Contents
What does cardiomyopathy mean?
The various forms of cardiomyopathy.
Heart Murmurs & cardiomyopathy.
The Electrocardiogram & cardiomyopathy.
The Radiographs & cardiomyopathy.
The Echocardiogram & cardiomyopathy.

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What does cardiomyopathy mean?

Derivation and Definitions: cardio- = heart; myo- = muscle; pathos- = disease

Cardiomyopathy is a term that is used to describe diseases of the heart muscle. There are many types of heart disease, but cats generally develop three different forms of heart muscle disease: dilated cardiomyopathy, restrictive cardiomyopathy, and hypertrophic cardiomyopathy. Each of these conditions is different, but ultimately they cause problems because the heart becomes unable to pump an adequate amount of blood to supply the body. Just like humans, cats can have heart disease for a long time before developing heart failure. A severe, life-threatening condition, heart failure occurs when the heart is no longer able to pump enough blood to supply the tissues with the oxygen they require. The right side, left side, or both sides of the heart can fail, causing a number of complications.

One of the most severe forms of heart failure occurs when the lungs fill with fluid, a condition called pulmonary edema. This complication occurs because the left side of the heart is not pumping blood effectively. Excessive pressure builds up behind the pump, and fluid leaks into the air spaces in the lungs. Thus, the cat effectively is drowning in its own fluids, which inhibits the exchange of oxygen between the lungs and the blood. The result is that the cells of the body do not receive enough oxygen and begin to die. If uncorrected, pulmonary edema leads to multiple organ failure and death.

Another complication of heart disease in cats is the development of a blood clot, clinically known as aortic thromboembolism, which usually forms in the heart and travels through the blood stream. Most commonly, the clot lodges at the branch of the aorta that feeds the back legs, shutting down blood flow and causing partial or complete paralysis. This condition is excruciatingly painful and requires immediate medical attention. Cats experiencing an aortic thromboembolism will be unable to move their back legs and may vocalize due to the pain. Aortic thromboembolism usually indicates significant heart disease; two thirds of cats that develop this condition will die or be put to death humanely. In cats that survive aortic thromboembolism, recurrence is common.
 
Common clinical signs include tachypnea, panting associated with any activity, dyspnea, coughing, anorexia, vomiting, weight loss and lethargy. Some cats will develop hind leg paralysis, loss of femoral pulses, and cool limbs due to thromboembolism. Syncope or sudden death may also occur. Often, a heart murmur, gallop rhythm, or abnormal lung sounds are detected on auscultation of the heart. The cat may have experienced recent stresses such as anesthesia, surgery, boarding, or car rides that caused it to develop heart failure.


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The various forms of cardiomyopathy:

A primary (idiopathic) cardiomyopathy is a disease of heart muscle with no known underlying etiology. Primary Cardiomyopathies are diagnosed by the morphologic and functional appearance of the patient’s heart and ruling out other causes for these “patterns”.

     











                Normal heart                                   HCM heart



  - Hypertrophic cardiomyopathy (HCM): concentric (symmetric or asymmetric)
    hypertrophy.
        Hypertrophic cardiomyopathy, the most common form of feline heart muscle disease, occurs
        when the lower left chamber of the heart, called the left ventricle, thickens and stiffens, while
        the top left chamber, the left atrium, enlarges. This thickened left ventricle does not leave much
        room in the chamber to fill with blood. Thus, smaller than normal amounts of blood are
        pumped out of the heart with each contraction. Additionally, this thickening of the heart muscle
        increases the heart's own consumption of oxygen, which is needed to supply the additional
        muscle present. If these oxygen demands are not met, then cell death occurs and leads to
        areas of scarring in the heart muscle.


 











                Normal heart                                    DCM heart



- Idiopathic Dilated cardiomyopathy (DCM): eccentric hypertrophy with
  myocardial failure.
        Dilated cardiomyopathy, occurs when the heart chambers become big and dilated, like a
        "flabby balloon." With dilation, the heart muscle is often weakened dramatically so that it
        cannot contract with the normal amount of force. This disease was very common before it
        was recognized that the majority of cases were due to a dietary deficiency of the amino acid
        taurine. Since commercial diets now adequately are supplemented with taurine, this disease
        is uncommon.

 - Restrictive cardiomyopathy (RCM).
        Restrictive cardiomyopathy has also been called intermediate cardiomyopathy because it has
        characteristics of both dilated and hypertrophic cardiomyopathy. With this form of the illness,
        the walls of the cat's heart develop fibrosis, which is the replacement of normal heart tissue
        with scar tissue that does not function as well. This scarring makes the heart stiff and less
        effective as a pump.

A secondary cardiomyopathy is a heart muscle disease resulting from other disease processes. Proven or strongly suspected causes of Secondary Cardiomyopathy in Cats:
    - Nutritional (taurine deficiency).
    - Metabolic (hyperthyroidism, acromegaly).
    - Infiltrative (neoplasia, amyloidosis).
    - Inflammatory (toxins, immune reactions, infectious agents).
    - Genetic (strong evidence in HCM in some breeds; may play a role in
       the susceptibility to taurine deficiency induced myocardial failure).
    - Toxic (doxorubicin, heavy metals).

Within each class, wide ranges of morphologic and clinical presentations are seen. The lines between forms and classifications begin to blur as the facts are unraveled.


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Heart Murmurs and cardiomyopathy:
At the very least, breeding cats should be examined by a vet with a stethoscope for heart murmurs or arrhythmias once yearly. Any cat with an abnormality should have an echocardiogram. A significant percentage of cats with HCM will not have a heart murmur, however.

    Grade 1
        A very soft murmur only detected after very careful auscultation
    Grade 2
        A soft murmur that is readily evident
    Grade 3
        A moderately intense murmur not associated with a palpable precordial thrill (vibration)
    Grade 4
        loud murmur; a palpable precordial thrill is not present or is intermittent
    Grade 5
        A loud cardiac murmur associated with a palpable precordial thrill; the murmur is not audible
        when the stethoscope is lifted from the thoracic body wall
    Grade 6
        A loud cardiac murmur associated with a palpable precordial thrill and audible even when the
        stethoscope is lifted from the thoracic wall


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The Electrocardiogram:
Indications for electrocardiography include arrhythmias heard on auscultation, breathing problems, shock, fainting or seizures, cardiac murmurs, and systemic disease that affects the heart (e.g. tumors, kidney dysfunction, heartworm disease). Electrocardiography is also useful as part of the preoperative work-up in older animals, for monitoring patients during and after surgery, and for evaluating the effects of cardiac drugs. An electrocardiogram (ECG) is the only test that can accurately diagnose an arrhythmia or a conduction abnormality. And an ECG will help you decide when other diagnostic tests should be done, including, thoracic radiography, or even echocardiography.


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Click on the box to the left for a link to the article.
The article show both x-rays and echocardiograms.



The Radiographs:
Chest radiographs (x-rays) of asymptomatic cats may appear normal or may show mild enlargement of the heart. In cats with clinical signs of HCM there may be greater enlargement of the heart as well as evidence of fluid buildup in the lungs and chest cavity.


The Echocardiogram:
This is the most important diagnostic tool the vets have for HCM. An echocardiogram is a test in which ultrasound is used to examine the heart.  In
addition to providing single-dimension images, known as M-mode echo that allows accurate measurement of the heart chambers, the echocardiogram also offers far more sophisticated and advanced imaging. This is known as two- dimensional (2-D) Echo and is capable of displaying a cross-sectional "slice" of the beating heart,
including the chambers, valves and the major blood vessels that exit from the left and right ventricle. Doppler is a special part of the ultrasound examination that assess blood flow (direction and velocity). In contrast, the M-mode and 2-D Echo evaluates the size, thickness and movement of heart structures (chambers, valves, etc.). During the Doppler examination, the ultrasound beams will evaluate the flow of blood as it makes it way though and out of the heart. This information is presented visually on the monitor (as color images or grayscale tracings) and also
as a series of audible signals with a swishing or pulsating sound.


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