Is there a blood test that will detect heart disease?
Yes. While veterinarians usually rely on stethoscopes, X-rays and ultrasounds of the heart to diagnose heart disease, there is now a blood test that can detect early changes in the heart before the dog shows any outward symptoms.
The proBNP is a simple blood test that was adapted from human medicine and can be used to predict the risk of developing congestive heart failure.
This test measures the presence of a particular type of hormone called NTproBNP, which is released into the bloodstream when the heart muscle is stretched or experiences stress. The NT stands for “natriuretic peptides.” These are substances made by the heart. Two main types of these substances are brain natriuretic peptide (BNP) and N-terminal pro b-type natriuretic peptide (NT-proBNP).
These cardiac hormones are involved in the maintenance of blood pressure, as well as water and electrolyte balance. They help the blood circulate more easily, and promote fluid and sodium excretion, which helps lower blood pressure.
Normally, only small amounts of BNP and NT-proBNP are found in the blood. Higher levels can mean the heart is under stress and not pumping as much blood as the body needs. This can be the result of stretching of the heart muscle due to muscle weakness seen in dilated cardiomyopathy, or thickening of the heart muscle that occurs with hypertrophic cardiomyopathy.
A condition known as mitral regurgitation occurs when the heart valves are not closing tightly. The sound of this swirling movement of the blood through the valves is what creates a heart murmur. Stretching of the heart muscle due to this abnormal blood flow will also increase NT-proBNP levels.
The highest concentrations of NT-proBNP are seen in dogs that develop congestive heart failure. The measurement of this hormone helps to distinguish congestive heart failure from primary respiratory disease. The NT-proBNP concentration in the blood correlates with the severity of the disease.
Several labs, including Antech and IDEXX, offer the proBNP test. It can be run by itself or as part of a chemistry/CBC profile. Interpretation of the results should take into consideration the clinical appearance of the patient. Dogs with severe arrhythmias, blood infections and pulmonary thrombosis may have high proBNP levels without congestive heart failure.
For high-risk breeds, such as Doberman Pinschers and Boxers, an increase in proBNP may be an early indication of occult dilated cardiomyopathy. Additional testing, such as electrocardiogram (ECG), echocardiography and Holter monitoring, would be recommended to identify any cardiac abnormalities.
What other tests are used to diagnose heart disease in dogs?
Auscultation is included in every thorough veterinary examination of your dog. This is the term for listening to the internal sounds of the body using a stethoscope. It is performed to examine the sounds of the heart and lungs in the chest, as well as bowel sounds in the abdomen. By placing the stethoscope over the heart on both sides of the ribcage just behind your dog’s elbow, your veterinarian will listen to the sound of the heartbeat, as well as the heart’s speed and rhythm. Cardiac murmurs, abnormally fast or slow heart rates, and irregular beats are detected, as well as abnormal lung sounds, including crackles and wheezes.
A dog’s normal heart rate will vary based on its size. Small dogs and puppies have heart rates of 120 to 160 beats per minute. Dogs weighing more than 30 pounds have heart rates of 60 to 120 beats per minute. The larger the dog, the slower the heart rate. A dog’s heart rate will normally speed up and slow down with each breath. The medical term for this is “sinus arrhythmia.” This is normal even though it is called an arrhythmia, and it does not require veterinary attention.
Radiographs, also known as X-rays, of the chest are taken to evaluate the size and shape of the heart. Certain cardiac diseases will show up as generalized enlargement of the heart or enlargement of specific heart chambers. The images will also point out any fluid in the lungs. The way the fluid is distributed throughout the lungs helps determine if it is due to cardiac disease, infection or cancer. X-rays are also used to monitor the progression of congestive heart failure.
Since radiographs give only a two-dimensional picture of the chest, a minimum of two X-rays are required for proper evaluation. One view is a “lateral” image taken with the dog lying on its side. The second view is taken with the dog positioned lying on its chest. This view is called a dorsal-ventral or D-V, top to bottom, spine to sternum view. In some cases, the opposite position, with the dog lying on its back, is taken. This is called a ventral-dorsal or V-D, bottom-to-top, sternum-to-spine view. Digital radiographs provide fine detail instantly to help diagnose cardiac disease.
An electrocardiogram (ECG) is the next test performed to assess the heart. When your dog’s heart beats, an electrical impulse is generated within a region of the heart known as the pacemaker. This impulse passes through the heart in a predictable manner that can be traced on an ECG recording.
By analyzing the electrical impulses produced as the heart beats, abnormalities within the heart can be found. These abnormalities include irregular heartbeats known as arrhythmias, abnormalities in the size and structure of the various heart chambers, and abnormal electrical conduction.
In most cases, an ECG can be performed in your veterinarian’s office. No special preparation is required for this procedure. The ECG electrodes are applied to your dog’s skin at the base of each of the four legs. Rubbing alcohol or a special conduction gel is applied to help the electrical impulse travel more easily.
Your dog’s electrical conduction may be traced for less than a minute or for several minutes, depending on what abnormality, if any, is seen on the display. In some cases, a smaller, portable ECG machine may be attached to your dog and left in place for 24 hours or more. This test, called a Holter monitor, will detect arrhythmias that are occurring less frequently and may be missed in a shorter-screening ECG.
Echocardiography is a type of ultrasound used to evaluate the heart, the aorta and the pulmonary artery. An “echo” complements other diagnostic procedures by displaying images of the working heart in motion. Heart chambers and wall dimensions can be measured. The physical structure and motion of the heart valves can be seen. Pressure differences, blood-flow volumes, and several measurements of heart function can be calculated. Heart disease, birth defects, diseases of the heart valves and cardiac tumors, as well as fluid accumulation around the heart, can be detected with an echo.
Echocardiography uses high-frequency sound to create an image of the heart. The machine’s small, handheld probe is placed on the dog’s chest. It delivers the sound waves through the body to the heart muscle and valves. The image created from the sound waves gives the veterinarian a detailed view of the moving heart and blood vessels.
Doppler echocardiography detects changing frequencies of the ultrasonic beam as it contacts moving red blood cells. This measures the speed of blood flow and can identify turbulent or high-speed flow created by leaking valves. This can be used to pinpoint the location of heart murmurs.
Occasionally, more specialized tests – such as cardiac catheterization, in which a thin, flexible tube is inserted and threaded through an artery in the heart, or nuclear studies, which are X-ray tests that include injection of radioactive isotopes – are necessary to diagnose cardiac disease.
The most routine of all cardiac diagnostic tests is a blood test for heartworm disease. This is a serious and potentially fatal disease in dogs in the United States and many other parts of the world. It is caused by foot-long worms that live in the heart, lungs and blood vessels. These worms severely damage the lungs and can result in heart failure. Mosquitoes transmit the heartworm larva to dogs and other mammals. In areas where mosquitoes are prevalent, dogs should be tested annually and given preventive medicine to avoid contracting this terrible disease.