Prevalence of Heart Disease
Cardiac disease is one of the most common disease states presented to
the veterinarian. It has been estimated that up to 15% of dogs presented
to a practice may show some signs of cardiac disease and this increases
to over 40% in dogs older than 7 years of age. Disease prevalence has
always been less clear in cats, but some studies now suggest that up to
15% of cats may have changes suggestive of cardiac disease on
echocardiography.
Cardiac Disease in Dogs
Degenerative or chronic valvular disease (CVD) is the most common cardiac disease in dogs. In addition, dilated
cardiomyopathy (DCM) is relatively common in some large-breed dogs. Dogs
with CVD can be asymptomatic but usually have a murmur detected on routine
physical examination. Dogs with DCM can also be asymptomatic and may or
may not have a murmur or arrhythmia on physical examination.
Alternatively, dogs with cardiac disease can present in congestive heart
failure with clinical signs including coughing, dyspnea, weakness,
exercise intolerance and collapse. The challenge is that the presence of
a murmur or other evidence of heart disease in a dog presenting with
clinical signs such as coughing and respiratory distress does not
invariably mean that the clinical signs are a result of its cardiac
disease. These signs may in fact be resulting from concurrent
respiratory disease in the face of stable
CVD or DCM. Introducing the measurement of cardiac biomarkers into the
diagnostic workup of these patients can help to determine the
significance of the cardiac disease and appropriate next steps.
Cardiac
Disease in Cats
The challenge in
cats with cardiac disease is somewhat different. Cardiomyopathies are
the most common cardiac diseases in cats. Cardiac disease often remains
clinically silent in cats until the disease process is well advanced.
There may be subtle clues on physical examination that cardiac disease
is present, such as a murmur or gallop rhythm, but the significance of
these is often unclear without an extensive workup including an
echocardiogram. Measuring cardiac biomarkers in cats will add valuable
information and allow decisions to be made about the most effective next
steps to evaluate feline patients. In addition, as with dogs, cardiac
biomarkers can be useful to determine if signs of respiratory distress
are likely the result of primary cardiac or respiratory disease.
What is the
Cardiopet proBNP Test?
The Cardiopet
proBNP Test measures the circulating levels of NTproBNP. B-type or brain
naturetic peptide (BNP) is a member of a family of hormones that are released by the
myocardium in response to increased stretch. The action of these
hormones is to counter mechanisms that promote volume expansion causing
myocardial stretch. The primary effect is to promote naturesis (sodium
and water loss); hence the name. Like many peptide hormones they are
produced as large inactive precursor molecules known as prohormones.
Upon release, the prohormone is cleaved into the active hormone (the
C-terminal portion of the molecule), and NTproBNP (an active N-terminal
portion of the molecule). The body has many systems for eliminating the
active BNP and thus controlling
its action. The half-life is therefore short (in the order of seconds),
making it labile and difficult to measure. Conversely the inactive NT
portion is not as labile, and thus, it is an easier molecule to measure.
Cardiopet ProBNP can therefore be used as a valuable cardiac biomarker
for evaluation of cardiac disease.
When Should I
Have Cardiopet proBNP Done on My Pet?
The answer to
this question varies by disease and by species. NTproBNP levels increase
as cardiac disease worsens. Studies have shown that
NTproBNP is useful in the following scenarios:
-
To identify dogs
with cardiac disease
Elevations in NTproBNP can be used to identify dogs with cardiac
disease with a sensitivity of 83% and a specificity of 91%.
-
To differentiate
heart disease from respiratory disease in both dogs and cats
A number of studies have been published to show that NTproBNP can be
used to evaluate patients with respiratory signs and correctly
identify the underlying cause as either cardiac or respiratory.
The sensitivity and specificity for the test are typically in the
80s or low 90s depending on the investigator, species and study
methodology. In cats, NTproBNP has been reported to have a 94%
sensitivity, 86% specificity, 91.4% positive predictive value and
90.5% negative predictive value for differentiating cardiac from
respiratory causes of dyspnea.
-
To identify cats
with occult cardiomyopathy
NTproBNP is very useful in detecting the presence of cardiac disease
in cats without overt clinical signs. The marker is
capable of doing this with a reported sensitivity of 90% and a
specificity of 85%. In one study, all cats with a marker level of
>99 pmol/L had echocardiographic evidence of cardiac disease.
Studies are underway to assess the utility of NTproBNP in dogs
with occult cardiomyopathy.
