Download Cardiac Biomarkers

The following article appeared in the DX Consult, No. 2, Vol. 1,
2008, published by IDEXX Laboratories.
CASE S TUDY
Cardiac Biomarkers
The value of NTproBNP
Andrew W. Beardow, BVM&S, MRCVS, DACVIM (Cardiology)
Disease Focus Initiative Manager, IDEXX Laboratories
Tabor
Patient: Tabor, 6-year-old, neutered male
domestic shorthair cat
Presenting complaints: Tabor presented
for his annual wellness check and vaccine.
History: No prior abnormalities were
reported. Diet included commercial dry
and canned products.
Physical examination
Tabor was bright, alert, responsive and hydrated. Mucous
membrane color and capillary refill time were normal. Thoracic
auscultation revealed a grade 2/6 systolic heart murmur with point
of maximal intensity at the left heart base. Respiratory rate was
normal. Lung auscultation was unremarkable. Heart rate varied
between 160 and 210 beats per minute. Weight was 11 lb.
The remainder of physical examination was within normal limits.
Assessment
Differential diagnoses for Tabor’s heart murmur included a benign
flow-related murmur, cardiomyopathy and congenital heart disease.
Diagnostic plan
CBC, complete chemistry profile and T4, and thoracic radiographs
were performed.
Laboratory findings
CBC, chemistry profile and T4 results were within normal limits.
Thoracic radiographs: Thoracic radiographs revealed equivocal
generalized cardiomegaly, but the pulmonary vasculature and lung
field were all within normal limits.
Additional testing: A blood sample to assess plasma
NTproBNP concentration was drawn and sent for evaluation
at the reference laboratory.
A follow-up appointment was scheduled to measure Tabor’s
blood pressure upon arrival prior to any other procedures. An
echocardiogram would be performed during that visit as well.
Plasma NTproBNP concentration result: The result was
135 pmol/L. This value is elevated and is consistent with cardiac
disease. Therefore, Tabor’s veterinarian was confident that an
echocardiogram was indicated to evaluate the etiology of Tabor’s
cardiac disease.
Several recent studies have shown that concentrations of
NTproBNP differ between healthy control cats, asymptomatic
cats with heart disease and cats with congestive heart failure.1,2
Therefore, this test can be clinically useful as an initial screening
test for cats with suspected cardiac disease. In addition, this test
can help to differentiate respiratory from cardiac causes of dyspnea
in symptomatic cats.3,4
Blood pressure: Tabor’s blood pressure was measured by Doppler
sphygmomanometry and determined to be normal (150 mmHg
based on an average of five recordings in a quiet room).
Echocardiogram findings: Figures 1– 3 show left ventricular
hypertrophy. (This is not the optimal view for making quantitative
measurements, but wall thickness was 6.5 mm as measured on a
short axis m-mode view.) There was evidence of asymmetric
hypertrophy of the septum; dynamic left ventricular outflow tract
obstruction (systolic anterior motion [SAM] of the anterior mitral
valve leaflet was present) and associated mitral valve insufficiency
were also documented.
Figures 2 and 3 show a portion of the mitral valve causing dynamic
obstruction of the left ventricular outflow tract. This obstruction
causes turbulent flow in the left ventricular outflow tract, which
contributes to the heart murmur. Displacement of the mitral
valve causes secondary incompetence and, consequently, mitral
regurgitation. Left atrial enlargement was also seen.
Final diagnosis
This was a fairly typical presentation for a cat with hypertrophic
obstructive cardiomyopathy (HCOM). The obstructive component,
confirmed by the presence of SAM of the mitral valve, is common
to the disease (reported to be present in >60% of cases). A heart
murmur is often detected incidentally during physical examination.
In this case, the elevation of the NTproBNP concentration
supported the presence of heart disease, which was documented
and characterized by follow-up echocardiographic examination.
Management recommendations
Treatment of asymptomatic cardiomyopathy in cats is controversial
and to date there is no consensus on management. Currently, there
is no evidence to support that therapy delays the progression of
disease or the onset of clinical signs, or that it improves outcome.
Some cardiologists would not recommend treatment while others
might advocate treatment. Owing to the presence of dynamic left
ventricular outflow tract obstruction, a beta-blocker such as atenol
could be administered once to twice daily and titrated to achieve
a resting heart rate between 160–180 beats per minute. A calcium
channel blocker could be considered because of the significant left
ventricular hypertrophy. An angiotensin-converting enzyme (ACE1)
inhibitor could be considered because of the enlarged left atrium. A
combination of an ACE1 inhibitor with a calcium channel blocker or
beta-blocker might be used by some cardiologists.
Left ventricular
outflow tract
Left ventricle
Mitral valve
Left atrium
Figure 1. 2-D long-axis view showing thickening of the left ventricular free wall
(line) and asymmetric septal hypertrophy (arrow) in diastole.
Recheck intervals are subjective. If a beta-blocker were administered,
then it would be reasonable to recheck the cat in 1–2 weeks to assess
heart rate and titrate the dose accordingly. Many cardiologists would
repeat an echocardiogram in 6 –12 months. Chest radiographs would
be indicated if the cat were to develop clinical signs of congestive
heart failure (e.g., tachypnea, dyspnea, coughing or syncope).
Currently, the value of monitoring sequential NTproBNP
concentrations is under investigation. Additional studies are needed
to determine if rising NTproBNP concentrations correlate with
disease progression or if stabilization or reduction in NTproBNP
concentrations occur with successful management.
Although management of Tabor’s cardiac disease is not
straightforward, obtaining a definitive diagnosis cannot be
undervalued. Tabor’s owners are now aware that he has a cardiac
disease. They can be instructed to monitor him more closely for signs
suggestive that he might be developing congestive heart failure (e.g.,
development of increased respiratory rate, dyspnea, cough, exercise
intolerance or lethargy). If clinical signs develop, then Tabor’s owners
will know that they should seek veterinary attention immediately. |DX|
Left ventricular
outflow tract
Left atrium
Figure 2. 2-D long-axis view showing a systolic frame capture. A portion of the
mitral valve is seen being drawn into the left ventricular outflow tract (arrow). This
causes turbulent flow in the outflow tract. Displacement of the mitral valve will
cause a secondary leakage. Both of these changes may be associated with
an audible murmur.
Left ventricular
outflow tract
Reference
1.Connolly DJ, Soares Magalhaes RJ, Syme HM, Boswood A, Fuentes VL, Chu L,
Metcalf M. Circulating natriuretic peptides in cats with heart disease. J Vet Intern Med.
2008;22:96–105.
Left atrium
MR
2.Fox PR, Oyama MA, MacDonald K, Reynolds CA. Assessment of NTproBNP
concentration in asymptomatic cats with cardiomyopathy [ACVIM Abstract 191].
J Vet Intern Med. 2008;22:759.
3.Wess G, Daisenberger P, Hirschberger J. The utility of NT-proBNP to differentiate
cardiac and respiratory causes of dyspnea in cats [ACVIM Abstract 28].
J Vet Intern Med. 2008;22:707.
4.Fox PR, Oyama MA, MacDonald K, Reynolds CA. Comparison of NTproBNP
concentration in cats with acute dyspnea from cardiac or respiratory disease
[ACVIM Abstract 65]. J Vet Intern Med. 2008;22:719.
Figure 3. 2-D long-axis view showing a systolic frame capture. In this image, the
color flow Doppler signal is shown. We see turbulent flow in the left ventricular
outflow tract (characterized by the speckled color pattern). A jet of mitral
regurgitation (MR) is also seen, probably the result of the displacement of the
mitral valve.
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