I don’t know the number of cat health studies that the Winn Feline Foundation Ricky Fund has supported over the years, but certainly since 2002 there have been many. Below is a review of a recent prevalence study led by Dr. Philip Fox, veterinary cardiologist at Animal Medical Center in NY to assess risk of cardiac disease in cats, and study long-term affects.
Our cat, Ricky, a Devon Rex died of sudden death caused by feline hypertrophic cardiomyopathy (HCM), which is by far the most common cause of sudden death in cats and the most common heart disease in cats. In fact, it’s so common that HCM may be the most common cause of death in cats from around the age of two years to 10 years when kidney disease and cancers begin to take over.
Ricky was a rather famous cat in his day, known for his piano playing skills and many other behaviors, from giving “high fives” to jumping through a Hoola Hoop. He was featured on more national TV shows than I can rattle off, from National Geographic Explorer to a PBS show to various Animal Planet Shows. On radio his piano playing was heard on several shows on WGN Radio, Chicago and the late legendary Paul Harvey featured Ricky twice.
Most of all the bond Ricky and I had was so palpable that when he died, I received an outpouring of condolence cards via snail mail. After all, this was mostly before email and pre-YouTube (otherwise he would been a YouTube star).
There were no answers for HCM, so I decided to use my platforms to raise money to learn more, and ultimately hoping to pave the way for a treatment for HCM.
With the money raised, for example, in Maine Coon cats and Ragdolls a simple cheek swab can determine if a gene defect exists for HCM. But we need to do far more.
I set up a Facebook giving page to raise money for HCM for my birthday to support the Winn Feline Foundation Ricky Fund.
We now know the many ways which HCM occurs. Yes, HCM does occur more often within some pedigreed cat breeds. HCM can also be familial in any breed or mix of breed (run genetically within families) or just spontaneously occur. This is important information, but also frustrating that HCM can be difficult even possible to predict. Sometimes the affects (as described below) kill cats and often younger cats, and they just die suddenly without even being previously diagnosed. Those numbers are likely even higher than indicated because outdoor cats who may not return could have been hit by a car, hunted by a coyote but potentially died of HCM.
HCM symptoms may be difficult for cat caretakers to notice because cats can be so stoic. If a veterinarian hears a murmur, that might indicate HCM is occurring but not necessarily. The only solid test is an ultrasound, and a visit to a veterinary cardiologist. Some caretakers can’t afford this (though the price has come down some in recent years), so they never know for sure.
Some cats with HCM throw a painful Arterial Thromboembolism or stroke like event caused by a blood clot(s). Most of these cats, with emergency care, can be treated successfully. But they likely throw more of these Arterial Thromboembolisms. Ultimately, these tend to worsen over time. And even if the heartbreak of seeing their cats in agony doesn’t push clients to euthanize, the cost of repeated emergency treatments might. Other cats ultimately experience heart failure, which can be treated for a time, but those cats do succumb. Or inexplicably some cats with HCM are lucky, and live out a totally normal life – most often with medication – but it’s not only the meds that allow the cat to live out this normal life, the disease – for unknown reasons – just never progresses in these individual cats. Why? No one knows.
We need to know more. And we need to find a treatment for this all TOO COMMON disease. Please help.
Here’s that study information and summary for the Dr. Fox led study:
Hypertrophic Cardiomyopathy (HCM) is the most common heart disease of domestic cats worldwide, and is one of the most common causes of death of cats. HCM is caused primarily by genetic factors, and involves a progressively worsening thickening of the heart muscle that may eventually result in illness and death. The most common forms of disease associated with HCM are Congestive Heart Failure (CHF), which consists of fluid buildup in the lungs and chest space; and Arterial Thromboembolism (ATE), which involves blood clots forming in the heart and lodging in small vessels of the limbs, lungs, brain, or elsewhere. Though this disease can be fatal, a large number of cats are diagnosed in the “subclinical” phase of disease, before signs of illness occur. Despite its high prevalence, little is known about the long-term course of subclinical HCM in cats.
The purpose of this study was to determine the morbidity and survival of cats diagnosed with subclinical HCM when compared to apparently healthy cats. The study was designed as a retrospective, multicenter, longitudinal cohort study. Medical records of cats were reviewed from 50 veterinary hospitals in 21 countries. All investigators were board certified or similarly credentialed cardiologists.
Note that this study differentiated between cats with HCM and cats with the “obstructive” subtype of disease (HOCM), however no significant differences between these groups were found for any variable. For the purposes of this summary, both groups will be referred to together as “HCM”.
Cats were included in this study on the basis of medical and echocardiographic records and interviews with veterinarians and owners. Cats were included in the HCM group of the study if their echocardiograph was consistent with published standards for the diagnosis of HCM (i.e., LV or IVS wall thickness >6mm). Cats were considered ”healthy” based on a normal echocardiogram, or evidence of right ventricular outflow obstruction, or trivial mitral or tricuspid regurgitation. All cats were free of clinical signs of cardiac disease including syncope, CHF or ATE. Cats were also free of heartworm disease, hypertension, renal disease, hyperthyroidism, anemia, or any other disease judged by the veterinarian to impact life expectancy. Cats were required to have outcome assessments available for at least 5 years after enrollment. Data was collected from 2001 through 2016.
Cats were followed for 15 years or until death or loss of follow-up. Death due to CHF, ATE, euthanasia as a result of these conditions, or unexplained sudden death were considered to be cardiac in origin. Sudden death was classified as unanticipated death with no clinical signs in the past 24h.
1730 cats were recruited into the study. Of these cats, 1008 had HCM and 722 were considered healthy. Cats with HCM were older than healthy cats. Most cats diagnosed with HCM clustered in the 1-5 or 5-11 year range, but dropped of significantly after 11y. Both intact and neutered male cats were significantly more common in the HCM group, replicating previous findings suggesting males are at higher risk of HCM. Body weight did not differ between groups. 34 breeds were represented, most commonly Domestic Shorthairs, Maine Coons, Persians, and Norwegian Forest Cats.
Heart murmurs were heard in 82% of HCM cats and 46% of healthy cats. Cats with HCM were more likely to have loud (>3/6) murmurs, while healthy cats were more likely to have quiet (1-2/6) murmurs. Arrhythmias were present in 12.7% of HCM cats and 4.2% of healthy cats. Systolic blood pressure did not differ between groups.
Cardiovascular drugs were prescribed in 52.3% of cats with HCM and 78.2% of cats with HOCM, and no healthy cats. Drugs included beta blockers, ACE-inhibitors, diltiazem, clopidogrel, and aspirin.
Overall, the prevalence and demographics of cats diagnosed with HCM are not unexpected, and largely replicate the results of previous studies, albeit with greater power. The following blog post will review the outcomes of this study and discuss the conclusions of the authors.
30.5% of cats diagnosed with hypertrophic cardiomyopathy (HCM) experienced some type of cardiovascular morbidity over the course of the study. Only 0.97% of healthy cats experienced a cardiac event. 24.2% of HCM cats experienced CHF, and 11.6 ATE. Only 2.2% experienced sudden death. As previously mentioned, there was no significant difference in any measured outcome for HCM vs obstructive (HOCM) groups.
The risk of cardiovascular morbidity and mortality increased at 1, 5, and 10 years after recruitment to the study. Risk of cardiac death was 1 in 15, 1 in 4.4, and 1 in 3.5 at 1, 5, and 10 year points for HCM cats. Risk of cardiac death for healthy cats remained stable at 1 in 100 throughout the study period. Interestingly, the use of cardiovascular medications had no effect on survival through the duration of the study.
30.5% of cats with HCM experienced congestive heart failure (CHF), arterial thromboembolism (ATE), or both, and 27.9% experienced cardiovascular death. This suggests that most cat who experience clinical signs of HCM will die of their disease. Risk for cardiovascular morbidity (CHF/ATE) assessed at 1, 5, and 10 years after study entry was 7.0%/3.5%, 19.9%/9.7%, and 23.9%/11.3%. This suggests that the risk for CHF is consistently ~2x the risk of ATE, though it is important to remember that many cats may experience both CHF and ATE. Risk of cardiac death was 6.7%, 22.8%, and 28.3% respectively at these time points. While risk of CHF increased steadily with age, the risk of ATE has largely plateaued by the third quartile.
One graph is a Kaplan-Meir survival curve in the study showing the survival of cats with HCM compared to healthy cats. It shows a steady decrease in the survival of cats with HCM over the course of time, and suggests that the median survival for a cat with subclinical HCM is 10.9 years.
Graphs from the study show the survival of cats experiencing cardiovascular events. A large portion of cats who have cardiovascular events die within the first few months, however cats that survive a year are likely to have a more prolonged survival. Survival curves for CHF and ATE are similar. The average survival for cats that survived >1 day after diagnosis of HCM or CHF was 1.3 years.
This study reached several significant conclusions based on the data collected from this population. These include clear incidence and risk statistics, indication of the survival times after the onset of clinical signs, and demographic information regarding the effected population.
Perhaps the most interesting conclusion reached was that HCM and HOCM have no difference in survival or morbidity at any point in the study, contrary to data in the human literature. Another significant finding was that the use of cardiovascular medications had no apparent effect on survival in the pre-clinical stage.
While this study was well designed and has significant power due to its large sample size and breadth of recruitment, it also has several drawbacks. The retrospective nature of the study presents some limitations and sources of potential bias that could be minimized with a prospective design. The lack of standardization of treatment protocols also presents a potential source of error, as even though there was no overall benefit to survival, stratification into specific therapies was not performed. Lastly, the large number of individual investigators may have led to varying classifications of disease.
Overall, this study provides valuable high level survival and morbidity data on cats with naturally occurring HCM. Its large enrollment numbers and multinational scope allow for valuable epidemiologic data to be collected.
Fox PR, Keene BW, Lamb K, Schober KA, Chetboul V, et al. International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study. J Vet Intern Med. 2018 Apr 16. (Winn Funded Study, W09-017)