Importance of Echocardiogram Follow-up for positive ProBNP Results in Felines

2 case examples

Patient Information:

Patient 1
Age: 9 years Gender: Neutered Male
Breed: DSH Species: Feline

Patient 2
Age: 9 years Gender: Spayed Female
Breed: DSH Species: Feline

History:

Littermates/housemates presented for routine dental procedure. Snap ProBNP was performed as part of a pre-anesthetic laboratory panel. Abnormal results were obtained for both patients. Neither patient was displaying any clinical signs of heart disease and no murmurs or arrhythmias were present on exam. Echocardiogram was recommended.

Ultrasonographic Findings:

Patient 1
52 images including 2D, M-mode, color flow and Doppler imaging are available for review. The left ventricular wall is asymmetrically hypertrophied, especially the free wall with regions of remodeling and irregularity (IVSd 4.2, LVPWd 7.5, normal under 6 mm). There is a diffusely hyperechoic endocardium consistent with fibrosis. The systolic function is decreased (fractional shortening 31%, normal over 35%). The E and A waves are summated making assessment of diastolic dysfunction difficult. The papillary muscles are mildly remodeled. The left atrium is severely dilated (LA:Ao 2.64, normal under 1.6; LA diameter 28.6 mm, normal under 16). Spontaneous echo contrast visible but no obvious thrombus. Mild central MR due to annular stretch. Moderator band in LV lumen.

The right ventricle is also affected, with diffuse fibrosis and remodeling. Mild RA dilation with mild TR. Blood flow through the RVOT and LVOT is low normal velocity. Trace pulmonic regurgitation. No pericardial or pleural effusion. No obvious cardiac tumors.

LA:AO short axis view of Patient 1 demonstrating severe left atrial dilatation

“Smoke” (spontaneous echo contrast) noted in the left auricle in an optimized view for this area in Patient 1.

M-Mode left ventricle short axis of Patient 1 demonstrating increased thickness of the left ventricular posterior free wall in diastole.

Patient 2
41 2D, M-mode, color flow and Doppler images are available for review. The left ventricular wall is normal in dimension (IVSd 4.7, LVPWd 3.8, normal under 6 mm). There is a diffusely hyperechoic endocardium consistent with age-related fibrosis. Minimal remodeling. The papillary muscles are hyperechoic. The left atrium is normal in size (LA:Ao 1.34, normal under 1.6; long axis 13.3 mm). Systolic function appears adequate (fractional shortening 52%).

The right atrium is normal in size. The right ventricle appears normal. The mitral valve is normal in structure and mobility with no mitral regurgitation. The tricuspid valve appears normal in structure and mobility with trace tricuspid regurgitation. Blood flow through both the LVOT and RVOT are normal in velocity. Trace pulmonic regurgitation is identified.

LA: AO short axis view of the Patient 2 demonstrating a normal ratio.

M-mode left ventricle short axis of Patient 2 demonstrating normal ventricular wall thickness in diastole.

Echocardiogram Interpretation:

Patient 1
The finding of severe atrial enlargement in the face of moderate LV wall hypertrophy and systolic dysfunction is most consistent with hypertrophic cardiomyopathy developing a restrictive phenotype, however some historical infectious or inflammatory insult to the myocardium cannot be definitively ruled out. According to the most recent classification this is called non-specific cardiomyopathy. The biatrial dilation is causing insufficiency of both AV valves, and systolic dysfunction has developed.

Patient 2
No significant abnormalities noted. Trace tricuspid and pulmonic regurgitation.

Recommendations:

Patient 1
In view of the severe atrial enlargement, this patient is at high risk for thromboembolic events regardless of medications and this should be expressed to the owner (monitor for neurologic change, acute paralysis/lameness, etc).

Monitoring of sleeping breathing rates at home is highly recommended as the best way to screen for development of congestive heart failure at home.

Oral medications which are required lifelong:
Antithrombotic medication clopidogrel (Plavix) 75 mg tablets; give ¼ tab orally once daily (NOTE: this medication is very bitter on the cut edges so placing in a gel capsule can help).
Pimobendan (off label use) although starting this could be delayed until heart failure develops: 625 mg PO q12h.

A recheck echocardiogram is recommended in 6 months to assess for progression.

Patient 2
Given these findings, no medications are indicated. It is important to note that phenotypic HCM can develop at any phase of life in cats (particularly in this predisposed breed), and often does not accompany a heart murmur or physical examination abnormalities. Periodic screening is ideally recommended in all cats.

No cardiac contraindication for general anesthesia at this time.
Recommend recheck echocardiogram in 1 year to assess for development of disease, sooner if a murmur/gallop or clinical signs develop in the interim.

Discussion:

These two cases illustrate why performing screening echocardiograms on patients with abnormal proBNP results is so important. These patients are littermates and reside in the same household. Both are asymptomatic with no heart murmurs or other abnormalities on physical exam; however, their heart structure is drastically different. The male patient (Patient 1) has significant cardiac disease and is at high risk of thromboembolic disease, while the female patient (Patient 2) is basically normal. Assumptions cannot be made based on proBNP findings alone until further testing (ideally echocardiogram) is performed. This is illustrated nicely in this particular pair. ProBNP testing has been evaluated in multiple studies and is generally accepted as a useful “screening” modality in felines especially prior to anesthesia since occult cardiomyopathy can be common in this species. Negative test results have generally been accepted as reliable for ruling out significant cardiac disease. However, a recent paper did show a higher false negative rate when screening healthy cat populations than previously reported, so it is important to remember that a negative result does not definitively rule out heart disease. Furthermore, false positives can also occur and are often complicated by comorbidities common in geriatric felines such as renal failure or hypertension. It is also unclear if proBNP testing can detect cardiac disease prior to echocardiographic changes, so serial echocardiograms could also be considered in patients with abnormal proBNP results even if echocardiographic changes are not presently noted.

Sonographer: Kara Woody, DVM

Reference: Lu, et al. Point of Care N Terminal Pro-B type natriuretic peptide assay to screen apparently healthy cats for cardiac disease in the general practice.. J Vet Intern Med. 2021;35:1663–1672

Thank you to Dumfries Animal Hospital for collaborating with us on these interesting cases and Simon Swift, MA, VetMB, CertSAC, DipECVIM-CA (Cardiology), MRCVS for cardiology interpretation and comments on proBNP testing.