Glossary of Terms
Ascites is fluid accumulation within the abdominal cavity. This occurs in right sided congestive heart failure. As the pressures build up in the right side of the heart, which occurs in heart failure, fluid starts to leak out of the veins and into the abdomen. This fluid accumulation, in large amounts, can push the diaphragm and compresses the chest making it difficult to expand your lungs when you breathe. The fluid is able to be seen with radiographs or ultrasound.
The heart normally beats at a regular constant rhythm called sinus rhythm. When this rhythm is disrupted it is called an arrhythmia. Arrhythmias can occur for many reasons. Two tests will likely be recommended if an arrhythmia is heard. First, an electrocardiogram must be performed because the type of arrhythmia can not be diagnosed by just listening. The electrocardiogram allows the Doctor to evaluate the electrical conduction system in the heart and determine what arrhythmia is present. Second, an echocardiogram may be performed to determine if the arrhythmia is due to a diseased heart.
CONGENITAL HEART DISEASE
Congenital anomalies are diseases that the patient is born with. Patent ductus arteriosus (PDA) is the most common congenital heart defect in dogs while ventricular septal defect is the most common congenital heart disease in cats.
- SUBAORTIC STENOSIS
Subaortic stenosis (SAS) is a congenital anomaly that involves the tissue just below the aortic valve. This tissue is abnormal and it causes a narrowing, or stenosis, where the blood leaves the heart. The left ventricle then has to push harder to force blood through this small hole. With time the left ventricle can become thickened from this increased work. Arrhythmias, sudden death, and congestive heart failure are common with severe aortic stenosis. Unfortunately, there is not a good surgical procedure to cure this disease. Instead, we rely on medical therapy to reduce the amount of obstruction and minimize arrhythmias. Dogs that are in the mild to moderate range may live normal lives. Dogs in the severe range are at a high risk of sudden death before the age of three. They are also at risk of going into congestive heart failure.
- PATENT DUCTUS ARTERIOSUS
In utero, blood is allowed to bypass the lungs through the ductus arteriosus. This ductus should close shortly after birth. If the ductus remains open it is called a patent ductus arteriosus (PDA). Blood then shunts from the aorta to the pulmonary artery and back into the left side of the heart. This results in volume overload to the left side and can lead to congestive heart failure. PDA is diagnosed using echocardiography. Radiographs should also be taken to evaluate the lung fields, overall heart size, and vessel size. There are two methods to correct a PDA. The ductus can either be surgically ligated or it can be occluded with the use of embolization coils. Prognosis without correction is guarded; 50-64% will die within the first year. The remainder will likely go into congestive heart failure. Prognosis with correction is excellent and most dogs go on to live a normal life.
- PULMONIC STENOSIS
Pulmonic stenosis (PS) is a congenital defect involving the pulmonic valve. The valves normally open and close to allow blood to flow in one direction. In pulmonic stenosis the valves are usually fused. Blood then has to squeeze through a much smaller area than normal. This causes pressure overload in the right side of the heart and the heart must get bigger and work harder to continue to pump blood through this narrowing (stenosis). With time arrhythmias can occur as well as congestive heart failure. Pulmonic stenosis is diagnosed using echocardiography. Doppler echocardiography allows measurement of blood flow through the stenosis. This can be converted into a pressure gradient and allows for classification of the stenosis. Normal pressure gradients between the pulmonary artery and the right ventricle are less than 20 mmHg. Mild PS is 20-50 mmHg. Dogs with mild PS may live normal lives. Moderate PS is when the pressure gradient is between 51-80 mmHg. Dogs with moderate PS may live normal lives but are at risk for developing congestive heart failure and arrhythmias later in life. Severe PS is having a pressure gradient over 80 mmHg. Sudden death, arrhythmias, and congestive heart failure are usual outcomes for dogs with severe pulmonic stenosis. There are several surgical treatments for severe pulmonic stenosis. The treatment of choice is balloon valvuloplasty. If balloon valvuloplasty is not an option other surgical procedures can be recommended.
CONGESTIVE HEART FAILURE
The heart's purpose is to pump blood, containing oxygen and nutrients to the body. When the heart can not meet these demands, the heart is said to be "failing." Heart failure can occur for many reasons including cardiomyopathies or valvular disease. When fluid begins to accumulate within the lungs or body cavities it is then called congestive heart failure.
Dilated Cardiomyopathy (DCM) is a heart disease characterized by having a large heart that does not contract well. With time the pressures within the heart build up and this leads to congestive heart failure. In some dogs arrhythmias can also occur causing collapse, weakness, and sudden death. DCM is diagnosed using echocardiography. Radiographs are used to diagnose congestive heart failure and overall heart size. If an arrhythmia is suspected, an electrocardiogram may also be performed. There is no cure for idiopathic DCM. Therapy is aimed at making the patient feel better and live longer than if no therapy was instituted. Prognosis varies from breed to breed and can range from months to years.
Doppler echocardiography allows the Doctor to track the blood flow through the heart and great vessels. Doppler imaging measures the velocity of blood flow and based on the color, it is able to determine if the flow is normal (laminar) or turbulent. Pressures within the heart and great vessels can also be determined using the velocity obtained. Doppler measurements are commonly performed during the echocardiogram.
An echocardiogram is an ultrasound of the heart. It allows the Doctor to evaluate not only the heart size but also the heart function. It also allows visualization of the heart valves, heart muscle, and chambers. A number of views are obtained from both the right and left sides of the chest. This test is non-invasive and usually does not require shaving or sedation. An echocardiogram is performed if there is a murmur or arrhythmia detected on physical examination. While it is an excellent diagnostic tool it is not the only test that may need to be performed.
ELECTROCARDIOGRAM (ECG or EKG)
An electrocardiogram is used to assess the heart's electrical activity. This test is also non-invasive and does not require shaving or sedation. Probes are attached to the skin and waveforms are produced. The Doctor is able to look at these waves and determine how the electrical conduction system of the heart is working. An electrocardiogram can be performed for many reasons but the most common reason is if an arrhythmia is suspected.
Hypertrophic Cardiomyopathy (HCM) is the most common acquired heart disease in cats. It is characterized by having a thickened heart muscle that does not relax well. As the pressures within the heart increase the top chamber of the heart dilates and congestive heart failure ensues. Echocardiography is used to diagnose HCM. Radiographs allow visualization of the lungs and overall heart size. Prognosis varies and depends on the patient's response to therapy. Many cats will stabilize and live for several years with the disease, while others may progress more quickly. Cats with HCM are at risk of developing arrhythmias, sudden death, congestive heart failure, and blood clots.
KIDNEY FUNCTION & CONGESTIVE HEART FAILURE
In heart failure the heart does not supply the body, including the kidneys, with the appropriate amount of oxygen and nutrients. The body tries to compensate for this decrease in perfusion but these compensatory mechanisms can cause further damage to the kidney. In congestive heart failure medications are given that are potentially detrimental to the kidney in some animals. Therefore, it is very important to monitor the kidney function when an animal is in congestive heart failure and on these medications.
MITRAL VALVE DISEASE
In mitral valve disease, the valve that separates the left atrium from the left ventricle is affected. The valve is present to prevent backflow of blood when the heart contracts. As the valve degenerates fluid leaks back up into the atrium, or top chamber of the heart. This causes an overload of volume and with time the pressures increase and the chambers enlarge. If fluid leaks into the lungs (pulmonary edema) congestive heart failure is present. An echocardiogram identifies the abnormal valve and backward flow. It also allows assessment of the heart function. Radiographs (X-ray) allow assessment of the lungs and it is used to determine if congestive heart failure is present. Prognosis varies from dog to dog. Some animals remain stable for years where as others will progress rapidly. We can not cure mitral valve disease and unfortunately it is a progressive disease. Mitral valve disease is medically managed and the goal of therapy is to help the patient feel better and live longer than if no therapy was instituted.
A murmur is a sound that may be heard when listening to the heart. Murmurs are graded on a scale of 1 to 6. 1/6 being very quiet and 6/6 being so loud that the murmur can be heard with the stethoscope off of the chest. The loudness or intensity of the murmur does not indicate the severity of the disease. A murmur is not a disease; instead it indicates the presence of turbulent blood flow within the heart. When a murmur is heard an echocardiogram may be recommended to determine the cause of the murmur.
Pleural effusion is fluid accumulation outside of the lungs, within the thoracic cavity. This occurs in right sided congestive heart failure. As the pressures build up in the right side of the heart, which occurs in heart failure, fluid starts to leak out of the veins and into the chest. This makes it hard to breathe as the fluid compresses the lungs. The fluid is able to be seen with radiographs or echocardiogram.
Pulmonary edema is fluid accumulation within the lungs. This occurs in left sided congestive heart failure. As the pressures build up in the left side of the heart fluid starts to leak out of the lung blood vessels and into the lung tissue. This makes it very hard to get enough oxygen when you breathe and can also cause coughing. The fluid is able to be seen on a radiograph (X-ray).
Radiographs, or X-rays, are taken to evaluate the heart's shape and size as well as to assess the lungs. Taking a radiograph is the only test that can diagnose pulmonary edema, or congestive heart failure. It does not assess heart function.