A veterinarian often diagnoses cardiovascular disease by reviewing the medical history and signs, conducting a physical examination, and interpreting the results of specific tests or imaging procedures. The physical examination includes using a stethoscope to listen to the sounds made by the dog's internal organs, especially the heart, lungs, and abdominal organs, and examining parts of the body by feeling with hands and fingers to distinguish between solid and fluid-filled swellings. Imaging techniques include x-rays; electrocardiography (recording electrical activity of the heart); and echocardiography (a type of ultrasonography). Most cardiovascular diseases can be diagnosed by physical examination and x‑rays. Electrocardiography is specific for diagnosis of arrhythmias. Echocardiography is excellent for confirming tentative diagnoses, for detecting heart tumors, or for detecting pericardial disease. Occasionally, more specialized tests such as cardiac catheterization (using a thin flexible tube inserted and threaded through an artery into the heart) or nuclear studies (x‑ray tests that include injection of radioactive isotopes) are necessary. Heartworm disease is diagnosed best by performing a blood test to detect the presence of female heartworms.
Electrocardiograms can show cardiac arrhythmias and other abnormalities in dogs.
Common Types of Imaging Used to Diagnose Heart Disease
X-rays
X-rays (also called radiographs) of the chest frequently help diagnose heart disease in pets. Finding generalized enlargement of the heart or enlargement of specific heart chambers makes the presence of heart disease more likely. The images may also provide clues as to the specific disease present. For example, fluid in the lungs is a common finding in congestive heart failure. Although chest x-rays are useful in evaluating patients with heart disease, they have certain limitations. The presence of fluid in the lungs does not definitively confirm a disease originating from the heart or exclude another origin such as pulmonary (lung) disease. Also, assessment of overall heart size and the size of specific heart chambers is typically far less accurate than testing by echocardiography (ultrasonography).
Electrocardiography
Electrocardiography is the recording of the heart's electrical activity from the body surface with the use of electrodes. It can be used to identify heart arrhythmias such as bradycardia (slower than expected rhythm), tachycardia (faster than expected rhythm), or other abnormalities of rhythm (such as sinus arrhythmia or sinus arrest).
Electrocardiography can also detect conduction disturbances, or failures of the electrical signals that cause the heart to contract to pass through the heart tissue. These include first-, second-, and third-degree atrioventricular block.
Finally, electrocardiography can identify chamber enlargement, which is indicated by waveform abnormalities shown on the electrocardiogram recording. Different readings suggest enlargement of the different chambers. While the electrocardiogram may suggest chamber enlargement, chest x-rays and echocardiography (ultrasonography) are more sensitive.
Echocardiography
Echocardiography is a type of ultrasonography used to evaluate the heart, the aorta, and the pulmonary artery. Echocardiography complements other diagnostic procedures by examining and displaying the working heart and moving images of its action. Heart chamber and wall dimensions can be determined; the physical structure and motion of valves can be seen; and pressure differences, blood flow volumes, and several measurements of heart function can be calculated. There are 3 main types of echocardiography: 2-dimensional, m-mode, and doppler. Two-dimensional echocardiography provides a wedge-shaped, 2-dimensional image of the heart in real-time motion. M-mode echocardiography is produced by a 1-dimensional beam of ultrasound that penetrates the heart, providing an “ice-pick view.” The tissue interfaces that are encountered by the beam are then plotted on a screen. This mode of evaluation is typically used to measure chamber dimensions, wall thickness, valve motion, and the dimensions of the aorta and pulmonary artery. Doppler echocardiography employs the principle of changing frequency of the ultrasonic beam after it contacts a moving red blood cell to measure the speed of blood flow and thus identify turbulent or high-speed flow. This can locate heart murmurs.
Cardiac Catheterization
Cardiac catheterization involves the placement of specialized catheters (thin, flexible tubes) into the heart, aorta, or pulmonary artery. Cardiac catheterization may be performed when other diagnostic tests are insufficient to identify specific heart abnormalities or are unable to identify the severity of a lesion. It may also be used for presurgical evaluation, treatment, and in clinical research. Diagnostic and presurgical cardiac catheterization, however, have largely been replaced by echocardiography (see above).
Many heart disorders are more common in certain breeds. For example, mitral regurgitation is more common in Cavalier King Charles Spaniels and in older, male Cocker Spaniels. Older Miniature Schnauzers may develop specific types of arrhythmias, and tetralogy of Fallot is more common in young Wirehaired Fox Terriers. Knowledge of these and other breed associations with heart disease can often help your veterinarian make a diagnosis.
General Signs of Cardiovascular Disease
Dogs showing signs of heart disease may have a history of exercise intolerance, weakness, coughing, difficulty breathing, increased breathing rate, abdominal swelling (caused by fluid pooling in the abdomen), loss of consciousness due to lack of blood flow to the brain (fainting), a bluish tinge to skin and membranes due to a lack of oxygen in the blood, or loss of appetite and weight. More rarely, swelling of the legs, jaundice (yellowing of the eyes, skin, or membranes), or coughing up blood or bloody mucous may be noted.
Last full review/revision July 2011 by Davin Borde, DVM, DACVIM; Clay A. Calvert, DVM, DACVIM; Benjamin J. Darien, DVM, MS, DACVIM; Jorge Guerrero, DVM, PhD, DEVPC (Ret); Michelle Wall, DVM, DACVIM
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