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Heart Murmur, Physiologic 413

Possible Complications PEARLS & CONSIDERATIONS the murmur’s cause (pathologic or nonpatho-
Overinterpretation or underinterpretation of Comments logic) without an echocardiogram.
VetBooks.ir to failure to provide an accurate treatment plan • 25%-69% of cats with heart murmurs have SUGGESTED READING Diseases and Disorders
incidentally detected heart murmurs can lead
no detectable heart disease.
and prognosis.
Côté E, et al: Management of incidentally-detected
indicated. The murmur is a clue, and the
Assoc 246:1076, 2015.
PROGNOSIS & OUTCOME • Treatment of a heart murmur is never heart murmurs in dogs and cats. J Am Vet Med
cause to which the clue is pointing may or
Because incidentally detected murmurs occur may not benefit from treatment. AUTHOR: Etienne Côté, DVM, DACVIM
EDITOR: Meg M. Sleeper, VMD, DACVIM
in animals without associated clinical signs,
the prognosis is often fair to good. Many Technician Tips
disorders are progressive, but some (notably Cats routinely have heart murmurs that are
patent ductus arteriosus) lend themselves to heart-rate dependent or that can vary in
being cured. The exact prognosis therefore intensity between anesthesia and being awake.
depends on establishing the underlying cause These characteristics are typical of physiologic
and its degree of severity. murmurs, but it is impossible to be certain of

Heart Murmur, Physiologic Client Education
Sheet

BASIC INFORMATION PHYSICAL EXAM FINDINGS relatively smaller left ventricular outflow
• These murmurs are more easily auscultated tract without other changes consistent
Definition over the left heart base, occur during systole, with SAS.
Heart murmurs not associated with cardiac and are usually soft (<III/VI). • Emotional stress also increases cardiac output
disease • Pale mucous membranes may be evident in and should be taken into consideration
patients with physiologic heart murmurs when auscultating and/or echoing these
Synonyms caused by anemia. patients.
Innocent murmurs, flow murmurs, nonpatho- • Fever may cause a physiologic murmur.
logic heart murmurs DIAGNOSIS
Etiology and Pathophysiology
Epidemiology • The genesis of a murmur is affected by Diagnostic Overview
SPECIES, AGE, SEX multiple factors; structural heart disease Physiologic heart murmurs cannot be diagnosed
Physiologic heart murmurs are common creates turbulence and/or increases blood solely by auscultation, and an echocardiogram
in puppies and kittens, and these generally velocity due to valvular leakage (regurgita- is necessary to rule out structural heart disease.
disappear by 4-6 months of age. Other causes tion), abnormal shunts, or obstructive lesions However, the echocardiogram may be delayed if
for murmurs unrelated to heart disease can be (p. 414). there is evidence supporting a cause for physi-
detected at any age. • Physiologic heart murmurs result from a rela- ologic murmur (e.g., if severe anemia exists,
tively high cardiac output. It is hypothesized echocardiogram may be postponed to see if
GENETICS, BREED PREDISPOSITION that young patients have a relatively high resolution of anemia results in resolution of
• Hound dogs (e.g., greyhound, Italian grey- stroke volume for their great vessels, causing murmur).
hounds, salukis) and, in general, athletic dog physiologic murmurs. As these patients grow,
breeds are particularly prone to developing their great vessels enlarge and the murmur Differential Diagnosis
physiologic heart murmurs. disappears, usually by 6 months of age. Other causes of heart murmurs: congenital
• Boxer dogs • Changes in blood properties, such as its (pulmonic or subaortic stenosis, ventricular
viscosity or density, can also lead to heart septal defects, atrioventricular valve stenosis),
RISK FACTORS murmurs in normal hearts. In patients with acquired (degenerative valvular disease, sec-
• Athleticism anemia, the combination of decreased blood ondary valvular regurgitation due to dilated,
• Anemia viscosity due to a low hematocrit and an hypertrophic, or restrictive cardiomyopathy,
• Other high cardiac output conditions increased stroke volume can result in a bacterial endocarditis).
(anxiety, hyperthyroidism, fever) physiologic murmur.
• Greyhounds and other athletic hunting dogs Initial Database
ASSOCIATED DISORDERS may have a soft, basilar systolic murmur that • Echocardiogram
Commonly associated with severe anemia is physiologic. An echocardiogram, which is • Hematocrit
necessary to rule out a pathologic cause for
Clinical Presentation the murmur, may demonstrate transaortic
HISTORY, CHIEF COMPLAINT velocities that are slightly increased but still TREATMENT
• Physiologic murmurs in puppies/kittens in the normal range and a normal cardiac Treatment Overview
or athletic dogs are found during routine structure. • No treatment is necessary for pediatric or
checkups. • Although boxer dogs are predisposed to athletic murmur.
• Patients with murmurs caused by anemia subaortic stenosis (SAS), these dogs also • Patients with physiologic murmurs due
or fever can show clinical signs associated have an increased prevalence of physiologic to anemia or fever need treatment for the
to these underlying conditions. murmurs that are thought to be due to a underlying systemic condition.

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