What should we advise to owners of clinically healthy pets, when we detect a cardiac murmur at a routine veterinary health check? Important differences between young, adult and geriatric animals, and between dogs and cats, as well as between various dog breeds will be emphasized.

Cardiac auscultation is one of the cheapest and least invasive screening test that practicing veterinarians use on a daily basis to look for congenital or acquired structural cardiac diseases. Detecting a cardiac murmur may have a major importance, but it can also be a clinically not relevant coincidental finding. The etiology of murmurs is very much different in young animals (puppies and kittens), compared to adult and geriatric cats, adult small-breed dogs and adult large-breed dogs.

Murmurs in Puppies and Kittens

Cardiac auscultation is part of a routine health check at the time of the first veterinary visit at the age of 6 weeks to look for congenital cardiac anomalies. The reason why we want to diagnose congenital cardiac anomalies is to protect the interest of the breeders, the new owners, the breed and the affected individual animal. Veterinarians help breeders so that no pets with a silent congenital cardiac anomaly would be sold to a new owner. Most congenital cardiac anomalies cause a murmur. On the other hand, up to 20% of clinically healthy puppies at the age of 7 weeks have an innocent cardiac murmur. Auscultation characteristics are specific and experienced veterinarians can differentiate innocent from pathologic murmurs.

Innocent murmurs are always soft (1–2/6), systolic and have a musical character (resembling the noise of a flying mosquito). When a louder systolic murmur is heard (especially with a palpable thrill) or the murmur has a diastolic component, the murmur is pathologic. Puppies with such pathologic murmurs should ideally be referred to a veterinary cardiologist for a Doppler echocardiographic examination without any delay. Most puppies and kittens with congenital cardiac anomalies grow well and show no clinical signs of a cardiac disease at all. This does not mean the cardiac condition is not severe. Exceptions are young animals with right-to-left shunting anomalies (such as tetralogy of Fallot) or the presence of congestive heart failure; these animals do not grow well and often typically have exercise intolerance. Several congenital cardiac anomalies can be treated well (such as patent ductus arteriosus, dynamic aortic stenosis and pulmonic stenosis) if diagnosed early enough. The most common cardiac anomalies that lead to a murmur are patent ductus arteriosus, aortic stenosis, pulmonic stenosis, ventricular septal defect, mitral or tricuspid valve regurgitation by dysplasia. A combination of these anomalies may also be present. Some congenital anomalies cause no or only a very soft murmur, such as atrial septal defect or mitral stenosis. Therefore, the absence of an audible murmur does not rule out the presence of a congenital cardiac anomaly.

Murmurs in Adult Cats

Cardiac murmur in adult asymptomatic cats is common. The murmur is mostly a soft systolic murmur and is best heard on either side of the sternum. The reason for cardiac murmur in adult cats can be a cardiac disorder, but it could also be an innocent murmur, or a systemic disease (such as anemia or hyperthyroidism). The most common anomaly in adult cats that causes a murmur is systolic anterior motion of the septal mitral valve (SAM), which leads to a mitral regurgitation and a dynamic left ventricular outflow tract obstruction. Other possible causes are dynamic right ventricular outflow tract obstruction (DRVOTO), intraventricular obstruction or pulmonary hypertension. The most common feline cardiac disorder, the hypertrophic cardiomyopathy does not cause a murmur. The only way to find out what the cause of a murmur is a Doppler echocardiographic examination. Because feline cardiac disorders are very challenging, this examination should ideally be performed by a board-certified veterinary cardiologist, just like it is recommended in young animals.

Murmurs in Geriatric Cats

The same causes as listed in adult cats should also be considered in cats above 10 years of age. In addition, systemic hypertension and hyperthyroidism should be excluded in any cat above the age of 8 years, even if they are clinically healthy and show no signs of these disorders. These diseases are very common and if diagnosed early enough can be treated. Timely intervention in cases of systemic hypertension (of any cause) and hyperthyroidism can prevent the development of congestive heart failure.

Murmurs in Adult Small-Breed Dogs

Murmurs in this population are most of the time systolic and the point of maximal intensity is the left cardiac apex. These murmurs are usually caused by a mitral valve regurgitation as a result of myxomatous valve degeneration. In a middle-aged to elderly (older than 6 years) asymptomatic dog of a predisposed breed (such as small terrier breeds, Cavalier King Charles spaniel, dachshund), cardiac auscultation is usually sufficient to diagnose the disease, as other disorders leading to such a murmur are extremely unlikely (such as dilated cardiomyopathy, bacterial endocarditis, SAM or congenital mitral dysplasia). If the murmur is different (like systolic and diastolic, or the point of maximal intensity is on the right hemithorax), Doppler echocardiography is essential to find its cause.

Murmurs in Adult Large-Breed Dogs

In asymptomatic adult large-breed dogs, mitral valve regurgitation can be caused by myxomatous valve degeneration and dilated cardiomyopathy. An echocardiogram is recommended to differentiate between these conditions.

References

1.  Szatmári V, van Leeuwen MW, Teske E. Innocent cardiac murmur in puppies: prevalence, correlation with hematocrit, and auscultation characteristics. J Vet Intern Med. 2015;29:1524–1528.

2.  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;13:266–271

3.  Paige CF, Abbott JA, Elvinger F, Pyle RL. Prevalence of cardiomyopathy in apparently healthy cats. J Am Vet Med Assoc. 2009;234:1398–1403.

4.  http://ejcap.fecava.org/en/ejcap-online-262-summer-2016-english/s03---heart-murmurs-in-pups-when-should-i-be-worried.html

5.  Boswood A, et al. Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: The EPIC study - A randomized clinical trial. J Vet Intern Med. In press.