August 20, 2018

MVC 2018: Advances in Feline Heart Disease Diagnosis

Combining radiology, echocardiography, and cardiac stress marker results can bring clarity to ambiguous cases.
By Natalie Stilwell, DVM, MS, PhD
About half of cats with murmurs have diagnosable cardiac disease.

Cats are more adept than dogs at hiding clinical signs of heart disease, according to Rebecca Stepien, DVM, DACVIM, clinical professor of cardiology at the University of Wisconsin School of Veterinary Medicine. That’s why it is important to use multiple available diagnostic tools to detect and stage cardiac disease in cats. At the 2018 Midwest Veterinary Conference in Columbus, Ohio, Dr. Stepien presented the latest tools for diagnosis of cardiac abnormalities in cats. She began by emphasizing the importance of differentiating heart disease and heart failure in the feline patient.
 

Differentiating Heart Disease and Heart Failure 

Cardiac disease, she said, is typically monitored rather than clinically treated in cats, whereas cardiac failure is almost always treated. Heart disease is defined as a physical or functional abnormality of 1 or more components of the cardiovascular system; heart failure occurs when cardiac output provides inadequate blood pressure for organ perfusion despite normal hydration status. Cardiac failure may manifest clinically as hypotension due to low cardiac output or as congestion, edema, or other fluid accumulation due to sodium and/or water retention.

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Detecting asymptomatic heart disease in cats is not a straightforward process. Dr. Stepien estimated that approximately one-quarter to one-third of overtly healthy cats have heart murmurs. About half of cats with murmurs have diagnosable cardiac disease, while in the other half the murmurs are innocent. Dr. Stepien emphasized, “No murmur likely means no disease.” She added that the most common life stage for development of myocardial disease begins at about 6 to 8 years of age and decreases after 12 to 14 years.

Gallop Rhythm and Cardiac Arrhythmia
To determine whether a heart murmur is causing disease, Dr. Stepien advised examining for additional abnormal findings, especially a gallop heart sound or cardiac arrhythmia. Gallop heart sounds occur when rapid ventricular filling suddenly stops because of abnormal stiffness of the ventricular wall, thus generating a third heart sound. The condition, which may be temporary or permanent, can be caused by a variety of pathologies, including hypertrophic or dilated cardiomyopathy, ventricular fibrosis (eg, restrictive cardiomyopathy), and neoplasia. In particular, Dr. Stepien noted, feline lymphoma can infiltrate and stiffen the heart wall. Increased ventricular dilation leading to gallop heart sounds can also occur in patients with renal disease after receiving fluid therapy because of overhydration and increased blood volume. The combination of a cardiac murmur and an arrhythmia also increases the likelihood of true cardiac disease, she said.

Heart Murmur in a Healthy Cat: Should I Still Worry?
A heart murmur may warrant additional investigation even in patients with no outward clinical signs, Dr. Stepien noted. Further diagnostics should be performed before any cat with a murmur undergoes anesthesia or receives fluid therapy. Also, certain systemic diseases, such as occult hypertension, anemia, and hyperthyroidism, can exacerbate a murmur and should be ruled out. Finally, some clients may encourage further diagnostics for peace of mind.
 

Diagnostic Imaging for Cardiac Abnormalities

Dr. Stepien noted that radiology is more useful than echocardiography for assessing congestive heart failure, but echocardiography is needed to evaluate cardiac anatomy. Many cats with cardiac disease lack significant atrial and/or ventricular enlargement on radiographs but will show enlargement when imaged by echocardiography. Obese cats frequently deposit fat in the pericardium, thus enlarging the cardiac silhouette on radiography even in the absence of cardiac disease. In such cases, Dr. Stepien advised examining the pulmonary vessels as an additional indicator of cardiac disease. She also noted that if the heart touches the diaphragm, it is likely enlarged.

Another limitation of radiography is the large overlap in vertebral heart scores between normal and abnormal cats. According to 1 study, a vertebral heart score of 8 or higher is only 78% sensitive for detecting left heart disease with no or mild left atrial enlargement1; however, sensitivity increases to 91% if left atrial enlargement is mild to moderate. Study results showed that vertebral heart score was 82% specific for detecting left heart disease, regardless of left atrial size. Therefore, vertebral heart score may be an unreliable predictor of cardiac disease. Dr. Stepien emphasized the use of echocardiography, particularly for detecting preclinical heart disease in cats. An echocardiogram provides direct information on heart structure, such as wall thickness and chamber size, as well as function. In particular, Doppler echocardiography is valuable for assessing systolic and diastolic function. An echocardiogram can also identify pleural effusion, diaphragmatic hernia, and mass lesions and can differentiate between benign and disease-related causes of heart murmur and gallop heart sounds. In short, echocardiography is an incredibly useful tool to help rule in or out heart disease.

Echocardiography holds particular value for screening at-risk cat breeds, including the sphynx and Maine coon, for hypertrophic cardiomyopathy before breeding. As noted earlier, diagnostics such as echocardiography should be performed before administering anesthesia or fluid therapy in patients with heart murmurs. Echocardiography is also the most effective tool for detecting intracardiac thrombi.

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