N-Terminal Atrial Natriuretic Peptide Immunoreactivity in Plasma of Cats with Hypertrophic Cardiomyopathy

Updates on Laboratory Evaluation of Feline Cardiac Diseases

Laboratory tests can be altered in cardiovascular diseases and the investigation of specific tests or biomarkers may provide additional information about myocardial damage. Traditional laboratory tests, such as cell blood count, serum biochemistry, and coagulation, can be useful in investigating patients, but are not specific. However, markers like Troponin and Natriuretic Peptides may possibly furnish further data on myocardium damage and can be used in both studying and monitoring cats with cardiac disease. Moreover, the evaluation of the thyroid profile is very important as hyperthyroid cats concomitant cardiovascular diseases are very common and they can also be a direct consequence of endocrinopathy. The purpose of this manuscript is to provide the widest possible overview of what is present in the literature about the feline clinical pathology of heart diseases through a rational division of the main alterations of traditional tests and biomarkers.

Diagnostic accuracy of plasma atrial natriuretic peptide concentrations in cats with and without cardiomyopathies

OBJECTIVES

Plasma atrial natriuretic peptide (ANP) levels have been reported to be elevated in cats with cardiomyopathy. We investigated the diagnostic accuracy of plasma ANP concentration as an indicator of the severity of cardiomyopathies.

ANIMALS

This study included 78 control cats and 83 cats with various types of cardiomyopathy.

METHODS

This was a prospective multicentre study. Control cats were determined to have a normal heart, and diseased cats were diagnosed by echocardiography. Diseased cats were divided into asymptomatic cats without left atrial dilation (LAD), asymptomatic cats with LAD, and cats with heart failure. Plasma C-terminal ANP concentrations were measured using chemiluminescence.

RESULTS

The median plasma ANP concentration in controls was 43.3 (interquartile range, 33.0-56.3) pg/mL. Plasma ANP values were significantly higher in the cardiomyopathic cats with LAD and heart failure, but the values in cats without LAD were comparable to those in control cats. To distinguish cats with cardiomyopathy from controls, a plasma ANP concentration >77.5 pg/mL afforded sensitivity of 66.3% and specificity of 84.6%. Use of plasma ANP concentration >110.9 pg/mL to identify cats with LAD had a sensitivity of 73.6% and specificity of 93.5%. The areas under the receiver-operating characteristic curve were 0.80 and 0.86.

CONCLUSIONS

Plasma ANP concentrations were higher in cats with more advanced cardiomyopathy. Although assaying the ANP concentration alone may not help to diagnose cardiac disease, measuring provides additional information that is useful for assessing the severity of cardiomyopathies.

ProANP as a screening biomarker for hypertrophic cardiomyopathy in Maine coon cats

The aim of this study was to determine if atrial natriuretic peptide can be used as an early screening tool for hypertrophic cardiomyopathy in Maine coon cats.

ANIMALS

The study was performed in 43 Maine coon cats of both sexes, aged 11 to 92 months. Clinical and echocardiographic examinations were done and proANP serum concentrations were measured every three months over a period of one year (each cat had a total of five examinations). Cats were divided into 3 groups based on echocardiographic results: group 1 - healthy cats, group 2 - cats with unequivocal hypertrophic cardiomyopathy results, group 3 - cats with HCM. The study showed that the concentration of atrial natriuretic peptide correlates with the severity of HCM. A significant increase in serum concentration of this peptide was observed in cats from group 3, but it did not differ significantly between cats from group 2 and the healthy animals (p>0.05). A correlation was also found between proANP and age of the cats (p<0.01, r=0.5578) as well as between the ejection fraction (p=0.0285, r=0.5305) and end-systolic left ventricular diameter (p=0.05, r=0.48) in the affected animals. Atrial natriuretic peptide may be used to help in the diagnosis of advanced stages of HCM in Maine coon cats. Cats with high levels of proANP should be assigned to echocardiographic studies to confirm the disease.

Cardiac biomarkers in cats

Cardiac biomarkers have been used in cats as part of the clinical assessment of heart disease for over a decade. They are widely available to practitioners through commercial reference laboratories. The evidence base for the use of cardiac biomarkers (primarily N-terminal pro-B type natriuretic peptide and cardiac troponin I) in cats is comprehensively reviewed in this article, focusing on each of six specific areas: distinguishing cardiac from non-cardiac causes of respiratory distress; measurement of cardiac biomarkers in urine and pleural fluid; identification of occult cardiomyopathy; effects of systemic disease on circulating concentrations of cardiac biomarkers; point-of-care biomarker testing, and the possible prognostic utility of cardiac biomarker measurement.

Circulating natriuretic peptide concentrations in hyperthyroid cats

OBJECTIVES

To assess the influence of thyroid function on natriuretic peptide concentration in hyperthyroid cats before and after treatment.

METHODS

Serum natriuretic peptide concentration was measured in 61 hyperthyroid cats recruited from first-opinion clinics before and after treatment.

RESULTS

Following successful treatment, total thyroxine, heart rate, systolic blood pressure and packed cell volume all decreased and bodyweight and creatinine concentrations increased. Furthermore, a significant (P < 0·001) decline in NT-proBNP concentration but not NT-proANP was identified.

CLINICAL SIGNIFICANCE

Thyroid function has a modest but significant effect on NT-proBNP concentration. Thyroid status should be taken into account when interpreting NT-proBNP concentrations in cats.

Comparison of auscultatory and echocardiographic findings in healthy adult cats

OBJECTIVES

This pilot study was performed to investigate murmur prevalence and to explore the association between auscultatory and echocardiographic findings in apparently healthy cats in order to design a larger study.

ANIMALS, MATERIALS AND METHODS

Adult cats in 4 rehoming centres were screened by auscultation and echocardiography (echo) over 2 periods of 2 weeks each. In the first period, echo was attempted only in cats with murmurs. In the second period, all cats underwent auscultation by 2 observers and echo. LVH was defined in 5 ways: maximal diastolic left ventricular (LV) wall thickness ≥ 6 mm or ≥ 5.5 mm with 2D (LVH(6 2D), LVH(5.5 2D), respectively) or M-Mode echo (LVH(6 MM) or LVH(5.5 MM) respectively), or LV wall thickness ≥ 6 mm (2D) for >50% of a wall segment (LVH(50%)).

RESULTS

67/199 (34%) cats had a murmur. Interobserver agreement on murmur presence was moderate (κ 0.47). 61 cats with a murmur and 31 cats without underwent both auscultation and echo. Depending on the criteria, LVH was present in 31 (LVH(6 2D)), 21 (LVH(50%)) and 11 (LVH(6 MM)) scanned cats. 18-62% of cats with murmurs had LVH, depending on the echo criteria used. Agreement was best between observers in identifying LVH using LVH(6 2D) and LVH(50%) (κ = 1.0).

CONCLUSIONS

Heart murmurs are common in apparently healthy cats. The prevalence of LVH varies depending on the criteria used.

NT-proBNP measurement fails to reliably identify subclinical hypertrophic cardiomyopathy in Maine Coon cats

The purpose of this study was to evaluate the value of measuring plasma NT-proBNP concentration as a screening tool in cats with varying severity of subclinical hypertrophic cardiomyopathy (HCM). Plasma NT-proBNP concentration was measured in 35 cats that had previously been classified as normal, equivocal, moderate HCM or severe HCM via echocardiography. No cat had ever been in congestive heart failure. Cats with severe HCM had a significantly higher NT-proBNP concentration compared to the other groups (P<0.0003), however, the sensitivity of NT-proBNP for diagnosing cats with severe disease was only 44% (cutoff≤100pmol/l) to 55% (cutoff≤40pmol/l). There was no significant difference in NT-proBNP concentration between normal, equivocal and moderate categories (sensitivity for detecting moderate HCM was 0%). Based on the results of this study, NT-proBNP concentration is not considered adequate as a screening test for detecting mild to moderate HCM in Maine Coon cats and it appears that it may miss many cats with severe HCM.

Natriuretic peptides: the feline experience

In feline medicine natriuretic peptides (NP), particularly NT-proBNP, have emerged as biomarkers with significant potential. Since the introduction of the commercial ELISA that enabled the convenient and accurate measurement of circulating N terminal ANP and BNP fragments research examining the utility of these peptides as an aid to the diagnosis of feline cardiovascular disease has accelerated. This article describes the results of these studies and tries to put them in the context of clinical practice by exploring the areas of agreement and controversy and explaining the influence of confounding factors on the interpretation of NP concentrations. Considerable further work is needed to fully evaluate the clinical utility of NP regarding their potential for diagnosis, prognosis, and guidance of treatment.

Feline myocardial disease 2: diagnosis, prognosis and clinical management

Clinical challenges The diagnosis, prognosis and clinical management of feline myocardial disease (cardiomyopathy, CM) represent controversial areas in veterinaty cardiology. Diagnosis is challenging primarily because of the complex classification of feline CM, which is based on a variety of structural and functional phenotypes. Similarly, prognosis is strongly dependent on the underlying aetiology and stage of the disease, which are often unrecognised. These challenges underline the importance of a thonaugh clinical evaluation of the patient and understanding of the underlying pathophysiological mechanisms in order to select the most appropriate treatment and provide the highest standards of care.

Patient group Although a genetic predisposition has been demonstrated in some feline pedigrees (ie, Maine Coons, Ragdolls), CM can potentially affect all breeds and different age groups.

Audience General practitioners, as well as specialists in small animal medicine, cardiology and pathology, deal with feline CM cases on a regular basis.

Diagnostics Diagnosis of feline CM is primarily based on echocardiographic examination. However, even the most sophisticated techniques present important limitations because they do not necessarily identify the primary cause of the disease or recognise the precise origin of an end-stage myocardial disease. Thoracic radiography remains one of the most useful tools for identifying changes consistent with congestive heart failure. Novel diagnostic techniques include cardiac magnetic resonance imaging, positron emission tomography and genetic tests.

Evidence base Although knowledge of feline CM remains fairly rudimentary, important discoveries have been made in the past few years. Evidence-based studies have significantly improved understanding of genetic predisposition, biomarkers and response to pharmacological treatments. Hopefully, many of the unsolved questions raised in this article will find a definitive answer in the near future.

Plasma concentrations of natriuretic peptides in normal cats and normotensive and hypertensive cats with chronic kidney disease

OBJECTIVES

To determine if natriuretic peptide concentrations are increased in cats with systemic hypertension and/or chronic kidney disease (CKD).

ANIMALS

22 normal cats, 13 normotensive cats with mild-moderate CKD (NT-CKD), 15 hypertensive cats with mild-moderate CKD (HT-CKD) and 8 normotensive cats with severe CKD (NT-CKD-severe).

METHODS

N-terminal pro-B-type (NT-proBNP) and pro-A-type (NT-proANP) natriuretic peptides were measured in plasma samples from all cats using commercially available assays and concentrations in the normal and diseased groups compared using non-parametric statistical tests. Spearman's rank correlation was used to test for an association between natriuretic peptide and creatinine concentrations.

RESULTS

NT-proANP was significantly higher in the NT-CKD-severe than the normal group of cats (P=0.006) but there were no other differences between groups. NT-proBNP concentrations were significantly higher in the HT-CKD group than both the normal (P<0.001) and the NT-CKD (P<0.001) groups. NT-proBNP concentrations were also higher in the NT-CKD-severe (P<0.001) and the NT-CKD (P=0.005) groups than the normal group. NT-proANP but not NT-proBNP was significantly and positively associated with plasma creatinine concentration.

CONCLUSIONS

Measurement of NT-proBNP shows promise as a diagnostic marker for systemic hypertension in the cat. Its concentration is not significantly increased in cats with mild-moderate normotensive CKD.

Assessment of the diagnostic accuracy of circulating natriuretic peptide concentrations to distinguish between cats with cardiac and non-cardiac causes of respiratory distress

OBJECTIVES

To determine if serum natriuretic peptide (NP) concentrations could distinguish cardiac from non-cardiac causes of respiratory distress (RD) in cats.

ANIMALS

Seventy-four cats from 1 university hospital were used.

METHODS

Serum NP concentrations were measured in 41 cats with non-cardiac respiratory distress (RD-NC) and compared to 33 cats with RD due to congestive heart failure (RD+CHF) using sandwich enzyme immunoassays (ELISA).

RESULTS

RD-NC cats had lower (P=0.0001) median NT-proANP and NT-proBNP concentrations (614 and 45 fmol/mL, respectively) than RD+CHF cats (1690 and 523 fmol/mL, respectively). The area under the curve was 0.88 and 0.96 for the receiver operating curve analysis of the diagnostic accuracy of NT-proANP and NT-proBNP concentrations to discriminate RD+CHF from RD-NC cats (P=0.036). An optimum cut-off concentration of 986 fmol/mL for NT-proANP and 220 fmol/mL for NT-proBNP accurately discriminated RD-NC from RC+CHF cats with a sensitivity of 93.8% and 93.9% and a specificity of 80.3% and 87.8%, respectively.

CONCLUSIONS

Serum NP concentrations were different in RD+CHF cats compared to RD-NC cats. Evaluation of circulating NP concentrations may be helpful in the initial approach to cats presenting with respiratory distress, particularly if advances in ELISA technology result in a rapid cage-side test.

Investigation into the use of plasma NT-proBNP concentration to screen for feline hypertrophic cardiomyopathy

OBJECTIVE

To evaluate the utility of feline NT-proBNP plasma concentration [NT-proBNP] as a screening tool for cats with subclinical hypertrophic cardiomyopathy (HCM).

ANIMALS, MATERIALS AND METHODS

Forty adult Maine Coon or Maine Coon crossbred cats from the feline HCM research colony at the University of California, Davis were studied. All cats had previously been genotyped as heterozygous or negative for the A31P myosin binding protein C (MYBPC) mutation. Echocardiograms were performed to assess the severity of HCM in each cat. Blood samples were collected for evaluation of [NT-proBNP].

RESULTS

In these cats with severe HCM, [NT-proBNP] was significantly elevated (P<0.0001) when compared to all other groups of cats and an [NT-proBNP]>44pmol/L accurately predicted the presence of severe HCM. However, [NT-proBNP] was not increased in cats with moderate or equivocal HCM when compared to normal cats. Cats heterozygous for the MYBPC mutation had a significantly elevated [NT-proBNP] when compared to cats without the A31P mutation (P=0.028).

CONCLUSIONS

Measurement of [NT-proBNP] has a high sensitivity and specificity as a means of detecting severe HCM in cats, but it is not sensitive for the identification of moderate HCM as judged by the evaluation of Maine Coon and Maine Coon cross cats in our colony. Consequently, we conclude that this test cannot be used to screen cats for the presence of mild to moderate HCM.

Measurement of N-terminal proatrial natriuretic peptide in plasma of cats with and without cardiomyopathy

OBJECTIVE

To determine whether plasma N-terminal proatrial natriuretic peptide (Nt-proANP) concentrations in cats with cardiomyopathy (CM) differ from values in healthy cats and evaluate whether plasma Nt-proANP concentrations can be used to discriminate cats with CM and congestive heart failure (CHF) from CM-affected cats without CHF.

ANIMALS

16 cats that had CM without CHF, 16 cats that had CM with CHF, and 11 healthy control cats.

PROCEDURES

All cats underwent a physical examination, assessment of clinicopathologic variables (including plasma thyroxine concentration), thoracic radiography, and echocardiography. On the basis of findings, cats were assigned to 1 of 3 groups (control cats, cats with CM and CHF, and cats with CM without CHF). Venous blood samples were obtained from all 43 cats, and plasma Nt-proANP concentrations were measured by use of a human proANP(1-98) ELISA.

RESULTS

Plasma Nt-proANP concentrations differed significantly among the 3 groups. Median Nt-proANP concentration was 381 fmol/mL (range, 52 to 450 fmol/mL), 763 fmol/mL (range, 167 to 2,386 fmol/mL), and 2,443 fmol/mL (range, 1,189 to 15,462 fmol/mL) in the control group, in cats with CM without CHF, and in cats with CM and CHF, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Measurement of plasma Nt-proANP concentration could be of benefit in the assessment of cats with naturally occurring CM and might have potential as a screening marker for the disease. Furthermore, measurement of plasma NtproANP concentration may be useful for distinguishing cats with CM and CHF from those with CM and no CHF.