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Don’t Go Breaking My Heart – Understanding Heart Disease in Cats and Dogs

With Valentine’s Day just around the corner, it’s hard not to think about hearts. Heart disease is a major health concern in human health care, but many people don’t know that heart disease can be a problem for our pets, too.

A Dynamic, Complicated Organ 

The heart is a complex organ, with lots of moving parts that work together in a precise and orderly way to pump blood throughout the body. Over time, heart function can be compromised by a multitude of factors, including illness, genetics and other stresses. The heart can compensate to a point but eventually function will decline, leading to signs of heart failure.

A useful way to think about heart disease is to consider the different parts and functions of the heart. Understanding how the heart works when healthy can help us understand more about the diseases that can affect our pets.

The heart is a specialized muscle, designed to fill with blood then contract, ejecting blood to begin its journey to all parts of the body. Inside the heart, valves help direct blood flow in the proper direction. An electrical system provides the signals to direct the heart muscle to contract in a regular and orderly fashion. And thousands of blood vessels, from the large and powerful aorta to the tiniest capillaries, serve as the conduits for blood as it travels throughout the body. 

A disruption to any part of this complex pathway can change the functional capacity of the heart. Let’s start by looking at diseases of the heart muscle, and then move to diseases affecting the other main parts of the heart: valves, blood vessels and the electrical conduction system.

Cardiomyopathy – Disease of the Heart Muscle

Cardiomyopathy is the general term applied to diseases affecting the heart muscle, and it can take several forms. For example, dilated cardiomyopathy is type of heart disease characterized by a thinning of the heart muscle, decreasing the heart’s ability to contract. In contrast, hypertrophic cardiomyopathy is a disease characterized by thickening of the heart walls. Although initially the heart is able to contract normally, as the muscle thickens, the heart is less able to contract. Less blood enters the heart, so output decreases. Eventually, the heart muscle also fails. There are lots of intermediary and combinations of heart muscle disease, but all forms begin as abnormalities of the muscular structures of the heart.

Dilated Cardiomyopathy and Hypertrophic Cardiomyopathy

Dilated cardiomyopathy is most commonly seen in large breed dogs, especially in certain breeds such as Doberman pinschers, Great Danes and Irish wolfhounds, although many breeds are known to develop the disease. The disease tends to affect middle-aged to older dogs but is treatable if caught early. Less commonly, dilated cardiomyopathy can be the result of certain chemotherapy drugs and nutritional abnormalities. The disease is treatable and prognosis is better if caught early. 

Hypertrophic cardiomyopathy is not only the most common type of heart muscle problem diagnosed in cats, it is the most common heart disease of cats. Cats with HCM also are prone to abnormal blood clots, which can form and block major blood vessels. 

There is a genetic component implicated in some cat breeds (for example Maine coon cats) but many mixed breed cats also suffer from this problem. Once again, early diagnosis is the key to successful treatment and longer, healthier lives for cats living with this condition.

Arterial Thromboembolism in Cats

The formation of large, abnormal blood clots, known as arterial thromboembolism, is a common problem in cats with cardiomyopathy. 

The most common place for a large clot to lodge is in the distal aorta as it splits into the main vessels that supply each leg. Commonly referred to as a saddle thrombus, this results in a loss of blood flow to both rear legs, leading to pain and loss of movement in the rear legs. 

Other organs also can be affected by abnormal blood clots, such as the kidney and brain. Although treatable, prevention of clot formation through specific treatment and treatment of the underlying heart problem is critical.

Heart Valve Abnormality 

Heart valve problems are another type of heart disease that affects cats and dogs. There are four valves in the heart, two on the right side of the heart (the pulmonic and tricuspid valves), and two on the left (the aortic and the mitral valves). Diseases affecting the valves result in abnormal blood flow in the heart (valve disease is a common cause of murmurs), which places strain on the heart as it tries to compensate for abnormal flow through thickening of the muscles and dilation of the chambers. Once again, eventually the heart can no longer compensate and begins to fail.

Degeneration of the Mitral Valve in Dogs

Myxomatous degeneration of the mitral valve (MMVD) accounts for nearly 75 percent of all heart problems seen by veterinarians, making it the most common heart disease diagnosed in dogs. Affecting mostly middle-aged to older small breed dogs, the disease is a common cause of heart murmurs detected in dogs. 

The mitral valve separates the left atrium and the left ventricle. As the valve degenerates, blood can flow backwards through the valve, resulting in volume overload on the heart, and a decrease in blood flow out of the heart into the body. MMVD is treatable when identified early, and many dogs with the diseases have an excellent quality of life.

Subvalvularaortic stenosis is the most common congenital heart defect in dogs. The disease is a bit of a combination between a muscular problem and a valve problem. Thickening of the tissue just below the aortic valve causes a narrowing of the outlet between the muscular left ventricle and the aorta, the main artery leading blood away from the heart. The disease is often hard to detect, and many dogs have no signs of heart disease. Unfortunately, the disease can cause sudden death in severely affected dogs. Breeds predisposed to this defect include Newfoundlands, golden retrievers, Rottweilers and boxers, although it has been reported in many other breeds. Genetic testing is available as a screening tool. 

Interestingly, cats rarely develop primary heart valve problems although the valves can be affected by other heart diseases.

Irregular Heartbeats

The heart’s rhythm is also an important component of adequate function. If we think of the heart as having an electrical system that sends signals to coordinate heart muscle contraction and relaxation, any short circuit in the system can lead to an irregular heartbeat, and then decreased function. When the heart begins to beat irregularly (arrhythmia), the heart may not fill properly with blood and not eject blood consistently or completely. Different areas of the heart can start generating their own electrical activity, compounding the problem; once again, compensatory mechanisms will eventually fail.

Many arrhythmias in our pets are secondary to other abnormalities, such as electrolyte abnormalities, hyperthyroidism in cats, and shock or trauma, and others are secondary to underlying heart disease, such as dilated cardiomyopathy. Treating the underlying problems often resolves an irregular heartbeat, but occasionally medication is needed specifically aimed at correcting the abnormal heart beats.

Coronary Artery Disease

Finally, a quick word about coronary heart disease. Dogs and cats rarely get coronary artery disease, which is a huge problem in people: the classic heart attack. Although myocardial infarctions (blockages of the coronary arteries) have been reported in the veterinary medical literature, they are very rare. 

Regular Health Check-ups Can Catch Heart Problems Early

Routine veterinary visits can help detect emerging heart problems, and owners can watch for common signs of heart disease such as fatigue, decreased appetite and increased respiratory rate and effort. Many heart diseases are treatable, but only when caught early and treated appropriately.

Morris Animal Foundation has been funding heart disease studies in dogs and cats since 1960. Our studies have covered cardiac issues from understanding canine ECGs to our most recent studies looking at the genetic basis of heart disease in dogs and cats. Our funding has helped determine the best treatment for cats with arterial thromboembolism, test a cutting edge treatment for irregular heart rhythms in dogs, and develop ground breaking genetic screen tests for congenital heart disease in both dogs and cats. We’re passionate about helping dogs and cats live longer, healthier lives.

Categories: Cat health, Animal welfare, Animal health, Canine health
February 8, 2018