All of us would be worried if we are told at the first vaccinations that our puppy has a murmur. A murmur could represent a serious congenital heart defect – (congenital means a defect the puppy is born with). The chances depend on the breed of the pup and the loudness of the murmur. To put things into perspective, the incidence of congenital heart disease is about 7 cases per 1000 puppies, so the chances that your puppy is affected are slim.
A murmur represents turbulent blood flow through the heart. This is usually the result of high velocity flow caused by either blood flowing through a narrowing under pressure or the leakage of one of the main valves within the heart. Murmurs are scored out of 6 with 1 being the quietest, audible after listening carefully for a few minutes in a quiet room. Grade 6 murmurs are audible with the stethoscope lifted off the chest!
Almost all puppies with congenital heart disease have a murmur and the louder the murmur, the more serious the problem. If we can feel a vibration or “thrill”, on the side of the chest wall representing grade 5 or 6, then there is likely to be significant disease and further investigation is needed.
Some murmurs have a characteristic sound and the majority occur when the heart is contracting, during systole. If the murmur is continuous, then the likely diagnosis is a congenital heart defect called patent ductus arteriosus (PDA). This is one of the three most common congenital heart defects in dogs. The other two involve narrowing or “stenosis” at the base of the main aorta (from the left ventricle) or pulmonary artery (from the right ventricle).
Indecision often exists about the significance of a murmur at a young age because we also see innocent flow murmurs in puppies. These are murmurs that have no underlying disease and get quieter as the puppy grows. They have often disappeared by maturity.
Unfortunately, some breeds that are prone to congenital heart diseases such as the Boxer also commonly have innocent flow murmurs as puppies. Innocent flow murmurs are usually quieter and have soft blowing character. Indeed about 50% of all boxer puppies have detectable murmurs. This does not mean that they will need treatment for heart disease as many are innocent flow murmurs or mild sub-aortic stenosis. The significance may also depend on the future of the dog. Mild sub-aortic stenosis that would not affect a pet would be catastrophic for the breeding potential of a dog. Unfortunately it is usually impossible to differentiate between an innocent flow murmur and mild to moderate sub-aortic stenosis without further investigations, such as echocardiography (heart scan).
If the murmur persists and further evaluation is required, a non-invasive technique using ultrasound can confirm the diagnosis and give guidelines regarding severity. This can usually be performed with the puppy lying on its side being gently restrained. Sedation is rarely required although we usually have to shave a small patch of fur behind the elbow on the chest wall.Full Article >