The KY Murmur Newsletter - October 2018

 

 By: Kristin Jacobs, DVM, Diplomate, ACVIM (Cardiology)

 

 The use of NT-proBNP has become an important part of veterinary cardiology.  NT-proBNP can be used as a screening test for cardiac disease in asymptomatic patients and in dyspneic patients to help determine if the cause of the symptoms are cardiac or respiratory.  Using these tests varies in different scenarios and varies among the different tests available.  While in human medicine, NT-proBNP can be used to guide treatment in patients with congestive heart failure, that information is not available in veterinary medicine at this time.

 

What is BNP/NT-proBNP?

• A biomarker measured in blood
• Produced by the ventricle in response to tension (either increased pressure or volume)
• Released as proBNP and then cleaved to active C-terminal BNP and inactive metabolite NT-proBNP
• NT-proBNP is more stable and more accurately measured than BNP and the most recent generation of the NTproBNP test measure metabolites of NTproBNP that are more stable in serum than the previously measured hormones  - no longer need special tubes!
• Diuretic, natriuretic, vasodilator, inhibits the Renin Angiotensin Aldosterone System
• Released early in course of heart disease
• Levels in blood correlate to severity of heart disease
• Test is species specific

Uses of NT-proBNP in Cats

Heart disease in cats is often silent.  In multiple studies, ~ 30% of cats with arterial thromboembolism (ATE) have no previous evidence of heart disease and no auscultable abnormalities at time of the ATE. Fifteen percent of apparently healthy cats have echocardiographic left ventricular hypertrophy.  It has become clear that auscultation alone is not enough to screen for heart disease in cats. Also, using NT-proBNP in addition to history and physical examination, improves practitioner confidence in radiograph interpretation.

When to use NT-proBNP in cats?

• Screening for HCM
• < 8 years of age, consider NT-proBNP every 2-3 years
• > 8 years of age, consider NT-proBNP as part of senior wellness profile
• Prior to anesthesia
• Consider in all cats 2 years of age or older, especially with abnormal auscultation
• NT-proBNP is preferred
• Truly normal cats have an NT-proBNP < 60 pmol/L (higher than this, should cause some concern with regards to anesthesia)
• Prefer NT-proBNP when possible, especially in asymptomatic cats. SNAP BNP may be used - interpretation is different.

Cardiopet BNP	SNAP BNP	Interpretation
<100 pmol/L	Negative	Clinically significant heart disease unlikely. Echo could be recommended.
>100 pmol/L	Abnormal	Increased risk of heart disease. Echo strongly recommended.

 

Cats with Respiratory Signs or Pleural Effusion

Cardiopet BNP	SNAP BNP	Interpretation
<100 pmol/L	Negative	Not supportive of CHF
100-270 pmol/L	Abnormal	CHF possible but patient may have occult CM with respiratory disease.
>270 pmol/L	Abnormal	CHF likely but still possibility of occult C with respiratory disease.

Take Home Points

SNAP BNP testing

• Abnormal test result - will see color change at ~ 150 pmol/L
• Screening - Strongest value is if test is Abnormal
• Some occult CM will be negative on SNAP BNP (see differences in cut-off values of Cardiopet BNP vs. SNAP BNP)
• Respiratory Signs - Strongest value is if test is Normal/Negative - where you have likely ruled out possibility of CHF
• Some cats with respiratory signs will be abnormal on SNAP BNP but have occult CM not CHF due to the difference in the cut-off

Remember: NT-proBNP can be increased by other diseases - most commonly in the cat: hyperthyroidism, severe renal disease and hypertension.

Uses of NT-proBNP in Dogs 

Dilated Cardiomyopathy (DCM) is often silent/occult and radiographic cardiac enlargement is difficult to detect, especially with early disease.  NT-proBNP can be used for screening for DCM in Doberman pinschers. The accuracy of using NT-proBNP as a screening test is improved to 91% when combined with Holter monitoring. It is important to note that levels of NT-proBNP in Dobermans with occult DCM are lower than the normal range for other breeds of dogs.

In contrast, degenerative mitral valve disease (DMVD) is the most common heart disease in dogs and is easily detected by a mitral murmur on physical examination.  Also, radiographic heart enlargement is relatively easy to detect.  There is evidence that NT-proBNP can be used in conjunction with echocardiography to predict the first onset of CHF

Screening for Heart Disease

	NTproBNP Level	Interpretation	Recommendation
Dogs with murmur and breeds at risk for DCM	NTproBNP < 900	Clinically significant heart disease likely.	Echo could be recommended.
	NTproBNP > 900	Clinically significant heart disease likely.	Recommend CVCA consult, consider thoracic radiographs if fluids or surgery indicated.
Doberman	NTproBNP > 735	Increased risk for occult DCM.	Recommend CVCA consult. Recommend thoracic radiographs if fluids or surgery indicated.
Dogs < 20 kg with murmur consistent with MVD	NTproBNP > 1,500	Increased risk for patient to present in CHF within next 12 months.	Strongly encourage CVCA consult. Recommend thoracic radiographs in the event fluids or surgery indicated.

 

In contrast, As in cats, NT-proBNP can be used to help evaluate if respiratory signs are due to CHF vs. other (ie: respiratory disease, neoplasia, etc.). There is no SNAP BNP test available for dogs.  

Dogs with Respiratory Signs

NTproBNP Level	Interpretation	Recommendation
NTproBNP < 900	Unlikely that clinical signs are secondary to CHF.	Consider further respiratory diagnostics.
NTproBNP 900-1,800	Indicates presence of significant heart disease, but equivocal for CHF.	Further diagnostics recommended to determine heart failure vs. other disease. Recommend CVCA consult.
NTproBNP >1,800	Indicates presence of significant heart disease with likelihood that signs are secondary to CHF.  Severe pulmonary hypertension (PHT) also a strong differential.	Recommend thoracic radiographs and treat supportively. If not responding appropriately, reevaluate for possible PHT. Recommend CVCA consult.

 

**** Some of the highest NT-proBNP values can be seen in patients with Pulmonary Hypertension - an elevated NT-proBNP means an echocardiogram is recommended, especially if not responding to CHF management ****

Remember - NT-proBNP can be increased by other diseases - most commonly in the dog: severe renal disease, pulmonary hypertension, Cushing’s disease, systemic hypertension.

See last page for Works Cited Sections for “Clinical Uses of NT-proBNP” 

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