Murmurs, Arrythmias, Heart Disease, & Failure

The heart is divided into four chambers. The right atrium receives 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 inability to 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. It allows 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’s function, 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 its control may help the pet’s heart condition.