Dr Brigite Pedro
VVS Cardiology Specialist
Have you heard a heart murmur during a clinical exam of a puppy or a kitten? When you detect a murmur in these young patients it can be concerning for owners; Dr Brigite Pedro shares her guidance for what to do next.
A heart murmur is always concerning for an owner, particularly if this is detected in a new puppy or kitten. It is therefore important to know how to manage these situations in the best way.
First of all, it is important to understand that not all murmurs are due to underlying structural heart disease. Murmurs can be pathological or non-pathological. Non-pathological heart murmurs can be functional (when there is a physiological explanation for the murmur – for example a significant anaemia) or innocent (when no obvious physiological or anatomical reason for the murmur is detected). On the other hand, pathological murmurs are caused by underlying structural heart disease (e.g. an abnormal valve or septal defect), which should be identified as soon as possible.
Typically, the first health check takes place at 6 weeks of age. At this young age, most of these puppies and kittens will still be with the breeder. If a heart murmur is detected at that time, further investigations should be recommended before they go to a new home (or at least, the new owner should be informed that the puppy or kitten they are buying has a heart murmur).
The most common congenital cardiac defects in puppies are patent ductus arteriosus (PDA), pulmonic stenosis and subaortic stenosis. Identifying these conditions as soon as possible is essential to provide the best care. In the case of a PDA for example, early diagnosis can make the difference between the dog having a normal life expectancy or going into heart failure before they reach adulthood.
Luckily, not all puppies with a heart murmur will have congenital heart disease that requires intervention. In fact, approximately 25% of puppies younger than 4 months will have an innocent murmur. It is therefore important to examine these patients in detail to decide what the best course of action is.
The decision between recommending additional investigations as soon as possible or just monitoring the murmur with a repeat auscultation a few months later, should be based on the characteristics of the murmur (loudness, location, and timing within the cardiac cycle) and on the rest of the physical examination. If clinical signs are present or if any other cardiovascular abnormalities are detected, further tests should always be recommended.
Nonpathological heart murmurs can be intermittent, they tend to be systolic, of short duration, usually soft (grade 1-2 /6) and with a point of maximum intensity over the base of the heart. Typically, a murmur with these characteristics will most likely be an innocent or a functional murmur (caused by an extra-cardiac condition, like anemia or fever), although echocardiography (cardiac ultrasound) would be needed to confirm this. Nevertheless, as a rule, these soft intermittent murmurs do not warrant immediate investigations if the pet is asymptomatic. If the murmur persists over time, further investigations should then be recommended. Obviously, it is important to have a detailed discussion with the owners and if they are worried about the murmur (and many will be!) an echocardiography can always be recommended to put their mind at rest. It is also important to understand what the purpose of the puppy is (for example, if the puppy is intended for breeding purposes, breeding should not happen until after an echocardiographic evaluation is performed).
On the other hand, pathological heart murmurs are consistently and readily audible, they can be systolic, diastolic, or continuous, they tend to be loud (grade 3/6 or louder) and may radiate widely from the point of maximum intensity. Sometimes they are accompanied by other changes on physical examination (for example a gallop sound, an arrhythmia, or a change in peripheral pulse quality. These murmurs should always be investigated with a complete Doppler echocardiographic examination. Some complementary diagnostic tests can be considered, for example ECG, biomarker measurement or thoracic radiographs, however these tests tend to be non-specific, and an echo will always be required for a definitive diagnosis of congenital heart disease.
Echocardiography in young puppies tends to be technically challenging, due to the small patient size and the complexity of some congenital cardiac defects. It requires a good understanding of cardiovascular anatomy and physiology, especially if more than one congenital defect is identified, which is relatively common. Therefore, ideally the echocardiographic examination should be performed by a Specialist in Veterinary Cardiology (or if performed by a less experienced vet, they should have support from a Cardiology Specialist to aid with image acquisition and interpretation). Some of these young patients may also require sedation to enable a diagnostic cardiac scan.
The most common congenital cardiac defects in kittens are ventricular septal defects, pulmonic and aortic stenosis, patent ductus arteriosus and mitral or tricuspid dysplasia. However, some conditions that typically affect adult cats, for example hypertrophic cardiomyopathy, can occur at any age and therefore should also be considered in young cats with heart murmurs.
Nonpathological murmurs in kittens can be innocent or functional, but they can also be iatrogenic (for example due to excitement and a fast heart rate, or even because of the external pressure that is put on their soft compliant chest wall with the stethoscope during cardiac auscultation). These murmurs tend to be soft (rarely > 2/6) and systolic, with variable intensity and heard best over the left base or left apex.
However, in the absence of obvious extra-cardiac conditions that could cause a physiological murmur (for example pale mucous membranes due to a severe anemia), these soft systolic murmurs can also be pathological. The only way to be certain of the origin of the murmur is by performing echocardiography. Alternatively, repeating the auscultation a few weeks later can also be considered and further investigations can then be performed if the murmur persists. If this murmur is detected in a cat that will require a general anesthetic or that is going to be used for breeding purposes, echocardiography should be recommended to fully assess its origin.
On the other hand, if a loud systolic or continuous murmur is noted, or if a gallop sound or arrhythmia are evident, echocardiography is definitely recommended, as a pathological murmur is more likely. Other diagnostic tests such as thoracic radiographs can be considered, however they will provide less detailed cardiac information.
Like with puppies, echocardiography should ideally be performed by a Specialist in Veterinary Cardiology (or at least by someone with experience in echocardiography, supported by a Cardiology Specialist). Due to their small size and the complexity of some of their congenital cardiac defects, the echocardiographic examination can be challenging, and some of these young patients may require sedation to enable a diagnostic cardiac scan.