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)
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. Due to the extent of this study, results will be discussed in two parts.
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. (MRK)