MENDING A BROKEN HEART STARTS WITH FINDING THE BREAK

In Star Trek, The Next Generation, Dr. Crusher waves a hand-held probe over the body of her patient while a technician, sitting at a nearby computer, reads off more vital findings than could be obtained in three days of laboratory testing today. An impossible dream? A figment of a Hollywood screenwriter’s imagination? Ridiculous science fiction verging on fantasy? Maybe and maybe not.

With the advent of echocardiology, more commonly known as cardiac ultrasound, physicians and veterinarians alike now have a non-invasive method which allows them to literally “peer into the heart” of their patients.

In recent years, Doppler echocardiology has made it possible not only to see the structures of the heart but also to obtain important information regarding the flow of blood through it. With the use of two different methods of Doppler echocardiology, color flow and spectral, the physician can obtain a color-coded image of blood as it flows through the heart including areas of abnormal turbulence, then determine the blood

flow velocity in specific areas of the heart to access the extent of the abnormality.

CARDIAC ULTRASOUND COMES TO THE CANINE

Up until the mid 70’s, veterinarians were limited to using their physical diagnostic skills coupled with radiology and possibly electrocardiography to help them diagnosis diseases or abnormalities of their patients’ hearts. Then in the late 70’s, veterinarians began working with ultrasonic equipment passed down from the human medical field and by the mid 80’s, with the development of 2-dimensional ultrasonic equipment, veterinarians were able to get detailed pictures of the heart, inside and out.

According to Dr. Mark Kittleson, Professor of Medicine at the University of California at Davis and a diplomate of the American College of Veterinary Internal Medicine, “With 2-dimensional ultrasound, you can see the anatomy of the heart, the chambers, the valves moving, the relationship of them to each other. You can see lesions, holes between chambers of the heart, abnormal valves, chambers that have enlarged.”

Such detail is not available by other diagnostic means. Conventional radiology is limited to outlining the heart, lungs, and other structures of the chest cavity. Although changes in the shape and size of the heart can be discerned by x-ray, it is impossible to see the inner workings of the heart. Contrast on an x-ray is a result of the different densities of the objects being x-rayed. Since heart muscle and blood have almost the same density, the heart shows up on an x-ray as a solid mass.

Electrocardiograms (EKG’s) measure the electrical output of the heart muscle and again, although it can point to abnormalities of the heart’s size, shape, and function, EKG’s can not give the detailed information of a cardiac ultrasound.

Echocardiology uses ultrasonic sound waves which are reflected off the structures being examined and can distinguish objects that are less than 1-mm apart. The reflected waves are then converted into a picture which can be viewed on a monitor, photographed or videotaped for future study.

With conventional echocardiology, there are two techniques commonly used, M-mode and 2-dimensional. The newest innovation, Doppler echocardiology also has two different techniques, spectral and color flow. All four techniques give important information but in a different way. Depending on the case, one or more of these methods may be utilized in diagnosing abnormalities of the heart as well as giving information needed to make a prognosis.

“M-mode echocardiology, instead of showing you the whole anatomy, takes just one tiny little slice.” Says Dr. Kittleson. “2-dimensional echocardiology gives you the anatomy of the heart at the usual frame rate of a VCR.”

These two techniques are often used together. With 2-dimensional echocardiology, the clinician gets a clear picture of the heart and can then accurately measure the sizes of the chambers of the heart as well as the thicknesses of the walls with M-mode echocardiology. Chamber size is important in diagnosing many heart conditions since the heart often enlarges one or more of its four chambers to compensate for an abnormality.

Doppler echocardiology is used to measure blood flow in the heart. Color flow echocardiology gives the clinician a color display of the blood as it circulates through the heart. With this technique, blood flowing away from the measuring device is colored blue and blood moving towards the device is colored red. Also, the faster the blood is moving the brighter the hues. Turbulent blood flow which is an indication of heart disease is often characterized by high-velocity blood flow with many different velocities and will show up as a mixture of various reds and blues.

As with conventional echocardiology, Doppler echocardiology’s two techniques give different information. Spectral Doppler echocardiology gives very specific blood velocity measurements of isolated areas while color flow Doppler echocardiology gives an overall picture of the blood flow.

AN ECHOCARDIOGRAPHIC EXAMINATION

Echocardiographic equipment isn’t found in every small animal veterinary practice. A new state-of-the-art echocardiograph may cost over $200,000, making it economically prohibitive except for research and teaching institutions or very large veterinary practices.

Therefore, your veterinarian may refer the case to a larger facility such as a veterinary college. In some areas of the country, cardiac specialists travel to the private practices in the area carrying their portable ultrasound equipment with them. Increasingly, private veterinary practices are purchasing their own equipment, often used equipment obtained from human medicine. Since the field of echocardiology is advancing quickly with new and improved equipment regularly coming on the market, good used equipment is often available. Even used, the $15,000 -$30,000 price tag for an ultrasound machine is no small investment for the small animal practitioner.

Most commonly an echocardiographic exam is reserved for a patient with a heart murmur which is picked up during a physical exam; either a young dog with a congenital disease or an older pet suffering from congestive heart failure. With both sets of patients, after the thorough history and physical exam is completed, chest x-rays and an electrocardiogram may be performed to determine if an echocardiogram is indicated.

In most cases, the echocardiogram is performed with the dog fully awake. Prior to the ultrasound, the dog’s side may be shaved although in many cases, the only preparation needed is the application of an ultrasound gel to the chest. The animal is placed on his right side on a Plexiglass table which has areas cut out of the Plexiglass. The dog’s chest is placed over one of the cut-out areas so that the echocardiograph transducer can be applied between the ribs on the surface lying on the table. The transducer must be applied to the chest in an area where the heart is in contact with the chest wall. If the ultrasonic wave comes in contact with the air of the lungs, it is quickly dissipated resulting in no picture. Taking the echocardiogram reading from the side lying on the table allows for a larger “cardiac window” — the area in which the heart is in direct contact with the chest wall.

With the 2-dimensional echocardiogram, the ultrasonic beam “slices” through the heart resulting in 2-dimensional pictures. Since there are an infinite number of slices that could be viewed, the operator moves the transducer to capture standard planes which can be compared with echocardiograms taken of normal dogs.

Depending on what is found with the 2-dimensional study, M-mode echocardiology may be employed to determine the sizes of the heart chambers. If the equipment has Doppler capability and blood flow data is needed, color flow Doppler is performed next. If hemodynamic irregularities are detected, more specific measurements may be made using the spectral Doppler technique.

After the right side is completed, the dog is turned over and the procedure is repeated on the left side. Depending on the condition which is being studied and the degree to which the animal cooperates, this procedure may take anywhere from twenty minutes to an hour.

Fees for an ultrasound exam can vary tremendously depending on how extensive the testing is, how long the procedure lasts and who is performing it. Teaching institutions like veterinary colleges, where the fees are often lower, may charge from $80 to $120. A typical range for private veterinary practices would be $125 to $200. Not bad when you compare it to human medicine where a twenty-minute ultrasound exam performed by a technician may run $700 or more.

ECHOCARDIOGRAM USES

As mentioned before, the two groups of canine patients where echocadiography is indicated are:

1) Young animals with heart murmurs as a result of congenital deformities and

2) Older animals with leaky heart valves resulting in heart murmurs and congestive heart failure.

Some of the congenital heart defects which may be diagnosed by echocardiography are patent ductus arteriosus, aortic stenosis and sub-aortic stenosis, pulmonic stenosis, ventricular septal defects, atrial septal defect and tetralogy of Fallot.

Of these, one of the most common congenital conditions in which echocardiology is used for diagnosis as well as screening of litters is sub-aortic stenosis. This condition is most commonly seen in Newfoundlands, Rottweilers, Golden Retrievers, and Boxers. In screening for this condition, the veterinarian will examine a litter, auscultating the chest for any signs of a heart murmur. In puppies, murmurs are occasionally detected which have no underlying pathology. For this reason, an ultrasound exam is a useful screening procedure since it can differentiate between those which are serious and those which aren’t.

Doppler echocardiology may be useful, particularly in milder forms of subaortic stenosis in which anatomical changes may be minimal. By measuring the blood flow velocity, it is possible to determine if the velocity is within normal limits. Since stenosis of a blood vessel will result in increased blood velocity, measuring the blood flow velocity can be diagnostic of even mild cases.

The most commonly seen acquired heart abnormality in dogs is mitral valve regurgitation. This condition is particularly common in small breed dogs such as miniature Poodles, Dachshunds, Lhasa apsos, and Chihuahuas usually after about seven years of age. The mitral valve of the heart degenerates, losing its ability to act as a one-way valve. The resulting heart murmur may be detected on a routine annual physical exam or in more advanced cases the pet may be presented with signs of congestive heart failure, such as a chronic cough and difficulty breathing.

Since the mitral valve is easily visualized with echocardiology, this procedure is useful in diagnosing the condition as well as determining the severity of the damage.

Pericardial effusion, in which the membranous sac around the heart fills with fluid, is another condition in which echocardiology can play an important diagnostic role. This condition may result from either pericarditis, an infection or inflammation of the sac, or as the result of a tumor. Distinguishing between these two is important since pericarditis is a relatively benign condition compared to a tumor. Prior to echocardiology, the veterinarian would have to withdraw the fluid with a needle and syringe, then fill the pericardial sac with carbon dioxide followed by x-rays in an attempt to detect a tumor.

“The method wasn’t all that great as far as being able to pick-up all the tumors whereas ultrasound is great.” Says Dr. Kittleson. “It’s very unusual for us to miss a tumor these days.”

Dr. Kittleson also points out that there are two types of tumors which are commonly seen in this area, heart base tumors, which are slow growing benign tumors and hemangiosarcomas which are much more malignant. Since these tumors grow in different areas of the heart, echocardiology is also able to tell clinicians which type of tumor they are dealing with as well as determine the prognosis for the patient.

ECHOCARDIOLOGY OF THE FUTURE

Although it may be a few years before the scenes of Star Trek’s Dr. Crusher are reality, innovations in echocardiology will certainly continue with 3-dimensional echocardiograms a very real possibility.

One day, you may be able to walk into your veterinarian’s exam room and instead of him showing you a set of x-rays, there may be a holographic image of your dog’s heart suspended in space. It will be a full-size scale model which, with a push of a button, can be opened and examined by you and your veterinarian while the real heart which it represents beats steadily away in your dog as he rests in a holding cage in the next room, waiting for the help he has come to expect from his owner and doctor.

THE END