Introduction
Heart disease in cats is a significant and insidious health concern that often progresses silently—unnoticed by owners and veterinarians—until decompensation causes heart failure, sudden death, or other dramatic clinical events. Despite advances in veterinary diagnostics, the true burden of heart disease among cats remains under-recognized, particularly because so much of it lies below the threshold of clinical detection (so-called “occult” disease). As the use of NT-proBNP testing grows for identifying cats with cardiac pathology, a nuanced understanding of disease prevalence, risk stratification, and diagnostic principles (notably, the base rate or base rate neglect fallacy) is essential for practitioners to avoid misinterpretation and ensure optimal feline care.
Prevalence and Types of Feline Heart Disease
Feline heart disease, especially hypertrophic cardiomyopathy (HCM), is disturbingly common. HCM is characterized by left ventricular muscle thickening, which impairs relaxation and filling and can predispose to congestive heart failure, thromboembolism, and sudden death[1][2].
Epidemiology
The prevalence of heart disease in the general cat population is remarkably consistent across multiple studies. Payne et al. found a prevalence of 14.7% in 780 shelter cats[3][4], while Wagner et al. reported 15.6% in 199 healthy cats, and Paige et al. found 15.5% in 103 healthy cats[4]. These figures align with broader estimates that place the risk of heart disease in healthy-appearing cats between 14% and 34%[1].
Hypertrophic cardiomyopathy represents the most common form, accounting for approximately 60% of cardiomyopathy cases referred for echocardiography[5]. In apparently healthy cats screened for cardiomyopathy, HCM is by far the most prevalent form[5][2]. Other cardiomyopathies are much less common, with restrictive and dilated forms having prevalences under 1%[1].
The Silent Epidemic: Occult Heart Disease
A particularly concerning aspect of feline heart disease is its tendency to remain occult or asymptomatic. Multiple studies have demonstrated that a substantial percentage of cats remain entirely asymptomatic despite clear echocardiographic abnormalities. In one Malaysian study of apparently healthy cats, 40.7% were found to have heart disease[6]. Another study found that up to 41% of apparently healthy cats had occult disease[4].
The presence of a heart murmur does not always correspond to structural disease, yet when murmurs are detected in otherwise asymptomatic cats, the likelihood of underlying pathology increases substantially. Studies have shown that 53% of cats with murmurs actually have echocardiographic evidence of cardiac disease[6][4], and in some populations, as many as 86% of asymptomatic cats with murmurs were found to have underlying heart disease on echocardiography[3].
Demographic and Breed-Related Risk Factors
The risk of feline heart disease is not evenly distributed across the population. Important demographic risk factors have been clearly established through multiple research studies.
Age
HCM most commonly manifests in adult cats, with studies showing a mean age at diagnosis around 6.5 years[6]. However, the condition exists from kittenhood through geriatrics, and risk generally increases with advancing age[4]. Cats can be diagnosed at any life stage, with age ranges in studies spanning from 7 months to 19 years[6].
Sex
Male cats are substantially more likely to develop HCM than females. Multiple studies have demonstrated this sex predisposition, with one study showing that 45% of male cats versus 33% of female cats were diagnosed with cardiomyopathy[6]. The male preponderance is consistent across different populations and remains regardless of neuter status[1].
Breed
Certain breeds exhibit markedly increased risk for heart disease. Maine Coons, Ragdolls, and British Shorthairs are particularly predisposed to HCM[1][4]. Familial occurrence has been observed in mixed-breed cats[6], Persian cats[6], and British Shorthair cats, while specific genetic mutations have been identified in Maine Coon cats with HCM[6].
While most cases in general population studies occur among domestic (mixed-breed) cats due to their numerical predominance, the proportional prevalence is highest in specific predisposed breeds[1][4]. In Maine Coons, for example, 30-40% carry the mutation associated with HCM, though only 3-5% are homozygous for the mutation and at highest risk for severe disease[5][2].
Other Factors
Research has found no consistent relationship between heart disease risk and factors such as body weight or coat color[6]. Tricolor cats appear underrepresented in affected populations, likely reflecting the overall male bias for the disease[6].
Diagnostic Challenges: Beyond the Stethoscope
Routine examination and auscultation are not reliable for detecting feline heart disease. Heart murmurs often arise from non-pathological (“innocent” or “functional”) causes, while true structural pathology can exist without any audible abnormality[4]. Physical examination alone has been shown to be unreliable in diagnosing cardiomyopathy in cats[6].
Studies have demonstrated the limitations of traditional screening methods. In one study, among apparently healthy cats with normal heart sounds, 31.4% were subsequently diagnosed with cardiomyopathy[6]. Conversely, vertebral heart scale measurements, commonly used to assess heart size on radiographs, showed no association with the presence of cardiomyopathy[6].
Only advanced imaging—primarily echocardiography—can reliably identify both overt and occult disease[6][4]. For high-risk populations (especially at-risk breeds, adults, and males), annual or even more frequent screening echocardiograms are often recommended by specialists[4]. However, cost, accessibility, and owner acceptance remain limiting factors.
The Role and Interpretation of NT-proBNP Testing
To supplement the limitations of clinical and imaging-based screening, NT-proBNP testing—a marker of cardiac wall stretch—has emerged as a potentially valuable diagnostic tool[3][7]. NT-proBNP is released from the ventricles in response to stretch or stress, and with cardiac disease, the amount released is proportional to disease severity[8].
However, like all diagnostic tests, the accuracy of NT-proBNP in ruling disease in or out critically depends on:
- The disease’s prevalence in the tested group
- The test’s sensitivity (the chance a diseased animal tests positive)
- Its specificity (the chance a healthy animal tests negative)
Test Performance by Population
The performance characteristics of NT-proBNP vary significantly depending on the population being tested:
- Healthy/asymptomatic cats: Sensitivity ~43%, specificity ~96%[3]
- Cats with murmurs: Sensitivity ~71%, specificity ~92%[3]
- Cats with possible heart failure: Sensitivity >90%, specificity ~87-90%[9]
When interpreting NT-proBNP results in cats with normal cardiac auscultation findings, the sensitivity drops to 31% and specificity remains high at 97%[10]. This variation in test performance based on the clinical context is crucial for proper interpretation.
The Base Rate Fallacy: A Critical Diagnostic Pitfall
Failure to account for disease prevalence when interpreting test results is known as the base rate fallacy or base rate neglect[11][12]. This cognitive bias occurs when people misjudge an outcome by giving too much weight to test-specific characteristics while overlooking the crucial baseline probability of disease in the population being tested[11].
Understanding the Mathematics
The base rate fallacy can be illustrated through precise calculations using different feline populations. Let’s examine two scenarios using established test characteristics and disease prevalences.
Scenario 1: Testing the General Population of Healthy Cats
Parameters:
- Disease prevalence: 15%
- NT-proBNP sensitivity: 43%
- NT-proBNP specificity: 96%
Calculations for 1,000 cats:
In a population of 1,000 randomly selected healthy-appearing cats:
- 150 cats actually have heart disease
- 850 cats are truly healthy
Test Results:
- True positives: 64 cats (diseased cats correctly identified)
- False negatives: 86 cats (diseased cats missed by the test)
- True negatives: 816 cats (healthy cats correctly identified)
- False positives: 34 cats (healthy cats incorrectly flagged)
Interpretation:
- Positive Predictive Value (PPV): 65.5% – If the test is positive, there’s about a 2 in 3 chance the cat actually has heart disease
- Negative Predictive Value (NPV): 90.5% – If the test is negative, there’s about a 9 in 10 chance the cat is truly healthy
Scenario 2: Testing Cats With Heart Murmurs
Parameters:
- Disease prevalence: 53%
- NT-proBNP sensitivity: 71%
- NT-proBNP specificity: 92%
Calculations for 1,000 cats with murmurs:
- 530 cats actually have heart disease
- 470 cats are truly healthy despite the murmur
Test Results:
- True positives: 376 cats
- False negatives: 154 cats
- True negatives: 432 cats
- False positives: 38 cats
Interpretation:
- Positive Predictive Value (PPV): 90.9% – A positive test now strongly suggests disease
- Negative Predictive Value (NPV): 73.8% – A negative test is less reassuring in this higher-risk group
The Impact of Base Rate on Clinical Decision-Making
These calculations reveal the profound impact of disease prevalence on test interpretation:
| Cat Population | Prevalence | PPV | NPV | Clinical Implication |
| Healthy cats | 15% | 65.5% | 90.5% | Positive results need confirmation; negative results fairly reassuring |
| Cats with murmurs | 53% | 90.9% | 73.8% | Positive results highly suggestive; negative results less definitive |
Clinical Implications of the Base Rate Fallacy
In low-prevalence populations (healthy cats):
- Clinicians may overdiagnose disease based on positive results
- One-third of positive tests represent false positives
- This can lead to unnecessary anxiety, treatments, and costs
In high-prevalence populations (cats with murmurs or clinical signs):
- Clinicians may underestimate disease risk with negative results
- About one-quarter of negative tests miss actual disease
- This can lead to false reassurance and delayed diagnosis
Avoiding the Base Rate Fallacy: Best Practices
1. Context-Dependent Interpretation
Always interpret NT-proBNP results within the clinical context and with understanding of disease prevalence in the tested group[3][7]. The same test result means different things in different populations.
2. Use as Screening, Not Diagnostic
NT-proBNP should be used as a screening or adjunctive test—not as a stand-alone diagnostic[7][8]. Abnormal results should prompt further investigation, typically with echocardiography.
3. Consider Risk Factors
Remember that breed, age, and sex matter significantly[1][4]. Maine Coon or Ragdoll males deserve more vigilant screening than random-source females, regardless of test results.
4. Understand Limitations
Recognize that negative results don’t completely rule out disease, especially in high-risk populations[3][10]. The test’s relatively low sensitivity means that significant disease can be missed.
Advanced Diagnostic Considerations
NT-proBNP Performance in Special Populations
Recent research has provided additional insights into NT-proBNP performance:
- In cats with renal infarction, occult heart disease was found in a higher proportion, with an odds ratio of 2.4 for increased risk[13][14]
- The test shows improved performance when used in conjunction with other clinical findings[7][8]
- Point-of-care NT-proBNP ELISA has been specifically evaluated for use in general practice settings[3][10]
Comparison with Other Cardiac Biomarkers
While NT-proBNP is the most studied cardiac biomarker in cats, cardiac troponin I (cTnI) also provides valuable information[15]. Cardiac troponins are quantitative markers of myocardial injury that provide prognostic information regardless of clinical presentation[15]. The combination of biomarkers may provide enhanced diagnostic accuracy compared to single tests.
The Natural History and Prognosis
Understanding the natural history of feline heart disease helps contextualize the importance of accurate diagnosis. Most cats with HCM never exhibit clinical signs in their lifetime[4]. However, the disease is extremely heterogeneous in both presentation and outcome.
A longitudinal study of cats from rehoming centers found that HCM in cats not referred for suspected heart disease is associated with a low rate of cardiovascular events[16]. The study monitored cats for a median of 5.6 years, providing valuable insights into disease progression in apparently healthy cats.
Cardiac mortality data from insurance studies report overall cardiac mortality of 30 deaths per 10,000 cat years[4]. For cats diagnosed with HCM, median survival time is 5.9 years for cardiac mortality[4]. The major clinical manifestations include congestive heart failure (56/107 cats), thromboembolic complications (34 cats), and sudden death (17/107 cats) in one retrospective study[4].
Future Directions and Research Needs
Several areas warrant continued investigation:
Genetic Testing Integration
As genetic mutations associated with HCM in specific breeds become better understood, incorporating genetic testing with biomarker screening may improve diagnostic accuracy[1][5].
Biomarker Combinations
Research into combinations of cardiac biomarkers, potentially including both NT-proBNP and cardiac troponin I, may provide enhanced diagnostic performance[15][8].
Population-Specific Cut-offs
Development of population-specific reference ranges and cut-off values based on breed, age, and sex may improve test interpretation[7][8].
Longitudinal Studies
Additional longitudinal studies tracking the progression from occult to clinical disease will help refine screening protocols and treatment recommendations[16].
Economic and Welfare Considerations
The high prevalence of occult heart disease raises important questions about screening strategies. While echocardiography remains the gold standard, its cost and limited availability make population-wide screening challenging[4]. NT-proBNP testing, despite its limitations, offers a more accessible screening option that can help identify cats warranting further evaluation.
The negative predictive value of NT-proBNP is particularly valuable in clinical practice. When the test is negative in low-risk populations, it provides reasonable reassurance that significant heart disease is unlikely[3][10]. This can help guide resource allocation and reduce unnecessary procedures.
Educational Implications
The base rate fallacy in NT-proBNP interpretation highlights broader educational needs in veterinary medicine:
For Veterinarians
- Understanding of basic biostatistics and test interpretation
- Appreciation of how disease prevalence affects diagnostic accuracy
- Integration of multiple clinical factors in decision-making
For Cat Owners
- Awareness of heart disease prevalence in cats
- Understanding of risk factors, particularly breed and sex predispositions
- Recognition that normal clinical examinations don’t rule out heart disease
Conclusion
Feline heart disease is common, frequently silent, and often missed by routine examinations. The risk is greatest in males, certain purebred cats, and increases with age[1][6][4]. Early, accurate diagnosis is essential but challenging; the NT-proBNP assay is a helpful adjunct but is vulnerable to misinterpretation unless the clinician accounts for both test characteristics and the background prevalence of disease—the base rate.
The base rate fallacy represents a significant cognitive bias that can lead to both overdiagnosis in low-risk populations and underdiagnosis in high-risk groups[11][17]. Understanding this fallacy, along with judicious, context-sensitive testing and imaging, is essential for optimal management and for reducing the burden of unrecognized feline heart disease.
Key takeaways for clinical practice include:
- Disease prevalence fundamentally alters test interpretation – the same result means different things in different populations
- NT-proBNP is most valuable as a screening tool – not a standalone diagnostic test
- Risk stratification matters – breed, age, and sex significantly influence disease probability
- Negative results are not absolute – especially in high-risk populations
- Echocardiography remains essential – for definitive diagnosis and disease staging
As our understanding of feline heart disease continues to evolve, the integration of clinical assessment, biomarker testing, and advanced imaging—interpreted within the appropriate clinical context—offers the best approach to managing this common but often occult condition. Awareness of diagnostic biases, particularly the base rate fallacy, is not just statistical pedantry but a safeguard against misdiagnosis and a pathway to better feline care.
The silent epidemic of feline heart disease challenges traditional veterinary approaches and demands proactive strategies that account for the complex interplay between test characteristics, disease prevalence, and clinical decision-making. Only through such comprehensive understanding can we hope to improve outcomes for the substantial number of cats affected by this important condition.
References
- https://pmc.ncbi.nlm.nih.gov/articles/PMC5574284/
- https://journals.sagepub.com/doi/10.1177/1098612X211021819
- https://www.sciencedirect.com/science/article/abs/pii/S1760273415000685
- https://www.veterinary-practice.com/article/heart-disease-in-cats-identifying-and-managing-feline-heart-disease-in-practice
- https://pmc.ncbi.nlm.nih.gov/articles/PMC8723176/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7521808/
- https://www.tandfonline.com/doi/full/10.1080/00480169.2024.2404684
- https://fvma.org/using-cardiac-biomarkers-in-clinical-practice/
- https://bmcvetres.biomedcentral.com/articles/10.1186/s12917-017-1319-6
- https://pmc.ncbi.nlm.nih.gov/articles/PMC8295655/
- https://statisticsbyjim.com/probability/base-rate-fallacy/
- https://cacm.acm.org/blogcacm/the-base-rate-neglect-cognitive-bias-in-data-science/
- https://pubmed.ncbi.nlm.nih.gov/40275464/
- https://onlinelibrary.wiley.com/doi/10.1111/jvim.70107?af=R
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4913658/
- https://onlinelibrary.wiley.com/doi/10.1111/jvim.16576
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6693499/
