The Heart
Diagnostic Tools

Author: Wendy Wallner DVM Whirlwind Boxers

Chest X-rays
show the size of the cardiac silhouette which may or may not be the same size as the heart itself. (Certain conditions that cause a build up of fluid around the heart could make the heart appear larger than it actually is.) Usually the silhouette is equal to the size of the heart so that chest X-rays give us an impression of heart size. We can also see the diameter of the trachea (windpiipe) and the bronchi, the blood vessels in the lungs, whether the lungs are clear or have some sort of infiltrate (fluid, pus, blood, etc.) and whether the infiltrate appears to be in the alveoli (air sacs) of the lungs or in the spaces between. We can sometimes see evidence of a mass (like a tumor) in the lungs or on the heart. For evaluating heart disease, these are not very accurate since enlargement of the heart usually comes later in heart disease after symptoms have begun.

is a measurement of the electrical activity of the heart. When leads from the ECG machine are attached to different areas of the animal the electrical impulses are measured across those leads (one is a positive electrode and one negative). When an electrical impulse from the heart moves toward the positive lead, there is a positive (upward) blip made on the ECG screen or paper, while an impulse moving away from the positive lead produces the negative blip. The ECG can be valuable in diagnosing arrythmias if they are occurring continuously or with very high frequency (several per minute). If the arrythmias are sporadic, they are of use only if the arrythmia is occurring at the time of the exam. It is true that significant cardiac disease may be present and produce minor or NO abnormalities on ECG. The ECG does not show how the heart is functioning mechanically, only how the electrical impulses are occurring.

are made by use of Ultrasound equipment. The echo does allow one to see the mechanical function of the heart. You can see the heart contracting, the valves opening and closing and how they move, whether there are any irregularities (vegetative growths) on the valves. You can measure the chamber diameters when the heart is contracting and when it is relaxed. You can measure the thickness of the muscular walls of the chambers. Doppler echocardiography adds a sound component to the above and allows one to hear the turbulence that is known as a heart murmur in an amplified mode.

Color-flow doppler
also adds color to the image and allows visualization of blood flow through the heart and major vessels.

The Holter Monitor
is a backpack type recording device that enables a prolonged sampling of an ECG. This piece of equipment is the most useful in detecting intermittant arrythmias due to the long sample time (24 hours or longer). Since most cases of boxer cardiomyopathy begin in the early phase as a minor arrythmia, this is the most useful piece of equipment we have available currently to "screen" boxers for arrythmias.

Event recorder.
This is a device that can be worn for prolonged periods of time and activated only if the patient has an episode. It is a continuous loop type recorder, so that when activated by the push of a button, it saves the ECG pattern for the last several minutes. This would be useful for a dog that is having fainting spells (syncope) but who has normal ECGs when examined at the veterinary office. The owner would be instructed to push the activation button when the animal had the next episode. One could then determine if the cause of fainting was of cardiac origin (like an arrythmia).