References
A practical guide to heart murmurs for veterinary nurses
Abstract
Heart murmurs are a relatively common finding in small animal medicine, and are additional sounds to the normal ‘lub’ and ‘dub’ heard on auscultation. The most common type of murmur recorded is a systolic murmur, and can be an indicator of disease severity in dogs with mitral valve disease. However, murmur intensity is not related to the severity of dilated cardiomyopathy, and in cats, having a murmur has been linked to a favourable outcome, while cats can have heart disease and have no heart murmur. It would be ideal if there was a heart murmur chart that correlated heart murmur auscultated, heart disease severity and anaesthetic risk. Unfortunately, such a thing does not exist, and it is up to the veterinary professionals involved, to interpret what heart murmurs mean and know which breeds are at risk of cardiac disease and/or cardiac failure. This means that the nurse needs to not only monitor heart rate, rhythm, and pulse quality, but also respiratory rate and effort, oxygen saturation and systolic blood pressure carefully in those suspected of, or those diagnosed with, cardiac disease.
Understanding the relevance of heart murmurs is an important skill in veterinary practice. Hearing additional sounds above the normal ‘lub’ and ‘dub’ sounds raises questions as to whether heart disease is present, and if it is, how severe it is. When an owner is told their pet has a heart murmur, they usually want to know the prognosis for their pet, which can be difficult to predict. Alternatively, if anaesthesia or medical treatment is required, veterinary professionals need to know the risks associated with any treatment provided. Murmurs can be indicative of heart disease severity in dogs with mitral valve disease, but not in dogs with dilated cardiomyopathy. Murmur detection in cats is also an unreliable indicator of heart disease. For an accurate guide of cardiac function, an echocardiogram is still the gold standard diagnostic tool. However, it cannot remove all risks associated with anaesthesia or aggressive fluid therapy.
There are two normal heart sounds, the ‘lub’ sound known as S1, and the ‘dub’ sound, known as S2. S1 occurs when the atrioventricular valves close, and marks the start of systole. S2 occurs when the semilunar valves close, and marks the start of diastole. Any other sounds are described as additional heart sounds. These additional sounds are described by three separate features. The first is where they are heard the loudest, called the point of maximal intensity (PMI). Figures 1 and 2 show the PMI on the left and right side of the thorax in the dog. Table 1 lists the different PMI locations in the dog and cat.
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