Page 150 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 149

sis in response to increased ventricular wall stress or other correlated to left ventricular mass index in another study
neurohormonal stimulation such as endothelin 1 (Yasue (Mizuno et al. 2000). It is likely that stimuli such as
et al. 1994; Biondo et al. 2003). Atrial natriuretic peptide neurohormones (angiotensin II and ET-1), in addition
(ANP or A-type) is synthesized in the atria in response to to hypertrophy, induce BNP synthesis in patients with
volume overload and increased wall stretch, but BNP HCM. [BNP], but not [ANP], is highly correlated with
appears to have a greater diagnostic potential than ANP degree of LV ventricular outflow tract obstruction, which
given its greater degree of elevation in cardiac disease and is understandable given that BNP secretion is partially
congestive heart failure in cats (Sisson 2004). In people load dependent (Hasegawa et al. 1993). To no surprise,
with HCM, there is increased ventricular BNP and ANP plasma concentrations of both natriuretic peptides are
content in regions of myocardial fibrosis, hypertrophy, higher in people with HCM and evidence of diastolic
and myocyte disarray (Hasegawa et al. 1993). Amino dysfunction on Doppler echocardiography compared to
terminal pro-brain natriuretic peptide (NT-ProBNP) normal individuals (Ogino et al. 2004). Similarly, [BNP]
offers the most promise of all neurohormonal biomark- and [ANP] are moderately correlated with LV end- Cardiomyopathies
ers for detection of heart failure in cats, and likely for diastolic pressure in patients with HCM (r = 0.69 and
detection of heart disease in cats (see Chapter 8). r = 0.51, respectively), which is a reflection of the sever-
Atrial and brain natriuretic peptides have similar bio- ity of diastolic dysfunction (Mizuno et al. 2000). In
logic effects of diuresis, natriuresis, selective dilation of patients with asymptomatic HCM but without SAM,
the afferent renal arterioles with subsequent increased measurement of [BNP] but not [ANP] is predictive of
glomerular filtration rate, and vasodilation leading to exercise-induced myocardial ischemia (Nakamura et al.
reduction in pulmonary capillary pressure, mean right 2002).
atrial pressure, systemic and pulmonary vascular resis- The undeniable appeal of cardiac biomarkers is the
tance, pulmonary artery pressure, and increased cardiac potential to assess the heart using a blood sample and
index and coronary blood flow (Mills et al. 1999). detect various degrees of heart disease and heart failure.
Natriuretic peptides also inhibit release of renin and The only commercially available (Cardiocare by IDEXX
endothelin I, causing secondary decreases in angiotensin Laboratories) and clinically applicable assay in cats is a
II and aldosterone (Nakao et al. 1992). Ancillary proper- rapid sandwich ELISA to measure the inactive fragment
ties of ANP and BNP include antifibrotic and antihyper- amino-terminal ProBNP (NT-ProBNP). The principal
trophic effects in the renal mesangial cells, cardiac application of NT-proBNP testing is the differentiation
fibroblasts, cardiomyocytes, and endothelial cells. of congestive heart failure from noncardiogenic disor-
Plasma brain natriuretic peptide concentration ders (i.e., primary respiratory disease) in cats with acute
([BNP]) is a sensitive biomarker for cardiac disease and dyspnea. Initial data appear very promising for screen-
heart failure in people and in animals. [BNP] is elevated ing for heart failure, but its use for screening asymptom-
in both systolic and diastolic dysfunction, and it is atic cats with cardiac disease is less clear because there
further elevated proportional to the severity of heart are variable results and lower sensitivity. NT-proBNP
failure in people. Plasma [ANP] is moderately elevated has a longer circulating half-life than BNP, which may
and [BNP] is markedly elevated in people with HCM increase its sensitivity for detection of heart disease or
(Mizuno et al. 2000; Briguori et al. 2001). Although ini- failure. NT-proBNP is useful to discriminate between
tially thought to be released only from atrial stretch, it heart failure and primary respiratory disease in cats,
is now known that ANP is synthesized in the ventricles with a high sensitivity of 90% and a specificity of 86–
of people with heart failure and asymptomatic people 88%. It also may be useful to screen for cardiac disease
with HCM (Ogino et al. 2004). Increased plasma [ANP] in asymptomatic cats, but the sensitivity is likely less
and [BNP] are due to increased LV synthesis in people than when screening for heart failure. In a small pilot
with HCM and are correlated with diastolic dysfunction study of 23 asymptomatic cats with various cardiomy-
but not with left atrial dimension (Ogino et al. 2004). opathies (mostly HCM), NT-proBNP was highly sensi-
Although higher than normal, plasma [BNP] in patients tive (88%) and specific (100%) for detection of heart
with HCM was fourfold less than patients with idio- disease (Fox et al. 2008). Oppositely, NT-proBNP was
pathic dilated cardiomyopathy (DCM) (94 pg/ml versus not elevated, using the same assay as the study afore-
418 pg/ml, respectively) in one study (Mizuno et al. mentioned, in any asymptomatic Maine coon cat with
2000). A possible explanation for the much greater mild to moderate HCM (n = 21) compared to normal
degree of BNP elevation in DCM is that there is greater cats (n = 9), but was elevated in asymptomatic cats with
wall stress in DCM when compared to HCM. [ANP] and severe HCM (n = 10) compared to normal cats, mildly
[BNP] were minimally correlated to LV mass in one affected cats, or moderately affected cats, with a high
study (r = 0.36 and r = 0.32, respectively), and were not sensitivity and specificity for diagnosis of HCM (90%