Page 151 - Feline Cardiology

150 Section D: Cardiomyopathies

and 83%, respectively) (Hsu et al. 2009). Elevated and typically by also performing an echocardiogram
plasma [BNP] does not define the type of heart disease and an electrocardiogram.
present, nor the presence or absence of secondary cardiac
changes such as atrial enlargement or SAM of the mitral Endothelin I
valve. Elevated plasma [BNP] is also not specific for Endothelin 1 (ET-1) is a potent vasoconstrictor that also
heart disease, since some normal cats have an elevated exerts other deleterious effects including cardiomyocyte
plasma NT-proBNP, but raises the suspicion that heart hypertrophy and activation of cardiac fibroblasts. ET-1
disease may be present. A substantial degree of overlap levels are increased in people with heart failure, and they
in plasma levels exists between normal and mildly increase with severity of heart failure. Increased ET-1
abnormal cats, and a plasma NT-proBNP measurement was associated with a higher 1-year mortality in people
Cardiomyopathies evaluation, nor as a stand-alone screening test for HCM plasma ET-1 levels in cats with various cardiomyopa-
with chronic heart failure. Only one study has evaluated
cannot be considered a substitute for a complete cardiac
thies; most had HCM (Prosek et al. 2004). ET-1 was
in the cat.
Other pertinent areas of future research need to
increased in asymptomatic cats with cardiomyopathy
explore the utility of NT-proBNP for monitoring disease
(11/12 cats had HCM) compared to normal cats, and in
progression, guidance of pharmacologic therapy, and
potential use as a prognostic indicator as it is in humans. cats with heart failure compared to normal cats, but was
not different between asymptomatic cats and symptom-
NT-proANP appears to be less useful than NT-proBNP atic cats. No cut-off values or sensitivity and specificity
for detection of HCM in asymptomatic cats, as plasma calculations were made. There appeared to be consider-
levels are not elevated in cats with HCM compared to able overlap in ET-1 concentrations between individual
control cats (MacLean et al. 2006). cats in the normal group and the asymptomatic cardio-
myopathy group. Given the lack of ability to distinguish
asymptomatic cardiomyopathic cats from cats with
Cardiac troponin I heart failure or arterial thromboembolism, it is likely
Cardiac troponin I (cTnI) is released from cardiomyo- that other biomarkers such as NT-proBNP are more
cytes when they are damaged. Unlike ANP and BNP, clinically useful than ET-1 in cats.
cardiac troponins are not species-specific; the molecular
structure is the same across mammalian species. Cardiac Other Laboratory Tests
troponins are entirely distinct from skeletal troponins, Serum growth hormone
and therefore skeletal muscle injury or inflammation
does not cross-react with cTnI tests. Cardiac troponin-I
appears to be the more sensitive test (providing greater
accuracy), compared to the cTn-T test that preceded its Key Points
development. Serum cardiac troponin I (cTnI) has been
studied in cats with cardiomyopathy and heart failure, • Serum growth hormone levels may be mildly increased
and it has been shown to be a sensitive biomarker for in cats with HCM, but they are much higher in cats with
heart disease in cats (sensitivity 87%, specificity 84%) acromegaly. The increase in growth hormone in HCM is
but did not distinguish cats that were symptomatic from not likely a primary factor in development of concentric
ventricular hypertrophy.
asymptomatic cats (Connolly et al. 2003). Another study • Serum insulin like growth factor-1 ± growth hormone
found contradictory results, with increased cTnI in levels should be measured in cats with concentric
asymptomatic cats with cardiomyopathy, and that was hypertrophy of the left ventricle and clinical
further increased in symptomatic cats with heart failure abnormalities suggestive of acromegaly.
(Herndon et al. 2002). Normal reference ranges are not
interchangeable between the different cTnI sandwich
assays, because the five commercially available cTnI Growth hormone exerts an endocrine effect on the heart
assays evaluate five different areas of the molecule using by inducing cardiomyocyte growth, which leads to con-
proprietary technology. Therefore, when interpreting a centric ventricular hypertrophy in people and cats with
cTn-I result in any species, the reference range for the acromegaly. Growth hormone also increases calcium
instrument used in the analysis must be provided. A sensitivity of the cardiac myofilaments and increases
positive cTnI value obligates the clinician to identify calcium content within cardiomyocytes, which increases
potential cardiac disease by reviewing the history for contractility. Given the known relationship of growth
potential trauma or illness leading to myocarditis and hormone and insulinlike growth factor-I to hypertrophic
the history of heart disease in the individual or family, cardiac remodeling, serum growth hormone was mea-