Reprinted with the author's permission

Courtesy of DOGWORLD, 1990

It would be difficult to single out any one organ as more important to the body than any other, for there are many organs whose failure would be incompatible with life. The brain, lungs, kidneys and liver, in particular, are essential to life and, in the event of failure, there is very little one can do to replace their function. The heart, in a sense, is central to all of these organs, pumping blood filled with oxygen and nutrients to their cells, and carrying away metabolic wastes so that they don't become toxic. Consider, for a moment, just how remarkable this organ really is! No bigger than a small apple in the average size dog, it beats from 70 to 180 times per minute - depending on the size and age of the dog - propelling several times its total body weight in blood through a maze of arteries and veins each day. Yet, when stripped down to its bare essentials, the heart is really nothing more than a simple pump, regulated by modified and highly specialized nervous tissue.

Anatomically, the heart consists of four chambers - two atria (auricles) and two ventricles - with valves that close when the heart contracts and open as the heart
muscle relaxes, thus assuring that blood flows in only one direction. These four independent structures are so perfectly coordinated that the two atria beat in unison, followed a split second later by the two ventricles. Dark, venous blood containing carbon dioxide and metabolic wastes enter the right atrium, which contracts and forces the blood into the right ventricle. The right ventricle then contracts, sending the spent blood through the lungs, where the carbon dioxide is exhaled out of the body and exchanged for oxygen. Fresh oxygenated blood is now carried from the lungs to the left atrium which, as it contracts, forces it through the valve separating the two chambers and into the left ventricle. This, in turn, contracts a split second later, sending the fresh oxygenated blood into the arteries to be distributed to all of the cells of the body. As the blood passes through the kidneys and liver, impurities, metabolic wastes and toxic substances are either converted into harmless compounds or eliminated from the body.

CLASSIFICATION OF HEART DISEASE

Although there are many ways to classify heart disease, it is convenient to broadly divide it into either congenital or acquired disease. Acquired can then be further classified into diseases that affect either the heart's rate or rhythm, or the normal flow of blood through and out of the heart. These will be dealt with in more detail in a subsequent article.

DIAGNOSTIC PROCEDURES

Any good veterinary clinician can accurately diagnose most heart problems. What is equally important, however, is for every clinician to know his limitations, and
know when to seek help from someone with more specialized knowledge. We shall also see that it is not necessary to have a lot of very expensive diagnostic
equipment, as most diagnoses can be made with nothing more than a highly developed sense of touch and hearing. Before he does anything else, the good clinician will observe the dog's attitude and demeanor in the examination room. He will look for evidence of labored or abnormal breathing, as well as the way the fore legs are positioned while standing or sitting. If abnormalities are observed, these can often suggest the presence of fluids, tumors or other dense masses in the chest encroaching on the heart or lungs. After placing the dog on the examination table, the veterinarian can then check the jugular vein to see if it either pulsates, or is fuller than normal. He then place his hands over various parts of the chest to see if there are abnormal "thrills" or sensations radiating from the heart. Feeling and evaluating the pulse will not only tell him the heart rate, it can also give some indication of the condition of the circulation, as well. A good estimate of the amount of oxygen the blood is carrying can be made by looking at the tongue and mucous membranes of the lips. These should normally be bright pink, except in certain breeds such as the Chow. If they are dark blue, or purplish (cyanotic), it usually indicates that the heart is too weak to adequately pump blood through the lungs, or that something is interfering with the exchange of oxygen within the lungs. In either case, it is a very serious sign and must be treated immediately. A rough check of the circulation can also be made by pinching the mucous membrane on the inside of the lip until it blanches out, then watching to see how long it takes for the circulation to return. Another simple examination which can be performed without special equipment, yet is often overlooked by many veterinarians, is percussion. In this examination, the hand is placed over the chest and tapped with the fingers of the other hand. Normal lung tissue, being filled with air, has a hollow sound, while solid tissue, such as the
heart, tumors or other masses, have a dull sound. Using this procedure, it is often possible to outline the size of the heart, as well as the location of fluid levels, masses, and other abnormalities in the chest. Auscultation, the art of listening to the heart and lungs with a stethoscope, is a diagnostic procedure which requires no expensive equipment, but must be included with every physical examination.
A stethoscope is nothing more than a piece of rubber tubing attached to a chest-piece, or head, that is placed over the area of the chest that is being examined. The head is actually a resonant chamber designed to amplify sound, and is available in various shapes and sizes according to the likes of the individual doctor. Because the various sizes and shapes will intensify different sound frequencies, a stethoscope is invaluable for listening to the lungs and for checking the heart for abnormal sounds and "murmurs", as well as abnormalities in the rhythm. It is also useful for listening to the carotid arteries in the neck, where abnormal sounds and murmurs can sometimes be heard that can be helpful in the diagnosis of some heart and circulatory conditions. Except for a stethoscope, which every doctor must have to perform even the most basic physical examination, these are all diagnostic tests that can be performed without special equipment.

X-RAY

A chest x-ray is important in any evaluation of suspected heart or lung disease. It is especially useful in helping to confirm or diagnose suspected abnormalities
found during the routine screening procedures described above. X-rays are also valuable in outlining the size and shape of the heart and identifying which, if any,
of the chambers are enlarged. They can provide graphic illustrations of fluid levels in the chest, and aid in identifying masses and other abnormalities. They are also useful in helping to diagnose heart worm disease, especially the occult type, in which the circulating microfilaria which one looks for in a blood test, cannot be found.

ELECTROCARDIOGRAPHY AND PHONOCARDIOGRAPHY

An electrocardiograph is essentially a very sensitive instrument, capable of picking up scattered electrical currents produced by heart muscles, and turning them into a unified current that will produce a series of up and down lines on a piece of graph paper, each representing a specific phase of muscle contractions within the heart. The height and depth of these lines relative to a base line, the shape of the lines, and the amount of space between the lines all have very specific diagnostic meaning. It is essential when taking a tracing that the dog always be held as quietly as possible and in the same position, in order to have uniform conditions with which to compare one tracing to another. A vibrating base line, or a tracing that "roller-coasters" all over the tracing strip, increases the difficulty in making a diagnosis. An electrocardiographic unit is an excellent piece of equipment and one which would be desirable for every veterinary practitioner to own. They are quite expensive, however, and may be beyond the economic  capability of some veterinarians, especially those just starting a practice. In addition, one does not merely turn on the unit, take a tracing and come up with a diagnosis. Many of the EKG patterns are very subtle, requiring careful interpretation, so that extensive training is required before EKG's can be read accurately. Even with good training, it is not always possible for the general practitioner to make a diagnosis, and the tracing may have to be sent to a veterinary cardiology referral service for a final diagnosis. Fortunately, for those veterinarians unable to afford a unit or who may have trouble reading a particular tracing, an excellent source of back-up support is a company called Cardiopet. They have developed the technology to supply veterinarians with a small
electronic device that can pick up the electrical impulses from the heart and convert them to sound waves. These are sent over telephone lines to a receiver, which converts the information into a diagnostic EKG strip. Cardiologists within the company then interpret the findings, make a diagnosis, and recommend treatment procedures. An electrocardiogram is one of the best ways to evaluate abnormalities in both the rate and rhythm of the heart. The dog has what is referred to as a normal sinus arrhythmia and, unlike man, in which the same amount of time normally elapses from beat to beat, the amount of time between beats can vary considerably, although still within certain limits. Beyond these limits, the arrhythmia is abnormal, or pathologic, and the EKG is probably the best available means for determining the type of abnormality, as well as its cause and the location of the defect. The electrocardiogram can also give the veterinarian an excellent indication of the size and shape of the heart, its position within the chest cavity, and whether it tilts abnormally in one direction or another. Because there is so much variability in the size and shape of different breeds of dogs, as well as their chest cavities, the veterinarian must be familiar with all of the normal EKG variations, in order to determine what is abnormal.
The EKG will tell you what has happened in the heart in the past, as well as the condition of the heart at the moment the tracing is being made. And, although
treatment recommendations can be made based on changes that are already present, it will not necessarily prognosticate what will happen in the future. That is the reason why people with perfectly normal EKGs can walk out of doctor's office and suffer a serious heart attack the next day. A phonocardiograph, like an
electrograph, is an instrument that produces a visual graph of the heart sounds, and can help to identify the type and severity of heart murmurs. The instrument
is usually combined with the EKG unit, so that a simultaneous tracing of both the electrical impulses and the heart sounds will be recorded on the same graph
paper.

ECHOCARDIOGRAPHY

Echocardiographs are produced by ultrasonographic (ultrasound) diagnostic imagers. These instruments generate extremely high frequency sound waves that
are absorbed at different rates as they pass through the body. The information is fed into a computer, which then produces an image on a screen which can also
be photographed. Solid organs, such as the liver, will produce a different type of image than a hollow organ, such as the intestine, or a semi-solid organ with
hollow chambers, such as the heart. This is relatively new technology, and is not likely to be readily available at most veterinary clinics, both because the
equipment is very expensive and special training is required for the interpretation of the ultrasonagram. There are a number of large hospitals and teaching
institutions, however, as well as veterinarians specializing in radiology, cardiology and internal medicine, who have invested in the equipment, are skilled in
interpreting the findings, and are available for diagnostic consultation. The echocardiogram provides information not available with ordinary x-rays. While
x-ray gives an over-all picture of the heart, the image created is solid, and offers no diagnostic information about what is going on inside the heart, itself. The
ultrasonic picture, on the other hand, adds another dimension to the diagnosis. By allowing the doctor to "see" the heart valves and other internal structures, he can
more accurately evaluate the severity of a "leaky" valve, as well as other abnormalities within the heart.

ANGIOGRAPHY

Angiography is another diagnostic technique that is only available in a large institution or cardiac referral center, and consists of passing a long flexible tube,
called a catheter, through a vein or artery, and into the heart. Dyes are then injected into the catheter, and the path of the dye is followed with the use of
x-rays. A few institutions may even have equipment for producing cine-angiography. This is a motion picture x-ray which will show the movement of the dye as it passes through the heart and into the surrounding blood vessels, thus providing an even more accurate picture of the events going on in the heart. Obviously, angiography is not an everyday diagnostic procedure in small animal heart disease, but it is good to know that it is available if it is ever needed. In man, it is used most commonly for the diagnosis of coronary artery disease.
These are the arteries that supply blood to the heart muscle and, when blocked,can lead to heart attacks. Since coronary artery disease is not a common problem
in dogs, the principle use for angiography in this species is to identify defects in the heart that interfere with normal blood flow, such as holes in the wall separating the chambers of the heart, defects in heart valves, and obstruction with enlargement of the pulmonary artery. This is the major vessel carrying blood from the heart to the lungs and these changes are almost always due to heartworms.

SUMMARY

It is obvious that all of the above diagnostic equipment will not be found in the average veterinarian's office, nor is it even necessary or desirable to perform
every available diagnostic procedure for the average case. The most important thing to remember is that the general practitioner is not only trained and equipped
to diagnose most heart disease problems, he has the resources available to get additional help, if needed, for those occasional cases needing specialized diagnostic skill and care.

Continued in Part11