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Heart disease: time to take cats seriously

Heart disease: time to take cats seriously

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Luis Fuentes V1. Heart disease: time to take cats seriously // J Vet Cardiol. 2015 Dec;17 Suppl 1:S2-5.

KEYWORDS: Biomarkers; Cardiac; Cardiomyopathy; Echocardiography; Feline

KEYWORDS - Cardiomyopathy; Echocardiography; Biomarkers; Cardiac; Feline

Heart disease in cats has always received less attention than heart disease in dogs. A PubMed search of the last 10 years showed that the Journal of Veterinary Cardiology featured over four times the number of articles relating to dogs than cats. This species bias is not limited to cardiology. Over the same period the Journal of Veterinary Internal Medicine published approximately three times as many articles on canine topics as feline. Cats are consistently under-represented in the veterinary literature.

Possible explanations for the species bias include differences in prevalence of heart disease, mortality rates, popularity as pets, or differences in the attitudes of owners or veterinarians. Additional possibilities include poorer research funding for feline studies, and less interest from the pharmaceutical industry in developing molecules aimed at feline heart disease . Which of these factors is most likely to be responsible?

Disease prevalence studies in dogs and cats are notoriously difficult to conduct without introducing selection bias, and studies are difficult to compare because of differences in methodology and the types of disease. Myxomatous mitral valve disease is widely accepted to be the most common type of heart disease in dogs, although depending on breed and age, prevalence estimates vary widely from 3.5% in the general population to close to 100% in geriatric dogs.1-3 There are no comparable studies of cardiomyopathy in cats, which is the most common feline heart disease. Paige et al.4 reported a 15.5% prevalence of cardiomyopathy in 103 apparently healthy cats, and Wagner et al.5 reported a prevalence of at least 15.6% in 199 shelter cats. In this issue, Payne et al. report a remarkably similar cardiomyopathy prevalence of 14.7% in 780 apparently healthy shelter cats. Based on our current knowledge, heart disease may not be any less common in cats than dogs, so this does not explain the lack of representation in the veterinary literature.

The perception that owners are more reluctant to spend money on veterinary fees for cats compared to dogs may be less common among veterinarians than it used to be. Nevertheless, the 2012 American Veterinary Medical Association report on US pet ownership reported an average household veterinary expenditure on dogs of $378 per year, compared with only $191 on cats.8 Pet demographics are changing; cats now outnumber dogs as pets in many countries. The same American Veterinary Medical Association report estimated that in 2012 there were 74.1 million cats in the US, compared with 69.9 million dogs. The European Pet Food Industry Federation reports a similar picture, with cats outnumbering dogs in many countries in Europe, including the UK, France and Germany. This means that despite the fact that there are more cats than dogs, with a probably similar prevalence of heart disease and at least equivalent cardiac mortality rates, owners are spending less on veterinary care for cats than dogs . Reynolds et al.9 revealed some interesting insights into one possible explanation in a survey of owner attitudes to quality of life in cats with heart disease. The majority of owners perceived hospital visits as extremely stressful for their cat, a factor which might increase owner reluctance to seek veterinary attention unless absolutely necessary.

There have been no specific studies evaluating the recommendations of primary care veterinar¬ians for dogs or cats with suspected heart disease, but there are many reasons why veterinarians might have a lower level of confidence in making diagnostic or therapeutic recommendations for cats, quite apart from the decreased availability of veterinary studies on feline heart disease. While dogs with myxomatous mitral valve disease are readily identifiable with auscultation, a heart murmur is an unreliable indicator of cardiomyop¬athy in cats.5

Electrocardiography and radiography are relatively insensitive tests for the detection of clinically significant cardiomyopathy,10,11 and echocardiography in cats is undoubtedly challenging. Furthermore, even trained cardiologists with excellent echocardiography skills may disagree on the criteria for diagnosing cardiomyopathy. Uncertainty about the ideal practical approach to diagnostic workup might lead some veterinarians to adopt a 'laissez-faire’ approach, often with apparently minimal consequences considering many cats with hypertrophic cardio¬myopathy (HCM) will have long survival times.12-14 This might be compounded by the experience of veterinarians who refer cats with a murmur for echocardiography, only to discover that the cat was in fact normal, and the murmur is functional. Yet there is potential risk in delaying investigations until clinical signs develop, particularly if a cat develops aortic thromboembolism (ATE) as the first presenting sign.

It is clear that there is a need for improved gen¬eral practitioner confidence in clinical decision¬making, particularly in recognizing heart failure in cats with clinical signs, and identifying asymptom¬atic cats at high risk for congestive heart failure (CHF) or ATE. In terms of diagnostic tests available, physical examination is probably under-valued as an audible gallop sound has useful prognostic value,15 but there is increasing evidence that biomarkers offer a practical first step in both these clinical situations, particularly with the recent introduction of a point-of-care NT-proBNP test.16-22

Our understanding of prognosis in cats with cardiomyopathy has greatly improved over the past two decades, with left atrial enlargement consistently remaining a key indicator of risk of CHF and ATE.12-15,23 Even if general echocardio- graphic skills remain beyond the reach of most practitioners, a basic assessment of left atrial size may be feasible,24 particularly with the rise of the focused thoracic ultrasound examination.25 Using a combination of physical exam, biomarkers, and focused ultrasound, it should now be an achievable goal for general practitioners to identify the 'high risk’ preclinical cat or the cat with heart failure, although differentiating cats with subtle cardiomyopathy changes from normal cats will remain a problem for all of us.

Sadly, the therapeutic options for cats with heart disease remain very limited. There is a scarcity of evidence to support any specific therapeutic intervention, both in preclinical cats and cats with CHF. Well-designed studies have been reported, but unfortunately without positive re¬sults.26,27 Rishniw and Pion28 reported on a survey of approaches to treatment of HCM among veterinary cardiologists and concluded that the level of evidence supporting most treatment of HCM in cats is very low. The 'FatCat’ study reported in this issue is a rare example of a double-blinded randomized clinical trial in cats with heart disease. The results show that clopidogrel is superior to aspirin in the prevention of recurrence of ATE, lending support for the use of clopidogrel in cats at high risk ATE and providing a powerful incentive for identifying preclinical 'high risk’ cats likely to benefit from an effective anti-thrombotic treatment. We desperately need more studies on which to base our therapeutic decisions, although suc¬cessful treatment may depend on a better under¬standing of the pathogenesis of HCM. This should be a priority area for study. In the meantime, ineffective medications should not be considered harmless if the quality of life of cats and owners is negatively affected.

This feline issue of the Journal of Veterinary Cardiology is wholeheartedly welcomed. There is no justifiable reason for fewer studies to be re¬ported in cats, particularly as there is so much work to be done in nearly every aspect of cardiomyopathy. Encouraging primary care veterinarians to identify high risk cats will not only benefit their patients but may provide more opportunities for study. Hopefully the tide is turning with this issue, and soon feline heart disease will no longer be thought of as a minority interest.


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