Many purchasers, however, would be less familiar with the concept of performing more in-depth examinations for cardiac murmurs or arrhythmias detected during a routine PPE. The reason for this is difficult to determine, however, it may stem from the fact that many horses with cardiac murmurs detected on a routine examination do go on to perform without issue. Horses have a large heart with a relatively slow heart rate and therefore physiologic murmurs and some arrhythmias are common and occur without any underlying cardiac injury. Any turbulence in blood flow as the blood moves through the chambers and out through the large blood vessels (aorta and pulmonary arteries) can be detected as a murmur. By careful auscultation and identifying the location of the murmur and characterising the type and intensity, a veterinarian can identify physiologic murmurs and be confident to eliminate them as a course of future concern. However, when heart murmurs are not physiologic, prognosticating on their clinical importance and their potential to negatively affect performance is fraught with danger unless a full cardiac workup is performed.
One of the findings from this study was that relying on the horse’s breed, sex and age, together with assessing the heart with a stethoscope alone, were not always a reliable predictor of a horse’s future performance. The best predictor of whether a cardiac abnormality would affect future performance, put the rider or horse at risk, or shorten the lifespan of the horse, was to do a comprehensive cardiac examination.
An echocardiogram is currently the best diagnostic tool available to assess a heart murmur. This is an ultrasound assessment of the heart that allows direct visualisation of the functioning heart. During this procedure, the size of the atrial and ventricular chambers, as well as the size of the large blood vessels, can be assessed and measured, the valves between chambers can be examined, and the flow of blood through the heart can be followed.
Although most veterinarians do have an ultrasound machine in their cars, electrocardiography requires a dedicated program to interpret images and a small probe that can fit between the ribs to examine the heart, and is different to the ultrasound probes used for rectal or tendon scans. There are three types of modes used when assessing the heart:
- B-mode (2D) to look at the spatial arrangement, similar to how we look at tendons and other structures
- M-mode to assess the heart and chamber sizes when the heart is pumping (structures are in motion)
- Doppler to assess blood flow through the chambers and valves
Together these allow the veterinarian to look for thickenings in the heart wall, increased sizes of heart chambers, and disruptions to normal blood flow through the heart valves that can indicate pathology in the heart.