(dilated cardiomyopathy, heart failure, and congestive heart failure)
This is a chronic condition in which a weakened heart does not pump enough blood to take care of the body needs. The body fluids tend to "back up" behind the heart much the same as a dam built across a river creates a lake. This puts pressure on the lungs and the liver and also further weakens the heart.
WHAT IS DILATED CARDIOMYOPATHY?
Cardiomyopathy is degeneration of the heart muscle. As a result of this degeneration, the muscle becomes thinner, particularly the thick muscle wall of the left ventricle. The pressure of the blood inside the heart causes these thin walls to stretch resulting in a much larger heart. This condition is described as Dilated Cardiomyopathy (DCM). This is the most common cause of heart failure in the large breeds of dogs. These include Boxers, Dobermans, and Great Danes. Occasionally medium sized breeds such as Cocker Spaniels, English Springer Spaniels and German Shepherd Dogs are also affected. Small breeds rarely develop DCM. Dilated cardiomyopathy may have a sudden onset of clinical signs. Some dogs may develop severe heart failure in only a few hours. Rapid, heavy breathing, a blue tongue, excessive drooling or collapse may be the first signs. Before a diagnosis of dilated cardiomyopathy is made, several tests are used that assess different aspects of heart function.
Auscultation which is listening with a stethoscope. This allows us to identify murmurs due to the improper closure of heart valves based on the murmur’s location and intensity. In addition, we can detect abnormal heart rhythms (arrhythmias and dysrhythmias) and evaluate lung sounds.
Blood and urine tests. We are especially concerned about liver and kidney function because these organs are often impaired in heart disease.
Chest X-rays. Chest radiographs allow us to examine the lungs and measure the size and shape of the heart. Dilated cardiomyopathy usually causes obvious enlargement of the heart, particularly the left side.
Electrocardiogram (ECG). This is an assessment based on the electrical activity of the heart. It allows us to accurately determine heart rate and to diagnose any abnormal rhythms.
Ultrasound examination (echocardiogram). This gives the most accurate determination of each heart chamber’s size and thickness of the heart walls. Measurements of the heart contractions can be taken to evaluate the heart’s pumping efficiency.
WHAT IS HEART FAILURE?
Heart failure is the inability of the heart to maintain sufficient blood circulation to meet the body’s needs. Heart failure usually describes a failure of the heart muscle (myocardial failure) or heart valve (mitral valve insufficiency). This can affect the right or the left ventricle. Sudden cardiac arrest can occur for a variety of reasons. Cardiomyopathy is the leading cause of acute heart failure (heart attack) in dogs. In humans a “heart attack” usually refers to myocardial infarction (MI). This is death of the cells in an area of the heart muscle (myocardium). This is usually due to oxygen deprivation caused by obstruction of the coronary blood vessels. MI is not a common disease of dogs, but it can occur. In dogs heart failure is more commonly due to either DCM or to congestive heart failure (CHF) or mitral valve disease.
What is the mitral valve?
The heart has four chambers. The upper chambers are called atria and the lower chambers called ventricles. The heart is also divided into right and left sides. Blood flows back from the tissues and organs of the body via the vena cava into the right atrium. It is stored briefly in the right atrium and then pumped into the right ventricle, which pumps the blood into the lungs where it is oxygenated. It flows from the lungs back into the left atrium and then passes into the left ventricle which is surrounded by the largest and strongest of the heart muscles. This muscle mass is necessary to generate sufficient pressure to pump the oxygenated blood to the body. The atrium and ventricle are separated by a valve, which prevents the blood from flowing back into the atrium when the heart contracts. The valve between the left atrium and ventricle is the mitral valve. Because this valve must withstand tremendous pressure throughput life, it may fail and begin to “leak” as the pet ages. This can be detected with a stethoscope and is called a mitral murmur. Mitral valve disease is the most common cause of heart failure in small dogs. In large dogs dilated cardiomyopathy is the most common cause of heart failure.
Approximately 10% of all small breed dogs will develop mitral valve insufficiency (MVI). This is often described as a “heart murmur”. MVI is initially asymptomatic, or having no obvious signs. As time goes on, the leak becomes more severe and as more blood leaks back into the atrium this results in reduced pumping efficiency. Eventually congestive heart failure occurs. This can be months or years from the time when the murmur was first detected. The most common clinical sign of congestive heart failure is coughing or difficulty breathing. This is due to the accumulation of fluid in the lungs called pulmonary edema. Additionally, many dogs with CHF will tire more easily, have reduced stamina and not engage in playing or walking as they once did. If any of these signs develop in a pet with a heart murmur, notify your veterinarian immediately.
WHAT IS CONGESTIVE HEART FAILURE?
Congestive Heart Failure (CHF) is a term that refers to the heart’s inability to pump adequate blood to the body. There are many causes of CHF in dogs. The two most common causes are mitral valve insufficiency (MVI) and dilated cardiomyopathy (DCM). Clinical signs vary depending on whether the dog has left- or right-sided heart failure. The most common symptoms are decreased stamina, coughing or difficulty breathing.
Right-sided congestive heart failure causes poor venous return to the heart. In other words, when the heart contracts instead of the right ventricle pushing the blood through the lungs for oxygenation, some returns to the right auricle. This blood is unable to be cleared from the systemic circulation and consequently becomes “congested”. Fluid accumulates in the abdomen and/or the chest cavity, interfering with the function of the organs in these areas. The abdomen may become enlarged with fluid called ascites. Fluid may also leak from veins and swelling may appear in the limbs (peripheral edema). When CHF involves the left ventricle, blood is not pumped into the systemic circulation and builds up in the lungs. Fluid then seeps into the lung tissue resulting in pulmonary edema. This causes coughing and difficulty breathing.
CHF is most commonly caused by valvular insufficiency. It is estimated that 80% of the canine CHF cases are caused by MVI. However, there are many other causes. Disease of the heart muscle (cardiomyopathy), irregularities of rhythm and narrowing of some of the major blood vessels can also cause CHF. CHF usually results in coughing, ascites, exercise intolerance, general lethargy, weakness and weight loss despite having an enlarged abdomen due to ascites. The normal pink color of the mucous membranes may become pale or bluish color. As with any heart problem, diagnosis involves several tests: auscultation or listening to the heart with a stethoscope is the first step in diagnosing heart disease. Pulse quality and heart rhythm are also assessed during auscultation. Other diagnostics may include chest x-rays (which are then used to determine the size and shape of the heart and the presence of fluid in the lungs), blood and urine tests (to give an indication of any other disorders in the body, liver and kidney function are often impaired in patients with heart disease), an electrocardiogram or ECG (this measures the electrical activity of the heart and allows accurate determination of both heart rate and rhythm, any abnormal rhythms can be detected and evaluated), and ultrasound examination (echocardiogram) which utilizes sound waves to evaluate the heart’s contractions and to measure the amount of blood pumped by the heart.