This is the third of four articles focusing on heart problems in our pets. Having learned what signs you may see at home and what your vet will look for in an examination of your pet, we move on to the diagnostic tests that are commonly used and what they can tell us.
If the clinical signs and examination do not make it clear as to whether the problem is primarily caused by the heart, or a murmur is picked up but no clinical signs show, a blood test may be suggested. This will help to localise the problem to the heart and can be useful in picking up early heart disease (and differentiate it from an incidental, non-significant, murmur), which allows a full work-up, and if necessary treatment. Measuring the blood pressure, especially in cats, can also be useful in determining whether a heart problem is related to another issue such as an overactive thyroid.
One of the first steps in a cardiac work-up is likely to involve X-rays of the chest. Care is taken when sedating animals to get them to lie appropriately for X-rays to ensure the heart is not put under too much strain. However, it’s worth remembering that the stress of trying to achieve X-rays conscious (without sedation) can be as damaging to an animal and good quality X-rays are needed to help with an accurate diagnosis. An X-ray image comes out a bit like a black-and-white photograph. It shows gas and air density as black, bone density as white and everything in-between as grey. In order to get 3-D perspective, it is usual to take at least two X-rays at right angles to each other (one from the side and one looking down). The combined images give an idea of not only the size of the heart but also its shape, which is visible as grey silhouette against the air in the lungs. Changes in the heart’s shape are important because how the silhouette is distorted correlates with which individual chambers of the heart or blood vessels are enlarged.
Another way of looking at the heart is by ultrasound. This has the advantage of being possible conscious and can give information about the moving heart including, among other things, the thickness of chamber walls and valves, the speed and direction of blood flow and, when used in conjunction with an ECG, the strength of the heart muscle.
Finally, an ECG (electrocardiogram) is often done. Electrodes are used to record graphically the electrical activity of the heart over a period of time. It is used to show the rate and rhythm of the heart, as well as giving information about enlargement or imbalances of the body’s electrolytes. Again ECGs are normally carried out conscious but can be limited by only providing a snapshot of what is occurring at that point, not necessarily when an incident such as fainting is occurring. To remedy this problem, ECGs in a little kind of rucksack can be left on an animal for a prolonged period and the data recorded.
Used alone, each method is helpful but, to get a more complete and accurate picture of what is happening in the heart, and how far the disease has progressed, a combined approach is recommended, which may involve referral to a cardiology specialist who has all the appropriate equipment and expertise to interpret it.
Next week we complete the chapter on heart problems in pets by briefly discussing a few of the most common issues.