Cardiac Disease in Dogs
Heart (cardiac) disease is frequently diagnosed in dogs and can be a very scary diagnosis for an owner. This article will cover some of the terminology of cardiac disease and try to put the terms in everyday language so that the average pet owner can understand what the veterinarian is talking about. We will also discuss the most common types of heart problems and some of the tests used to diagnose heart disease.
Heart murmur: An abnormal sound heard when the doctor is listening to the heart beat. A normal beating heart sounds like a "Lub-Dub". A heart murmur sounds like Lub-swish-Dub, or just a Lub-Swish, or in the most severe type it sounds like Buussh. These are not really words but that is the best way to describe the sounds. We measure or grade heart murmurs on a scale of 1 to 6 and usually it is written in roman numerals (by tradition). A grade I murmur is barely audible or intermittently heard. Grade II is a little louder and consistent. Grade III is louder and consistent. Grade IV is very loud and the swish is beginning to take over the Dub. Grad V is just a loud Swish. and Grade VI can be heard without the use of a stethoscope. The murmur or sound is created by a change in the flow of blood through a valve or blood vessel which causes noise. When blood flow is altered in any way a noise is heard.
Causes of heart murmurs: Endocardiosis = Scar tissue formation on the edge of cardiac valves. This is most common cause of murmurs and is frequently the cause of murmurs heard in small breed dogs as they age. The scar tissue doesn't allow the valve to close completely. As the heart muscle contracts blood from the ventricle backs up thru the valve causing the swish sound. The two most common valves affected by this are the tricuspid valve and the mitral valve.
Endocarditis: An infection of the valve causing crumpling or scar tissue formation on the valve. This is caused by a bacterial infection. There are a few classic bacterial infections that can do this. Bordatella sp. (the causative agent for kennel cough), Bartonella sp. (transmitted by fleas) and some of the bacteria common in periodontal disease (gum disease), abscesses and some skin wounds can cause this. The 2 most common valves affected are the mitral valve and the aortic valve.
Stenosis: A birth and growth defect seen in some breeds of dogs.
Two most common types are called Aortic stenosis and Pulmonic stenosis. Both of these result in a smaller opening to a major blood vessel which acts to restrict blood flow into that vessel. The stenotic valve or vessel causes the heart to work harder though out the dog's lifetime causing the heart muscle to become stressed over time. Eventually the increased workload will cause heart failure. Many different breeds are predisposed to these conditions example are English bulldogs, Rottweilers, Boxers, Cocker spaniels, Golden retriever and many others.
Less common but occasional causes of murmurs are Ventricular septal defects = holes in the septum (middle wall of the heart), Patent ductus arteriosis = failure of a fetal blood vessel to close in young puppies.
Arrhythmia: An abnormal cardiac rhythm. The normal heart runs on an electrical current. The atrium contract then the ventricles contract. This works so that the blood moves through the blood vessels and the lungs in the correct manner. The normal workings of the heart are as follows. Blood flow comes from the body to the right atrium, the atria contract, as the ventricles relax, blood moves into the ventricles, then the ventricles contract pushing the blood into the lungs and out the aorta to the body. The contractions need to be coordinated for the blood to be at the correct velocity. When the electrical conduction is altered an arrhythmia is created and blood flow becomes altered creating a physiologic stress to the body. Blood oxygenation and blood pressure can be altered which can lead to other organs becoming malnourished or stressed. The most common cause for arrhythmia is a disease called Cardiomyopathy. There are 2 forms of this disease named by the ventricular wall thickness. Dilated cardiomyopathy is when the ventricular walls are too thin. Hypertrophic cardiomyopathy is where the ventricular walls are too thick. Whether the ventricular walls are too thick or too thin the result is the same. The muscle has been altered to the effect that the heart cannot contract correctly.
Congestive heart failure: When the heart begins to fail in its function as a pump. When the pumping action of the heart is altered enough, the blood flow throughout the body becomes altered and fluid starts to settle into body cavities and certain organs. Heart murmur disease processes and both forms of cardiomyopathy eventually lead to congestive heart failure. If the right side of the heart fails (right atrium, tricuspid valve, right ventricle) the fluid will build up in the liver, chest cavity, abdominal cavity). If the left side of the heart fails (left atrium, mitral valve, left ventricle) the fluid will build up in the lungs. When fluid builds up in body cavities or organs the dog shows signs of heart disease. These clinical signs include exercise intolerance, difficulty breathing, coughing, distended abdomen, inappetence, and occasionally fainting.
Diagnostics tests frequently performed to aid the diagnosis of cardiac disease are: Auscultation = Listening to the heart sounds and the heat rhythm. Usually done with the use of a stethoscope. A stethoscope is simply a device that amplifies the heart sounds. Thorax (chest) radiographs = Pictures of the chest cavity which will show the size and shape of the heart, and the status of the level of fluid in the chest cavity or lungs. Electrocardiogram (ECG or sometimes EKG) = A tracing of the electrical activity of the heart. This test will identify an arrhythmia (abnormal heart rhythm). Echocardiogram = An ultrasound of the cardiac muscle. An ultrasound exam of the heart will fully evaluate the architecture of the heart. The size and shape of all the valves, the thickness of the heart muscle, and the contractility of the muscle. It will also watch the blood flow (via Doppler) and any turbulence as the blood moves through each valve and vessel. Blood pressure = The measurement of the pressure in the blood vessels when the heart contracts and relaxes.
Most dogs that are suspected of having heart disease are subjected to all or most of these tests. Each test shows the veterinarian another component of the cardiac function. The more information we can collect from a patient the more educated decisions we can make on which therapies should be used to help the heart pump more effectively. Heart disease is a treatable disease. Many dogs can live for months to years depending on the severity of the underlying disease process. There are many different drugs used to treat each component of the cardiac disease. Each dog is different and some dogs will require a few drugs to control each component of the disease process.
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Dr. Ellen Leonhardt
Animal General
East Norwich
(516) 624-7500
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