An Engineer’s Guide to Basic Cardiology (Yours and Your Hound’s)
by Frances Abrams, PhD
How It Works
The heart is a pump. It takes blood from the body, sends it to the lungs, takes it back from the lungs and sends it to the body. Like most pumps, it has a controller, in this case a series of electric impulses from the nervous system. This controller manages the rhythm and the rate of the pump. When it is working properly the heart is said to be in sinus rhythm.
The pump also has a mechanical means of pushing fluids from one place to another (the muscles surrounding the chambers of the heart) and some holding chambers for transferring fluids (the chambers of the heart) with valves to control the direction of flow.
There is a phase in which the heart muscles are contracting and pushing blood out (systole) and a phase when the muscles are relaxing so that the pump can fill with blood (diastole). Muscles that are too weak or stretched will not be able to push as much blood through the heart. Also important to blood flow are the large sophisticated pipes, the connecting blood vessels, such as the aorta, leading in and out of the heart.
The heart, whether yours or your dogs, is a reliable well-tested design. However, like all pumps, it can fail. There may be “manufacturing defects” and parts will wear out. There is a limited warranty contained in the genome, influenced by the amount of work and abuse the heart sees. Fortunately, although we cannot yet order up spare parts, there are things we can do to detect and combat wear and tear on this important organ and to stretch its life past the warranty. With our breed, relatively few dogs have defects at birth (congenital). Most heart disease in the Irish Wolfhound is hereditary but develops over time (developmental) and commonly does not show up for 5 to 6 years.
A good thorough cardiac examination at age 2 or 3 provides a baseline with which to mark the original condition of your dog’s heart. Repeating the exam, or at least parts of it, on a regular basis allows early detection of changes to the heart and treatment to increase length and quality of life.
Measurement and monitoring
Since we cannot take the heart out of an animal for testing, we rely on indirect methods of determining how it is working. Each part of a cardiology exam provides a slightly different look at the overall system and, using them in combination, gives the complete picture of heart health. Knowing the systems that are most likely to fail is a real asset in this case. Each breed has a set of typical problems, and seeking out a cardiologist who has experience with your breed is valuable. Knowing the normal heart rate at home where he is relaxed is invaluable. (Also see the "Monitoring" paragraph in Bill Tyrrell’s article: Cardiac Health in Irish Wolfhounds for details.) An increase in heart rate is often the first sign of stress.
Auscultation is when your veterinarian uses a stethoscope to listen to the sounds the heart makes while working. Abnormal sounds (called murmurs) may indicate leaks or turbulence in the flow of fluids. Some murmurs are benign, but some may indicate a need for further investigation. Auscultation can also detect certain kinds of changes to the rhythm of the heart that may indicate an electrical problem. The advantage of auscultation is that the tool (stethoscope) is available to anyone and is relatively inexpensive. It is a totally non-invasive procedure that most dogs tolerate well.
However, some practitioners are more skilled at interpreting the sounds they hear and some have better hearing. Auscultation is an imprecise tool, especially in the hands of inexperienced practitioners and those of us who are simply tone deaf.
The familiar x-ray is a good tool for looking at the size and shape of the heart and for fluid build up around the heart. An x-ray is a static picture and best used in conjunction with other information. The dog must lie still, sometimes in an uncomfortable position and usually in an uncomfortable place. Radiographs can be stressful for the dog. Some veterinarians, on seeing an Irish Wolfhound heart for the first time, and knowing the tendency of the breed to cardiomyopathy, will assume that the heart is dilated just because it is so much larger than they are used to seeing.
Often shortened to “echo” by veterinarians and sometimes referred to as cardiac ultrasound, an echocardiogram is the gold standard of diagnostics in veterinary cardiology. Sound waves are directed into the body using a transducer, or probe. These sound waves then interact with the tissues in the body. Some of the sound waves are reflected back to the transducer. By analyzing these reflected sound waves, the ultrasound machine is able to create images of the heart that are then displayed on the monitor. This allows the cardiologist to see a picture of the heart muscle, the heart valves, the great arteries in action and to see the blood flowing through the heart. Key dimensions can be directly measured, including the volume of each contraction and can be compared to norms for the breed and age. Leakage and turbulence around valves can be detected, and this is a good way to check to see if a murmur is benign.
An echo is about the same as auscultation as far as the dog is concerned. Alcohol and ultrasound gel are applied to the fur on each side of the chest either with the dog in a standing position or lying on its side. The examiner moves the probe that is about the size of a screwdriver handle, around the chest and looks at the image on the screen, snapping stills at the peak of expansion (diastole) and contraction (systole) of the heart and looking at the heart chambers and major blood vessels.
An echo should be done by a board certified cardiologist, preferably one who has experience with Irish Wolfhounds. While the procedure may appear simple in concept, getting a good image depends on the orientation and location of the probe and the timing of measurements. You know your dog best but if it is easily upset by separation or sensitive to strangers it may do better if you can stay with it during the examination. An important thing to ask when you schedule the appointment is whether they do echoes standing or lying down (many wolfhounds are more comfortable standing). Ask the practice how many echoes they do and how often they see Irish Wolfhounds.
The EKG (electrocardiogram) is another non-invasive test. This is a test of the electrical system, however, rather than a picture of the heart. Four electrodes are attached to the four limbs of the dog, and a little alcohol or gel is added to get good conduction through the skin. Then the electrical potential between each combination of electrodes is measured for a period of time to get a tracing of the electrical signal over time. This also can be done either standing or lying on the side. It is usually easier to hold an Irish Wolfhound still when standing, as they feel comfortable in that position.
The EKG provides a quantitative measure of the length of time each part of the pump cycle is taking and also shows how well the “wiring” is working. If electrical pulses are not properly coordinated or come out of sequence, the heart may be beating but not providing good pumping action. While this is often visible during an echo, the EKG provides more information on why a heart may look uncoordinated. Sometimes these faults in the electrical system lead to the structural faults seen in echoes.
Electrical faults may be continuous or intermittent. In Irish Wolfhounds, by far, the most common continuous fault is atrial fibrillation. An intermittent fault that sometimes shows up is a ventricular premature contraction (VPC). The latter may not show up in the relatively brief recording (usually less than a minute) of an EKG. Under certain conditions, a cardiologist may suggest a longer recording or a 24-hour monitoring with a device called a Holter monitor.
The Holter monitor does require that small patches be shaved for the electrodes so that they can be firmly attached to the skin with adhesive. The dog is then fitted with electrodes, a harness and a recorder that continues recording the heart. The owner is given a diary or asked to take notes of the dog’s activities throughout the time the Holter is on the dog. There may be an event button on the recorder that the owner can push to signal specific occurrences or observations that they note in the diary.
Some laboratories offer blood tests that are good predictors of heart disease in some breeds. The Irish Wolfhound norms for these tests are yet to be established, but it is being researched. If proven to be accurate for our dogs, these tests could be less expensive than the cardiology exam and perhaps give an early indication of risk factors.
The Irish Wolfhound Foundation offers clinics at many national and regional club events. These clinics are also providing data for research, so the cardiologists on site are picked for their experience and interest in the breed. The owner is encouraged to be with the hound throughout the examination. Echo clinics at all-breed shows may also be excellent, if offered by a board certified cardiologist.