We’ve already discussed a bit about the types of heart disease that are common in dogs and cats, but how do we go about diagnosing and treating heart disease?
Diagnosis starts in the consulting room, when we are listening to the heart with a stethoscope. This is a cornerstone of the physical examination of your pet. Auscultation may disclose an abnormal heart sound (a murmur) or and abnormal rhythm. Listening carefully to the sound and location of the murmur gives us important clues about what is going on. However, a stethoscope doesn’t tell us about the size of the heart or the health of surrounding vessels and lung tissue.
Radiographs, or x-rays of the chest, allow us to see the silhouette of the heart and measure it. This is done most accurately by comparing it to the size of the bones of the spine, giving us a measurement called the vertebral heart score. An increased vertebral heart score shows that the heart is enlarged, which can indicate that it is time to start medication to support the function of the heart.
The benefit of chest x-rays is that they allow us to look other structures in the chest cavity – for example the lungs and airways. Airway disease can be another cause of clinical signs such as a cough, that might be due to heart disease. An early sign of congestive heart failure is fluid accumulation in lung tissue, which can be seen on x-rays. The disadvantage of chest x-rays is that the animal needs to be sedated or anaesthetised to take them. In some animals, particularly cats, with trouble breathing this can be very risky.
An ECG measures the electrical impulses that occur as the heart beats. It is used mostly to diagnose and assess a cardiac arrhythmia – an abnormal heart rhythm. This is important in selecting the correct treatment to normalise the rhythm. Some arrhythmias only occur intermittently. In those cases, the animal may wear a portable ECG monitor for 24 hours or more to be able to record the arrhythmia when it occurs.
An echocardiogram is the examination of the heart with an ultrasound scanner. This can give us a lot more information about the size of the heart overall, as well as the size of the individual chambers of the heart. The ultrasound scanner can also be used to look for tumours around the heart, abnormal accumulations of fluid in the pericardial sac that surrounds the heart, and problems with blood flow within the heart that might predispose to a blood clot forming. We can also look at the heart beating in real time and measure its strength, which is important in diagnosing some conditions such as dilated cardiomyopathy.
In most patients, an echo can be performed without sedation (and should be where possible, as many sedatives affect the function of the heart and may alter the scan results). In many ways, it gives us much more information than a chest x-ray, though it does have the disadvantage that we cannot make assessments of lung tissue or airways.
Heart muscle that is damaged or stretched will secrete certain substances into the bloodstream in predictable quantities. By taking a small blood sample, we can measure these, and they can be a useful way of getting an idea if there may be cardiac enlargement. While they are not as accurate as a chest x-ray or scan, they are very quick and stress free to obtain, and can be a useful early screening test in animals that may be at risk of heart disease, or for monitoring the progress of heart disease in an individual animal. The most useful of these in animals measures a substance known as pro-BNP.
The type of treatment prescribed to a pet with heart disease will depend on the type of heart disease they have. Some of the most common medications used include:
These are used to decrease fluid accumulation in the lungs that occurs secondary to heart disease. Though they don’t do anything to correct the underlying cause, for many pets they are very important in improving their quality of life and reducing the clinical signs associated with congestive heart failure.
Pimobendan works by slightly slowing down the heart, and increasing the strength of the heartbeat. This helps to improve cardiac function in a large number of conditions. A recent large scale study into the impact of pimobendan on dogs with a murmur due to mitral valve disease has showed that by starting medication when the heart begins to enlarge we can delay the onset of congestive heart failure by an average of 15 months. For affected dogs this means another 15 months of symptom free time, so this is a real improvement in their life expectancy and quality of life.
This is the name given to a class of medications that block the action of an enzyme within the animal’s body – known as angiotensin converting enzyme. The effects of this medication act to reduce the workload of the damaged heart, allowing it to function more effectively. They are used to treat heart disease in dogs, but not generally cats (though they are used in the treatment of kidney disease in cats, due to other beneficial effects they have).
These three medications form the mainstay of treatment of heart disease in dogs and cats. Some medications are used less commonly, such as anti-arrhythmic medications to correct abnormal heart rhythms, or anti-clotting medication such as clopidogrel which may be used in cats to lower the risk of a blood clot forming within the weakened heart. None unfortunately are able to reverse the damage to the heart itself, but can act to help a pet with heart disease live a normal life for years to come.