First, it needs to be known that HCM can and does affect *all* breeds of cat. Whether a domestic or purebred, the disease has been found. HCM is also a human disease. Familial hypertrophic cardiomyopathy (HCM) in humans is caused by mutations in genes encoding for sarcomeric proteins. It has been discovered that hypertrophic cardiomyopathy is inherited as an autosomal dominant trait in Maine coon cats and that the disease has all of the other characteristics of familial HCM in humans. In cats, there is a 50% chance of the offspring of an HCM postive parent, to inherite the gene for HCM (the same applies to humans).
What is HCM?
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 volume of blood to supply the demands of the body.
Hypertrophic Caridomyopathy is the most common form of acquired heart disease in the cat. This condition is often called a silent killer because many cats show no outward signs of HCM before it is very advanced or until their heart rate is elevated due to stress, pain, drugs etc.. Clues that HCM may be present include, but are not limited to; nonspecific signs of illness such as poor appetite, depression, inactivity or reluctance to move. Difficult and/or rapid breathing may be noticed, however a cough is very unusual. Some cats present with hind limb paralysis and severe pain due to thromboemboli.
In most cases clues to this condition are detected during routine physical examinations. The sad thing is many owners decline the further investigation that is required to definitively determine the presence of HCM. Auscultation of the chest (listening to the heart with a stethoscope) often reveals a heart murmur. A murmur is an abnormal heart sound caused by turbulent blood flow. The loudness or tone of a murmur is not directly proportional to the seriousness of the underlying abnormality. Often very quiet murmurs are caused by very serious heart problems.Arrythmias, abnormal heartbeat sequences, such as gallop rhythms, may be detected. In cats with HCM the heart rate is often faster than normal. In many cases the murmur and/or gallop rhythm is only detected when the cat is stressed and the heart rate is fast. Thus, when the stethoscope is first applied to the chest wall and the cat is anxious these changes may be detected only to disappear as the cat relaxes and the heart rate lowers. This does not mean that the cat is normal after all. On the contrary..it can be the first clue to detecting a lethal heart condition and should not be underestimated!
Cases that present as emergencies often exhibit open mouth breathing and sternal recumbency. The mucous membranes may be blue due to poor oxygenation. As mentioned previously some present with painful hindlimb paralysis.
If your cat has a murmur of any loudness or a gallop rhythm, even if transient, it warrants further investigation. Chest radiographs showing the cardiac silhouette and an ECG can be indicative of HCM. However, cardiac ultrasonography (echocardiography) is the diagnostic tool of choice in confirming and categorizing HCM.
There are other conditions can result in thickening of the left ventricular wall. Hyperthyroidism and systemic hypertension should be ruled out as possible underlying causes. In cats with diabetes Acromegaly should be considered. In young cats, or those with long standing cardiac murmurs, the underlying cause could be congenital aortic stenosis or mitral valve dysplasia.
In order to effectively treat heart disease it is imperative that it is properly diagnosed and any underlying conditions be determined and addressed.
Diagnosis in early stages can be tricky, some of the symptoms are as follows: lethargy, poor appetite, labored and panting/troubled breathing. Often, a feline will develop a heart murmur along with HCM. Also, possible lameness or paralysis of the hind legs due to arterial blood clots. Cardiomyopathies can cause congestive heart failure, cardiac arrythmias, sudden death and systemic arterial embolism (saddle thrombus). Some cats will show no symptoms at all, appearing perfectly healthy to the owner, yet quickly succumb to the disease with no warning.
The best form of diagnosis is via a dopler echocardiogram (an noninvasive test that uses ultrasound (sound waves) to evaluate the structures, function, and blood flow of the heart). If the cat is in the early stages of HCM, the echcardiogram will usually show thickening of the left ventricular wall, papillary muscles, and septum.
Males and females should be tested around one year of age (this is generally when the early onset of the disease is present). It seems that males will often show the disease at a younger age than the female. Some females may not show evidence of the disease until they are 3-5 years of age. This is why males and females in a breeding program should be tested every 1-2 years.
Prognosis is fair if arrhythmias and clots can be controlled medically. Unfortunately, diagnosis often comes to late, and in advanced stages of the disease. Early detection and treatment/control lends to a more favorable prognosis. Even in more advanced cases with a history of pulmonary edema or a resolved thromboembolism, some cats, on appropriate medication, will live two years or more. However, in all cases this condition is serious and life threatening.
Treatment is through medication to both thin the blood and to reduce the workload on the heart and improving oxygenation of the blood. Several types of vet-prescribed medications can be administered: atenolol (generic for tenorim, a beta blocker, which lowers blood pressure), lasix or other diuretics, Cardizem and Verapamil (an antidysrhythmic and antianginal agent).