Page 77 - Feline Cardiology

Chapter 8: Cardiac Biomarkers 73

ramipril therapy in asymptomatic cats with HCM. In nostic evaluation (physical examination, echocardio-
this study, ramipril did not change left ventricular mass gram, etc.).
or improve diastolic function (and similarly no signifi- Clearance of natriuretic peptides in mammals is
cant change was noted in NT-proBNP levels) (MacDonald thought to occur renally. In cats with systemic hyperten-
et al. 2006). A large-scale, single-institution, prospective sion, since many have concurrent renal disease, interpre-
study evaluating NT-proBNP levels in 425 cats covering tation of NT-proBNP may be problematic. In a study
the full clinical spectrum (normal to end-stage heart that evaluated natriuretic peptides in cats with renal
failure) has demonstrated serum NT-proBNP level cor- disease, only NT-proANP correlated with creatinine Diagnostic Testing
relates with stage of cardiovascular disease severity as concentrations, with NT-proBNP performing better as
well as survival. This study also demonstrated that sex, a diagnostic test. However, although azotemia was not a
body weight, and blood pressure are not associated with confounding factor in the evaluation of NT-proBNP,
significant differences in circulating levels of NT- systemic hypertension, as mentioned above, was associ-
proBNP (Ettinger 2010). According to these findings, ated with an increase in NT-proBNP (Lalor et al. 2009).
feline NT-proBNP levels below 100 pmol/l indicate that Systemic hypertension likely stimulates increased pro-
significant cardiovascular disease is unlikely, whereas a duction of BNP secondary to elevated cardiac afterload.
level greater than 270 pmol/l indicates clinically signifi- Therefore, it is possible that elevated NT-proBNP levels
cant disease is highly likely. NT-proBNP levels between caused by systemic hypertension could be misinter-
100–270 pmol/l suggest an intermediate result where preted as indicative of primary cardiomyopathy if blood
cardiac disease can neither be ruled in nor ruled out pressure is not measured.
(Ettinger 2010). Several human studies suggest multiple biomarker
At this time there is one assay for NT-proBNP on the strategies are of greater value than using a single marker
market for veterinary use in the United States (Idexx alone. It is likely the same will be true in veterinary
Cardiopet™ proBNP test) and the blood sample must medicine. The search for new biomarkers for human
be shipped to the Idexx laboratory for analysis. Two patients is ongoing, and studies using the currently
studies focusing on clinical relevancy of the test have available ones will be essential to better define clinical
shown that NT-proBNP can distinguish between con- utility for these tests. The rapid development of this
gestive heart failure and noncardiac causes of acute field seen to date will probably continue for the foresee-
dyspnea in cats (Connolly et al. 2009; Fox et al. 2009). able future. The possibility exists that these assays will
See Table 8.1 for their suggested cutoff values. It is often be useful for prognosticating and optimizing medical
difficult to distinguish the underlying cause of dyspnea management of individual feline cases. Until results are
in cats, particularly when the cat’s severe respiratory rapidly available, they are unlikely to alter emergent care
distress limits diagnostic evaluation. These results in veterinary medicine and there is currently no evi-
suggest NT-proBNP levels will be a useful adjunctive dence they will be useful to screen asymptomatic cats
diagnostic in these critically ill cats, especially when a for underlying cardiomyopathy.
rapid, cage-side test is available. However, the test was
not useful for screening earlier stages of heart disease: REFERENCES
asymptomatic Maine coon or Maine coon crossbred cats
with mild or moderate HCM did not have elevated NT Boldface font indicates key references.
proBNP levels, suggesting it is unlikely the test will be Adams JE III, Schechtman KB, Landt Y, et al. Comparable detection
useful to screen clinically normal cats (Hsu et al. 2009). of acute myocardial infarction by creatine kinase MB isoenzyme
and cardiac troponin I. Clin Chem 1994;40:1291–1295.
The test does not replace a traditional, complete diag- Adin DB, Milner RJ, Berger KD, et al. Cardiac troponin I concnetra-
tions in normal dogs and cats using a beside analyzer. J Vet Cardiol
2005;7:27–32.
Table 8.1. Proposed feline circulating plasma NT-proBNP cutoff Adin DB, Oyama MA, Sleeper MM, Milner RJ. Comparison of canine
concentrations for discriminating cats with dyspnea caused by cardiac troponin I concentrations as determined by 3 analyzers. J
Vet Intern Med 2006;20:1136–1142.
heart disease vs respiratory disease
Apple FS. Clinical and analytical standardization issues confronting
cardiac troponin I. Clin Chem 1999;45:18–20.
Study Plasma NT- Sensitivity Specificity
Bodor GS, Porterfield D, Voss EM, Smith S, Apple FS. Cardiac
proBNP (pmol/l) (%) (%)
troponin-I is not expressed in fetal and healthy or diseased adult
human skeletal muscle tissue. Clin Chem 1995;41:1710–1715.
Fox et al. 2009 265 90.2 87.9 Boswood A. Biomarkers in cardiovascular disease: Beyond natri-
Connolly et al. 220 93.9 87.8 uretic peptides. J of Vet Cardiol 2009;11:S23–S32.
2009 Braunwald E. Biomarkers in heart failure. N Engl J Med
2008;358:2148–2159.