Point-of-care N-terminal pro B-type natriuretic peptide assay to screen apparently healthy cats for cardiac disease in general practice

Should we be screening cats for cardiomyopathy? If so, how?

Occult feline hypertrophic cardiomyopathy (HCM) can result in unexpected sudden death or congestive heart failure (CHF) following routine interventions such as anesthesia, fluid administration, or, potentially, administration of corticosteroids. Consequently, clinicians would like to be able to screen at-risk cats to detect occult HCM and either avoid the risky intervention or attempt to reduce the risk of death or CHF. Currently, the feline N-terminal-proBrain natriuretic peptide test is the only potential screening test for detecting occult HCM. However, some cardiologists have pointed out the poor sensitivity of the test precludes its use as a screening test. This interpretation appears somewhat flawed. Using the current rapid test will allow clinicians to correctly identify half of the cats with moderate-to-severe occult HCM. A small number of cats without HCM will also test positive, necessitating an ultimately needless echocardiographic evaluation to demonstrate their disease-free status. However, the low prevalence of HCM in the general cat population and the apparently much lower rate of adverse events than would be predicted brings into question whether clinicians should bother screening. Therefore, until a more sensitive and accurate screening test becomes available, clinicians will have to decide for themselves whether identifying half of the at-risk cats of sudden death and CHF with this test is better than identifying none of them.

The Feline Cardiomyopathies: 1. General concepts

PRACTICAL RELEVANCE

The feline cardiomyopathies are the most prevalent type of heart disease in adult domestic cats. Several forms have been identified (see Parts 2 and 3), with hypertrophic cardiomyopathy (HCM) being the most common. Clinically the cardiomyopathies are often indistinguishable. Cats with subclinical cardiomyopathy may or may not have characteristic physical examination findings (eg, heart murmur, gallop sound), or radiographic cardiomegaly. Cats with severe disease may develop signs of heart failure (eg, dyspnea, tachypnea) or systemic arterial thromboembolism (ATE; eg, pain and paralysis). Sudden death is possible. Treatment usually does not alter the progression from subclinical to clinical disease and often the treatment approach, once clinical signs are apparent, is the same regardless of the type of cardiomyopathy. However, differentiating cardiomyopathy from normal variation may be important prognostically.

PATIENT GROUP

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. Mixed-breed cats are most commonly affected but certain breeds are disproportionately prone to developing HCM.

DIAGNOSTICS

Subclinical feline cardiomyopathies may be suspected based on physical examination findings, thoracic radiographs and cardiac biomarker results but often the disease is clinically silent. The definitive clinical confirmatory test is echocardiography. Left heart failure (pulmonary edema and/or pleural effusion) is most commonly diagnosed radiographically, but point-of-care ultrasound and amino terminal pro-B-type natriuretic peptide (NT-proBNP) biomarker testing can also be useful, especially when the stress of taking radiographs is best avoided.

KEY FINDINGS

Knowledge of pathophysiological mechanisms helps the practitioner identify the feline cardiomyopathies and understand how these diseases progress and how they manifest clinically (heart failure, ATE). Existing diagnostic tests have strengths and limitations, and being aware of these can help a practitioner deliver optimal recommendations regarding referral.

CONCLUSIONS

Several types of feline cardiomyopathies exist in both subclinical (mild to severe disease) and clinical (severe disease) phases. Heart failure and ATE are the most common clinical manifestations of severe cardiomyopathy and are therapeutic targets regardless of the type of cardiomyopathy. The long-term prognosis is often guarded or poor once overt clinical manifestations are present.

AREAS OF UNCERTAINTY

Some cats with presumed cardiomyopathy do not have echocardiographic features that fit the classic cardiomyopathies (cardiomyopathy - nonspecific phenotype). Although no definitive treatment is usually available, understanding how cardiomyopathies evolve remains worthy of investigation.

The Feline Cardiomyopathies: 2. Hypertrophic cardiomyopathy

Practical relevance:

Hypertrophic cardiomyopathy (HCM) is the most common form of feline cardiomyopathy observed clinically and may affect up to approximately 15% of the domestic cat population, primarily as a subclinical disease. Fortunately, severe HCM, leading to heart failure or arterial thromboembolism (ATE), only occurs in a small proportion of these cats.

Patient group:

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. A higher prevalence in male and domestic shorthair cats has been reported.

Diagnostics:

Subclinical feline HCM may or may not produce a heart murmur or gallop sound. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM. Biomarkers should not be relied on solely to diagnose the disease. While severe feline HCM can usually be diagnosed via echocardiography alone, feline HCM with mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion, which means there is no definitive test for HCM in these cats and so other disorders that can cause mild to moderate LV wall thickening (eg, hyperthyroidism, systemic hypertension, acromegaly, dehydration) need to be ruled out.

Key findings:

While a genetic cause of HCM has been identified in two breeds and is suspected in another, for most cats the cause is unknown. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction (DLVOTO) and, in turn, the most common cause of a heart murmur with feline HCM. While severe DLVOTO is probably clinically significant and so should be treated, lesser degrees probably are not. Furthermore, since SAM can likely be induced in most cats with HCM, the distinction between HCM without obstruction and HCM with obstruction (HOCM) is of limited importance in cats. Diastolic dysfunction, and its consequences of abnormally increased atrial pressure leading to signs of heart failure, and sluggish atrial blood flow leading to ATE, is the primary abnormality that causes clinical signs and death in affected cats. Treatment (eg, loop diuretics) is aimed at controlling heart failure. Preventive treatment (eg, antithrombotic drugs) is aimed at reducing the risk of complications (eg, ATE).

Conclusions:

Most cats with HCM show no overt clinical signs and live a normal or near-normal life despite this disease. However, a substantial minority of cats develop overt clinical signs referable to heart failure or ATE that require treatment. For most cats with clinical signs caused by HCM, the long-term prognosis is poor to grave despite therapy.

Areas of uncertainty:

Genetic mutations (variants) that cause HCM have been identified in a few breeds, but, despite valiant efforts, the cause of HCM in the vast majority of cats remains unknown. No treatment currently exists that reverses or even slows the cardiomyopathic process in HCM, again despite valiant efforts. The search goes on.

Point-of-care N-terminal pro B-type natriuretic peptide assay to screen apparently healthy cats for cardiac disease in general practice

Background

Point‐of‐care (POC) N‐terminal pro B‐type natriuretic peptide (NT‐proBNP) ELISA test has been evaluated for screening cats for cardiac disease in the referral veterinary setting but less is known about its use in general practice (GP).

Objectives

To evaluate the diagnostic utility of a POC NT‐proBNP ELISA in cats seen in GPs.

Animals

Two hundred and seventeen apparently healthy cats from 21 GPs.

Methods

This was a prospective, cross‐sectional study. Cardiac auscultation and POC NT‐proBNP ELISA were done by veterinarians at their GPs. After enrollment at GPs, cats were sent to a cardiology referral hospital for cardiac auscultation and echocardiographic diagnosis. Results were interpreted based on whether cats had normal or abnormal echocardiographic findings.

Results

Point‐of‐care NT‐proBNP ELISA results differentiated cats in the abnormal group from those in the normal group with a sensitivity of 43%, specificity of 96%. In cats with a heart murmur at GPs, POC NT‐proBNP ELISA results differentiated cats in the abnormal group from those in the normal group with a sensitivity of 71% and a specificity of 92%.

Conclusion and Clinical Importance

In apparently healthy cats in GPs, positive POC NT‐proBNP results are associated with heart disease, warranting an echocardiogram, but negative results do not reliably exclude heart disease. These results suggest POC NT‐proBNP is not an effective screening test for apparently healthy cats in GPs, although its performance is improved if it is used only in cats that have a heart murmur.