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Cardiomyopathies: When hearts get broken, part 2
This is the second of a two-part series on cardiomyopathies.
The first article in this two-part series focused not only on the definition of a cardiomyopathy, but also some basic anatomy and physiology of a healthy heart. This article will focus on the two most common types of cardiomyopathies in dogs and cats.
Dilatory cardiomyopathy is the most common form of cardiomyopathy in dogs. Dilatory cardiomyopathy refers to a thinning of the heart muscle and secondary dilation of the heart itself.
Initially, we worry about the dilated heart as an ineffective pump. This leads to a fluid backup into the lungs or abdominal cavity (congestive heart failure). Unfortunately, dilatory cardiomyopathy also affects the electrical system of the heart and leads to arrhythmias. Arrhythmias are irregular or abnormal heart rhythms. Arrhythmias not only prevent the heart from filling and ejecting blood effectively, but also put a strain on the heart muscle that could lead to asystole.
Asystole is derived from the Greek words "a", which means "without", and "systole", which means "contraction." Therefore, asystole is when the heart stops beating completely (flatline). The chances of reviving a pet from flatline (even under the best circumstances) are very small.
Many times these arrhythmias will lead to terminal asystole as a first sign of disease (sudden death from cardiac arrest). Therefore, diagnosing any pathology associated with the heart muscle is important to pick up as early as possible. Breeds that are more at risk for dilatory cardiomyopathy include Doberman pinschers, boxers, great Danes, St. Bernards, and Newfoundlands (just to name a few).
Hypertrophic cardiomyopathy is a disease of the heart which is much more common in cats. Unlike dilatory cardiomyopathy, hypertrophic cardiomyopathy causes the heart muscle to become thickened and less pliable. This not only reduces the heart's ability to pump effectively, but also changes the shape of the chambers. A change in shape of the chambers of the heart leads to swirling or turbulence of the blood as it passes through.
Blood is not only made up of fluid and red blood cells (to carry oxygen), but also white blood cells (to fight infection) and platelets (to help form clots). If the platelets rupture secondarily to turbulence within one of the chambers, clots will form. If these clots are big enough, portions of them (or entire clots) can break off and travel out of the heart clogging arteries to vital organs.
In people, clots many times develop in the carotid artery, and if they break off go to the brain (stroke). In cats, these clots usually develop in the left ventricle and when they break off they travel down the aorta away from the brain. These clots continue down the aorta until it bifurcates, or divides into the two major arteries supplying the back legs. A blood clot there is extraordinarily painful because without blood to the back legs, the muscles will begin to cramp violently. If the clot is not either broken down (by the body or with medication) or surgically removed (this is a very risky procedure), the patient will become either partially or completely paralyzed in the back legs.
Two breeds that are more at risk for hypertrophic cardiomyopathy include the Maine coon and Ragdoll breeds. Unfortunately, any mixed breed cat can also develop this condition, so having your basic "Heinz 57" model does not preclude a genetic predisposition for this.
Definitive testing for both types of cardiomyopathies include an electrocardiogram (EKG), echocardiogram (ultrasound of the heart), X-rays of the chest, and blood work (to evaluate internal organ function and rule out other concurrent disease). These noninvasive tests not only diagnose this disease, but also help to stage it. Staging cardiomyopathies provides the information necessary to not only choose the appropriate medication, but also give the pet's owner an idea of how quickly the disease will
So, if your veterinarian hears a murmur or irregular heart rhythm this is not a diagnosis of disease, but rather abnormality. Let them prescribe the appropriate testing to figure out what is wrong. It could save your pet's life (literally).
Dr. Kearns has been in practice for 12 years and is pictured with his son Matthew, as well as the newest member of the family, Jasmine, a Labrador retriever.