What causes Heart failure?
Heart failure generally falls into 3 categories:
- Muscle failure
- Valvular Failure
- Congenital abnormalities
Muscle failure is generally divided into dilated or hypertrophic cardiomyopathy. Dilated cardiomyopathy is a disease seen mostly in dogs and is common in certain breeds (particularly large and giant breeds).
Cats were commonly afflicted with this problem years ago until a dietary deficiency of taurine was found to be causative in most cases. A defect in the heart muscle causes the walls to become stretched out and thin. In this state, it cannot function adequately as a pump. Usually this becomes a problem when it affects the left ventricle and leads to left sided heart failure.
In hypertrophic cardiomyopathy, the heart muscle becomes too thick to be an efficient pump. The muscle can become so big that there is littleroom left in the ventricular chamber for the blood. As a result, blood backs up into the left atrium and back into the lungs. This disease is more prominent in cats than dogs. Sometimes it is caused by excess thyroid hormone (hyperthyroidism), which can be treated with drugs, surgery or radioactive iodine. Pets with this disease are prone to having thromboembolism (strokes).
The valves in the heart can cause problems in two ways, by becoming leaky (either due to deterioration with age, or due to lesions on the edges of the valve caused by bacterial infections) or by being constricted.
Leaky valves are common in older pets and in certain breeds. Because some of the blood pumps back up through the leaky valve, the heart has to work harder to meet the body’s demands. The ventricular muscles will thicken to help compensate for the increased work, but eventually, they may fail and the pet will go into heart failure. If the mitral valve is leaky (left side of the heart), the left atrium may become enlarged as the blood squirts up into it through the valve. The left atrium lives right below the trachea. When it enlarges, it may cause a chronic cough as it hits the trachea.
Constricted valves are usually the cause of a congenital defect. The valves affected are usually the outflow valves (Aortic valve on the left, or Pulmonic valve on the right). The ventricles have to work much harder to pump blood through a narrow valve. Initially, they will thicken to compensate for the added load, but eventually they will fail and the pet will experience heart failure.
Congenital abnormalities range from malformed valves to holes in the inner walls of the ventricles or atria. Congenital defects are usually diagnosed within the first few months of life as the pet will be weaker than littermates and have exercise intolerance. Some congenital abnormalities can be corrected surgically while others are often fatal.
What are the symptoms of heart failure?
Many of the symptoms of heart failure are common to all the different causes we have discussed. They include:
- Increased thirst & urination
- Difficulty sleeping through the night
- Weight loss
- Shallow breathing
- Exercise intolerance
As heart failure progresses the symptoms usually worsen. Sometimes, the pet will have extreme difficulty breathing and the tongue may turn bluish purple.
How do our veterinarians diagnose heart failure?
The diagnosis of heart failure starts with a complete history from the owners and a thorough physical examination. Frequently, our veterinarians will hear a loud murmur in the heart indicating a leaky valve or other defect. In severe conditions, we may hear sounds of moisture in the lungs. Dogs in right heart failure may have fluid buildup in the abdomen (ascites), which is visible during the exam. Next, our veterinary team turn to radiographs (x-rays) to evaluate the chest and belly as well as blood and urine tests. Radiographs show us the size and shape of the heart and the condition of the lungs. Blood tests tell us what is going on in the other major organ systems. If the heart is suspect, we perform electrocardiograms and echocardiography. The ECG tells us about the rhythm of the heart and the relative size of the chambers. Echocardiography is the most effective modality for determining cardiac function. The ultrasound study allows us to visualize the heart as it beats. Our veterinarians can visualize abnormalities (valve defects, tumors etc), measure the size of the walls and chambers and determine if the heart is pumping efficiently.
How do our veterinarians treat heart failure?
Treatment for heart failure varies with the cause of the failure. Most often, our veterinary team will use drugs to reduce the water content in the body (diuretics like furosemide) along with drugs that reduce the blood pressure against which the heart has to pump (ACE inhibitors like Enalapril). Sometimes we will use drugs to slow the heart rate to allow it to pump more efficiently (calcium channel blockers and beta-blockers). For other conditions, our veterinarians may need to use drugs to help maintain the proper rhythm of the heart. Along with drug therapy, we usually use special diets that are restricted in salt to help reduce the body’s fluid load. Strict rest is always part of the treatment protocol if the pet is in actual failure.
What is the prognosis for heart failure?
Again, the prognosis for heart failure varies with the cause of the failure. Early detection and intervention will help to prolong the life of the pet with heart disease. This is one reason why our veterinarians recommend physical exams yearly for pets under 9 years of age and twice yearly for our older patients. Many pets with heart failure can be helped with the therapies mentioned above. The survival times for these patients are quite variable and have to be taken on a case-by-case basis. Survival times may vary from a few days to a few years. In time, most of these hearts will fail completely in time, however, the pet may have good quality of life until that occurs if they respond positively to the therapy.