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CARDIOLOGY: HYPERTROPHIC CARDIOMYOPATHY IN CATS

YVCipedia CARDIOLOGY
HYPERTROPHIC CARDIOMYOPATHY IN CATS

  • Heart disease is not the same thing as heart failure. A cat can have a diseased heart that functions normally. Heart failure occurs when the abnormal heart can no longer function normally. 
  • Some, but not all cats with heart disease develop heart failure. Some cats with heart disease develop complications other than heart failure, including arrhythmias (abnormal beat patterns) and formation of blood clots (thrombosis) that lodge in blood vessels outside of the heart. Some cats with heart disease never have significant complications from their problem. 
  • There are different types of heart disease in cats; by far, the most common is cardiomyopathy (CM), which is disease of the heart muscle. 
  • There are different types of CM.
  • With few exceptions, CM is a progressive, incurable problem. The rate of progression is unpredictable. 
  • The most common type of CM in cats is hypertrophic cardiomyopathy (HCM). HCM is characterized by abnormal enlargement of the heart muscle. 
  • HCM is a very common problem. The best current estimates from veterinary research are that 15% to 30% of all cats have HCM. 
  • There are several different possible causes for HCM; most cases are of unknown and undetectable cause.
  • Several breeds of cats have an inherited tendency towards HCM. Maine Coon Cats, Ragdolls, and Persians are the most common breeds with this tendency; other predisposed breeds include British Shorthair, American Shorthair, Norwegian Forest, Turkish Van, Sphynx, Bengal, and Scottish Fold. 

SYMPTOMS OF HYPERTROPHIC CARDIOMYOPATHY

  • Most cats with HCM seen at YVC have no symptoms; their problem is detected during a routine physical exam, or an exam for an unrelated health problem.
  • When signs of illness due HCM are present most often they include one or more of difficulty breathing, rapid breathing, weight loss, weakness, lethargy, loss of appetite, or sudden, painful paralysis of one or more limbs.
  • Less common symptoms are fainting, collapse from weakness, coughing, or a large, round abdomen. 
  • Symptoms usually appear quickly, with few or no prior signs of illness, but they can appear gradually. 

DIAGNOSIS: FOR CATS WITH SYMPTOMS

  • When we are presented with a cat that has symptoms because of HCM, we can usually get enough information from our physical exam and the pets history to be somewhat certain this is the problem. Definitive diagnosis requires an echocardiogram.
  • An echocardiogram is an ultrasound exam of the heart. It is not painful, and non-invasive. A very small percentage of the cats that we see for echocardiography are anxious enough that we will use a sedative or general anesthesia, but the majority of our patients do not need either. Echocardiography is a test that we routinely perform at Yarmouth Vet Center. 
  • Cats that are sick with HCM also need other tests, for a few reasons: to determine if their symptoms are due to HCM or some other problem; to determine, if possible, the cause of the HCM; to determine the extent of the problems associated with HCM; and to establish the pets overall health status. This, in turn, tells us what the most useful treatments are, and gives us the ability to give the owner the most accurate prognosis possible. 
  • The tests that we routinely use in addition to an echocardiogram are x-rays, blood tests, and blood pressure measurement.

DIAGNOSIS: FOR CATS WITH NO SYMPTOMS DUE TO HCM

  • As mentioned previously, most of the cats that we ultimately diagnose with HCM present to us with no symptoms.
  • We usually see these cats for an annual exam, or an exam for a problem unrelated to HCM. During this exam we discover a heart murmur. 
  • There are many possible reasons for a heart murmur other than HCM. In some cases the murmur is “innocent”; that is, the cat does not have a health problem.
  • On the other hand, HCM is a very common problem: depending on the research criteria used, 18% to 62% of symptom-free cats with a heart murmur have HCM as the cause. As a result, when we hear a heart murmur during the physical exam of a cat that appears healthy, we have a relatively high level of suspicion that the pet has HCM.
  • At YVC, we believe, for many reasons, that there is great value in performing an echocardiogram on symptom-free cats that have a heart murmur. One very important, practical reason is that an accurate diagnosis of the cause of the murmur allows us to medically intervene earlier in the course of the pets problem, at a time when treatment and preventive care is much more likely to be effective.
  • We do not medically treat symptom-free cats that we diagnose with a heart murmur when we do not have at least an echocardiogram to confirm the reason for the murmur. There are reasons other than HCM for a murmur, and the treatments we use are specific for the specific problems. There are substantial risks with using the wrong treatment for a problem, especially when those treatments are heart medications.

DIAGNOSIS: THE SLEEPING RESPIRATORY RATE 

  • The sleeping respiratory rate (SRR) is a very sensitive test for heart failure. 
  • It is also a sensitive test for monitoring the response to medical treatment for heart failure. 
  • It is very easy to monitor SRR at home. Please ask us for our article on this topic, or find it on our website:  https://yarmouthvetcentercom.vetmatrixbase.com/yvcipedia--cats---dogs--birds--reptiles--rabbits--rodents-and-other-small-mammals--ferrets--fish/cats-and-dogs/sleeping-respiratory-rate.html

TREATMENT AND PROGNOSIS: FOR CATS WITH NO SYMPTOMS OF HCM

  • There is a lack of research on the impact of medical management on the progression of illness in symptom-free cats with HCM. In other words, we do not have much research evidence for or against using medication to slow the progress of HCM, and/or improve the pets quality of life.
  • There are typically two medications, one given once daily to reduce the risk of clot formation, and the other given twice daily to “lower the workload” of the heart, that we use for medical management. They are inexpensive, small pieces of small tablets. Side effects from either medication are extremely unlikely. Both medications are lifelong. Occasional missed doses are very unlikely to cause a problem. 
  • If, on a mild / moderate / severe scale, an echocardiogram shows that a cat is severely affected with HCM then our recommendation is to start medication.
  • If an echocardiogram shows  the cat is mildly or moderately affected, then we usually have two other considerations: First, some cat owners do not want to use medication unless there is overwhelming evidence to do so. For these owners our recommendation is to not medicate, and to monitor for progression of the disease (see below). 
  • Second, some cats are easier to medicate than others, and attempting to give daily medication to a difficult-to-treat cat will, sooner or later, ruin the owner’s relationship with their pet. If the cat is relatively easy to medicate then we recommend doing so, if it is difficult to medicate then we recommend monitoring only (see below.)
  • HCM is a progressive disease: the heart abnormalities get worse with time, and the pets risk of developing heart failure, clot formation, or some other complication increases. We recommend monitoring our patients with regular recheck physical exams and echocardiograms. We decide the relative frequency of these tests on a pet-by-pet basis; usually the rechecks are every 6 to 12 months. 

TREATMENT AND PROGNOSIS: FOR CATS WITH HEART FAILURE DUE TO HCM

  • Heart failure as a result of HCM can be mild, moderate, or severe. 
  • Treatment of severe heart failure begins with intensive care. Not every cat with severe heart failure will survive. Intensive care usually has to continue for 2 to 3 days for the patient to be stabilized, or for us to learn that they cannot be stabilized. 
  • In addition to medications, treatment of severe heart failure usually involves oxygen therapy and often involves needle aspiration of abnormal fluid from the chest (thoracocentesis). 
  • Treatment of mild to moderate heart failure can usually begin on an outpatient basis with prescribed medications. 
  • Periodic recheck examinations and echocardiograms are a necessary part of management of heart failure. At YVC, the frequency of these rechecks is determined on a patient-by-patient basis. 
  • In one large study, survival time for cats in heart failure due to HCM was an average of 563 days; the range, 2 to 4418 days, was very broad, reflecting the fact that the severity of heart failure varies dramatically. 
  • Older age and also certain findings on an echocardiogram are prognostic for a shorter survival time. 
  • Sudden death, even of an apparently stable patient, is possible.

TREATMENT AND PROGNOSIS: FOR CATS WITH BLOOD CLOTS (ARTERIAL THROMBOEMBOLISM, ATE) DUE TO HCM

  • ATE is a devastating problem. It is so painful, and the prognosis is so poor, that most cats are justifiably euthanized within minutes to hours of diagnosis.
  • Treatment can be attempted, but it is very intensive care, and it is very often not successful.
  • If treatment for ATE succeeds the pet is started on a daily anti-clotting medication. These cats remain at high risk for recurrence of ATE. 
  • Not counting the high percentage of cats with ATE that are euthanized or pass away within the first several hours, the average survival time in one large study was 184 days, with a range of 2 to 2278 days. 

Yarmouth Veterinary Center
2017

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