holes, and thickening of the heart muscle – remain the most common reason for murmurs. In cats, one of the most common cardiac diseases is cardiomyopathy, and when we hear a heart murmur, we look for that, Dr. Kraus says.

There are three types of feline cardiomyopathy, but hypertrophic cardiomyopathy (HCM) is the most common, wherein the left side of the heart thickens and bulges. Domestic short hairs, Ragdolls, Maine Coons and Persians seem prone to this genetically-linked disease.

However, cardiomyopathies dont always cause an audible murmur. Especially in dilated cardiomyopathy (a less common form of the disease in which the heart muscle becomes abnormally thinned), you may not hear a murmur at all, says Dr. Kraus. Our ears just cant pick up the sound of mild abnormalities – but an echocardiogram would.

Useful Tool: Echocardiogram
Importantly, echocardiograms also can distinguish between types of cardiomyopathies. Since the cat heart is very small – about the size of an egg – it may be difficult to determine the exact location of the murmur with a stethoscope, Dr. Kraus continues.

Also, cats that are stressed by a veterinary exam can have an inordinately rapid heartbeat, making a simple diagnosis impossible. Is the murmur on the right side of the heart, the left side, the sternum? Dr. Kraus asks.

Consequently, an echocardiogram and possibly an EKG are needed to pinpoint where the heart problem is and to determine the prognosis. Ultimately, cats with heart murmurs can get better or worse or stay the same.

Some murmurs are correctable, Dr. Kraus explains. Some cats have a congenital continuous murmur, which is surgically repairable. If animals have a curable disease (such as hypertension, controlled with drugs) the heart changes may be reversible. On the other hand, some diseases (such as hyperthyroidism) can cause permanent heart damage if they go untreated too long.

The prognosis depends on the underlying disease and how fast we intervene, he concludes.