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volume-depleted cats and in other nonhypertrophic states.
Some congenital diseases commonly present with characterisic murmur features: A left-to-right patent ductus arteriosus (PDA) most commonly produce a continuous murmur best heard over the left heart base in both systole and diastole. A ventricular septal defect (VSD) commonly produce a pronounced systolic murmur with PMI over the right thorax.
Although the majority of canine patients with heart disease have an audible murmur, it is important to remember that some cardiac diseases (such as pericardial diseases, dilated cardiomyopathy, restrictive cardiomyopathy, atrial septal defects (ASD), and right-to- left shunting PDA) do not necessarily produce blood flow turbulence and an audible murmur.
Non-pathological murmurs can occur in cats of any age. Kittens may have “innocent” physiological murmurs assumed to arise due to large stroke volumes relative to the size of their great vessels. These murmurs usually disappear by approximately 5 months of age. High- output diseases, such as hyperthyroidism and anemia caused by various disease processes, can also give rise to a systolic murmur due to increased stroke volume and/or decreased blood viscosity.
Mild dynamic right ventricular outflow tract obstruction (DRVOTO) is a common non-pathological cause of physiologic murmur in healthy cats in stressful situations; such as examination at a veterinary hospital. DRVOTO can often be detected as a parasternal systolic murmurs in excited cats. Color Doppler echocardiography of these cats demonstrates a localized, turbulent systolic jet located within the right ventricular (RV) outflow region, originating just cranial to the tricuspid valve. Spectral Doppler tracings of the turbulent jets demonstrates abnormally high peak velocity, late systolic flow acceleration, and marked variability with heart rate, which is commonly seen with dynamic obstructions. Frame-by-frame examination of 2-dimensional (2D) echocardiographic images reveales systolic narrowing
of the the proximal outflow region of the right ventricle. DRVOTO in cats is generally benign and does not appear to be associated with progressive pathology.
Often, murmurs caused by cardiomyopathy and those resulting from non-pathological causes in cats cannot be differentiated from each other by auscultation alone as there is an overlap between auscultatory characteristics. Non-pathological murmurs tend to be fairly quiet (grade 1/6-3/6), but it is often not possible to classify systolic grade 1-3 murmurs as clearly pathological or non- pathological. Systolic grade 4/6-6/6 murmurs indicates the presence of structural heart disease. Murmurs in cats do commonly change in intensity with stress/excitement or variation in heart rate. However, this may occur
An Urban Experience
with murmurs of both pathological or non-pathological causes. Identification of gallop sound or arrhythmia may add evidence to the possibility that the murmur is caused by a structural heart disease.
Additional diagnostic testing
Differentiation of causes of feline cardiac murmurs
is difficult by auscultation alone without additional diagnostic testing. Thoracic radiography or measurement of circulating cardiac biomarkers can be helpful for detection of advanced cardiac disease, but a specific cardiac disease cannot be established by these techniques. Echocardiography is considered the diagnostic test of choice for pinpointing the cause of a murmur. The cause of the murmur must be evaluated
to a degree that is appropriate for the patient, and acceptable to the veterinarian and client. Indications for further testing include: Detection of overt clinical signs that could be referable to cardiac disease, suspicion
of a pathological murmur on the basis of auscultatory features, presence of galloup sounds and/or arrhythmia, the cat’s intended use (such as a potential breeding purpose), whether an event (such as anesthesia)
that could increase the risk of CHF, arrhythmia, or thromboembolism is imminent, client concern, or
desire to be aware of the cause of the murmur, and associated prognosis and treatment options, in addition to availability, cost, and perceived value of diagnostic tests. The owner should be informed that the etiology
of an murmur cannot be fully established in all cats,
but lack of structural heart disease, when evaluated by echocardiography, indicates that the murmur is of a non- pathologic origin.
Suggested reading
1. Cote E, Edwards NJ, Ettinger SJ, Fuentes VL, MacDonald KA, Scansen BA, et al. Management of incidentally detected heart murmurs in dogs and cats. J Am Vet Med Assoc. 2015;246(10):1076-88.
2. Cote E, Manning AM, Emerson D, Laste NJ, Malakoff RL, Harpster NK. Assessment of the prevalence of heart murmurs in overtly healthy cats. J Am Vet Med Assoc. 2004;225(3):384-8.
3. Nakamura RK, Rishniw M, King MK, Sammarco CD. Prevalence of echocardiographic evidence of cardiac disease in apparently healthy cats with murmurs. J Feline Med Surg. 2011;13(4):266-71.
4. Rishniw M, Thomas WP. Dynamic right ventricular outflow obstruction: a new cause of systolic murmurs in cats. J Vet Intern Med. 2002;16(5):547-52.
5. Wagner T, Fuentes VL, Payne JR, McDermott N, Brodbelt D. Comparison of auscultatory and echocardiographic findings in healthy adult cats. J Vet Cardiol. 2010;12(3):171-82.

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