Basic heart function
The heart is divided into four chambers. The right atriumreceives unoxygenated blood which then goes past the tricuspid valve into the right ventricle. From here, blood is pumped into the lungs through the pulmonic arteries as it passes by the pulmonic valve. Blood flows to the lungs where it is oxygenated. The blood returns via pulmonary veins into the left atrium. From here, blood flows past the mitral valve into the left ventricle. From here, blood is pumped out to the rest of the body via the aorta as it passes by the aortic valve. This sequence of events is coordinated by an electric impulse triggered by the SA node to result in a regular rhythmic lup-dup of the heart as it consistently relaxes and contracts.
Heart disease results from any abnormality of the heart. While heart disease can result in heart failure, it can be present and never lead to heart failure. Murmurs can be associated with heart disease that may be minor or serious in nature. Arrythmias are usually associated with serious heart disease. The heart disease may or may not necessitate treatment.
Heart failure is the end-result of heart disease and occurs when the heart is decompensating from its heart disease and is working inefficiently to cope with the body's needs. It is associated with signs of congestion/edema, poor perfusion and low blood pressure. This condition always necessitates treatment.
Signs
Some pets may have significant heart disease without signs. However, their condition can change quickly with stress or exertion as the heart starts to fail.
Most dogs with significant heart failure will show some or all of the following signs- coughing, especially at night, fatigue, tiring with exercise, a change in gum color from pink to a bluish color, difficulty breathing or rapid, shallow breathing at rest. These signs occur due to accumulation of fluid in or around the lungs and in the abdomen.
Most cats, however, show no signs before complete failure occurs. They can go from being apparently normal cats to open mouth breathing or fast, shallow breathing or having inabilityto use their legs when they have a clot (emboli) originating from the heart that lodges in their aorta. Cats can also suddenly die at home and pass away before anything can be done to help them.
Problems with the heart
Arrythmias
These may be primary, that is, associated with the heart directly and resulting from a heart condition. Arrythmias can also be secondary to problems with other organs in the body or occur in reaction to toxins or anesthesia.
Arrythmias may be heard during a routine physical exam where the animals shows no outward signs of a problem; they may be heard when an animal presents for fatigue, collapse or "seizure" like signs.
Arrythmias are categorized according to the chamber with which they are associated. Arrythmias of the atrium are called supraventricular, while arrythmias of the ventricles are called ventricular. Bradyarrythmia is a decreased heart rate, while tachyarrythmia is an elevated heart rate.
Murmurs
Murmurs result when there are changes within the heart. These can be from thickening of the valves (endocardiosis), narrowing near the valves (stenosis), thickening or thinning of the chambers (cardiomyopathy) or infection of the heart (endocarditis).
Murmurs may be heard during a routine physical exam where the animal has no symptoms of a problem (asymptomatic). Murmurs may be heard when the animal is showing signs of heart failure (fatigue, difficulty breathing, fainting or coughing).
Sometimes, with soft murmurs in puppies and kittens, they can be "innocent", that is, they will eventually disappear and cause no problems for the animal. A murmur that develops later in life, after six months of age, is more likely to be from disease. Murmurs are graded in loudness on a scale from 1 to 6, one being a soft, barely heard murmur to six being able to be heard without a stethoscope. While murmur loudness is useful in its description, it often doesn't correlate directly with the severity of the heart problem.
Murmurs can indicate a primary heart problem or can be secondary to other conditions such as anemia in dogs and cats (when the blood is thin and more prone to turbulence) or hyperthyroidism in cats (when having elevated levels of thyroid hormone put an excessive strain on the heart).
Congenital Heart Conditions
Animals can be born with a heart condition resulting from a congenital malformation. These are seen in young animals and can be hereditary. For this reason, these animals should not be bred. Certain breeds of dogs and cats are more likely to have certain congenital heart conditions, but even mixed breeds can be affected. Some common congenital heart defects are:
Patent Ductus Arteriosis (PDA)
A shunt is present in the fetal state that fails to close in the young animal, resulting in a direct connection between the pulmonary artery and aorta. The flow of blood is usually left-to-right; occasionally, though, if pressure builds up in the lungs, the flow can be right-to-left. These conditions are treated differently.
Pulmonic Stenosis and Aortic Stenosis There are areas of constriction or narrowing near or at the pulmonic or aortic valves.
Atrial Septal Defect (ASD) and Ventricular Septal Defect (VSD)
There are openings due to an incomplete wall between the two atria or two ventricles.
Mitral or Tricuspid Valve Dysplasia
There are malformed mitral or tricuspid valves that result in abnormal blood flow.
In general, subaortic and pulmonic stenosis and patent ductus arteriosus are the most common congenital abnormalities in dogs, and ventricular septal defect and tricuspid valve dyplasia are the most common congenital abnormalities in cats.
Hernias
Peritoneopericardial diaphragmatic hernias refer to the condition in which an animal is born with an opening of the diaphragm and the pericardial sac, allowing herniation of abdominal contents into the chest cavity and into the sac that surrounds the heart.
Acquired Heart Conditions
Most heart disease in animals is acquired, that is, associated with a condition that develops over time. Certain breeds of dogs and cats are more likely to have certain acquired heart disease.
The most common conditions are:
Mitral valve disease (MVD)
This occurs when there is thickening of the mitral valve on the left side of the heart; this results in abnormal blood flow. It is also known as mitral regurgitation.
Cardiomyopathy
These are disease of the heart muscle. This condition is common in older small breed dogs.
- Dilative, the most common form in dogs, is when the chamber walls are thin and the chamber size is enlarged. There is a higher incidence in Boxers, Doberman pinschers, Cocker spaniels and Great Danes.
- Hypertrophic, the most common form in cats, is when the chamber walls are thickened, and there is less room for blood inside the chamber.
- Restrictive and mixed forms of cardiomyopathy are two other forms that can occur in cats.
Pericardial disease
This refers to accumulation of fluid in the sac that surrounds the heart (pericardial sac); this can occur from cancer, trauma, infection or for no known reason (idiopathic).
Heartworm disease
This can occur in dogs and is acquired via mosquitoes; cats living in areas frequented with mosquitoes carrying the heartworm larvae can occasionally acquire this disease. Heartworms, left untreated, will lead to heart failure.
Cardiac tests
Tests are required to differentiate between the different forms of heart disease and indicate what type of treatment is needed.
Radiographs
These show the overall heart size and arteries and veins of the lungs. It can show if one side of the heart is larger than the other and suggest what chambers may be enlarged. It can also check for the presence of fluid associated with the lungs (pulmonary edema or effusion) and for the presence of abdominal fluid (ascites) and other organ enlargement, especially, the liver.
Echocardiogram
This is an ultrasound of the heart, the most useful test there is to determine the presence and type of heart disease. Itallows for the measurement of the chambers (the wall thickness) and for the evaluation of heart valves' efficiency. It indicates overall heart performance and helps to dictate what type of treatment is needed. Follow-up echocardiograms show if the treatment is working or not.
Electrocardiogram (ECG or EKG)
This shows the heart's rate and rhythm and helps to determine what type of arrythmias are present. It can also suggest if there is chamber enlargement.
Blood and urine tests
A blood panel and urine test showing organ function is valuable in evaluating the body as a whole. Sometimes, the heart can affect other organs; sometimes, the animal has concurrent disease. It is important to have a "baseline" of the body'sfunction, before heart medication is started. Some values, especially kidney function and electrolytes, may need to be rechecked over time once treatment is started.
Blood pressure
Hypertension can occur with both heart and kidney disease and can make the animal's condition worse. High blood pressure is treatable and it's control may help the pet's heart condition.
Monitoring
Home monitoring
Since a pet is more relaxed at home, heart and respiratory rates taken at home are more accurate than those in the hospital. It is important to learn to monitor a pet's breathing pattern since this can be a clue of fluid accumulation in the chest and even a pet's heart rate can indicate if the heart disease is under control or not.
A heart rate can be measured by placing a hand on the pet's chest and inside the thigh to feel the femoral artery. An inexpensive stethoscope can serve this purpose also. Count the
heart rate for 15 seconds and multiply the number by four to get the number of beats per minute. Similarly, the respiration rate can be counted. A normal resting heart and respiratory rate for a dog, respectively, is 100-120 beats per minute and 12-20 respirations per minute. A normal resting heart and respiratory rate for a cat, respectively, is 120-160 beats per minute and 24-32 respirations per minute.
Hospital monitoring
Rechecks for radiographs to evaluate lung changes, ultrasound to evaluate heart function, rechecks of blood pressure levels, and blood and urine tests to evaluate organ function while on medications are all important to assuring the pet a good quality of life while coping with heart disease or heart failure. The goal is to make the heart last longer and prevent complications of heart disease and failure by giving daily medications.
Treatment
Treatment is usually medical and is directed at helping the heart cope with the results of its inefficient state. There are many human drugs that are used to manage pets with heart disease and in heart failure. However, is surgery is rarely of help; only in patients with left to right patent ductus arteriosis (PDA) may benefit from surgery.
Diet
Since sodium/ salt can retain water and further increase work on the heart, feeding a prescription low sodium diet is recommended for pets in heart failure. However, it does not appear to be beneficial in preventing heart failure. Diet changes for a pet with heart problems include not feeding salty snacks and commercial dog and cat foods since they tend to have a lot of sodium. However, low sodium diets are less palatable, and some pets refuse to eat them. Examples of low-sodium prescription diets are: Hill's H/D for dogs and Purina's CV for cats. For dogs, there is also a home-made diet formulation.
Diuretics
This is a class of drugs that result in increased urine output as they "draw" fluid out of the lungs. Examples of commonly used drugs are lasix (Furosemide or Disal), spironolactone
(Aldactone) and hydrochlorothiazide (Chlorothiazide). These drugs are overall safe, but animals must be monitored for dehydration, electrolyte imbalances and for the worsening of kidney failure, if present.
Angiotension converting enzyme (ACE) inhibitors
This is a class of drugs that reduce the work load on the heart and lower blood pressure. Examples of commonly used drugs are enalapril (also known as Vasotec or Enacard) or benazapril (Lotensin). These drugs are overall safe, but animals must be monitored for negative effects on the kidneys and excessive lowering of blood pressure.
Digitalis
This is a class of drugs that increase the strength of contractions of the heart. They also have anti-arrythmic effects and are used to control supraventricular arrhythmias. Examples of commonly used drugs are digoxin (Lanoxin) and digitoxin (Crystodigin). These drugs can be toxic and must be used carefully. Blood levels can be monitored as a guide to dosing the drug. Excessively high levels can cause a decreased appetite, kidney dysfunction or ventricular arrhythmias.
Calcium channel blockers
This is a class of drugs that relax the heart tissue and decrease the rate of an excessively fast heart rate, such as in cases of hypertrophy, so the heart can fill more efficiently. They can also be used to treat hypertension. Examples include dilitazem (Cardizem) and amlodipine (Norvasc). These drugs are overall safe but blood pressure must be monitored.
Beta adrenergic blockers
This is a class of drugs that decrease the heart rate and relax the heart muscle in cases of hypertrophy. Examples include atenolol (Tenormin) and sotalol (Betapace).
Oxygen therapy
While it is helpful in an emergency situation for a pet in fulminant heart failure in a hospital, it is not practical for home application.
Nutritional supplements
Taurine- in the past, taurine deficiency was a common cause of dilated cardiomyopathy in cats. Due to supplementation in cat foods, it is a rare condition now. Some forms of dilated cardiomyopathy in dogs, especially that occurring in Cocker spaniels, can be responsive to taurine supplementation.
Carnitine- Some dogs, especially Boxers with dilated cardiomyopathy, may benefit with supplementation of carnitine.
If you have questions regarding this disease, please don't hesitate to call your veterinarian.
The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.
Tags:Congenital Heart Defects,Arrythmias,Heart Diseases
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