What is behind the heart murmur?

Heartpic

So has this happened to you? You take your pet to the veterinarian and he or she is spending a lot of time with the stethoscope over the heart. Then the next statement you are told is “your pet has a heart murmur “. So what does that mean? Does that guarantee your pet has heart disease? Is your pet going to be very sick or even die from the murmur? I am sure these and many other questions run through your mind when you hear the term “heart murmur”. The goal of this article is to help you with these questions and many more regarding heart murmurs.

What is a heart murmur?

A murmur is an extra or unusual sound heard when the heart beats. It is caused by a disturbed blood flow through abnormal valves, blood vessels, or a defect in a structure inside of the heart.

Some common causes of murmurs in pets

Mitral and Tricuspid valve dysplasia

The mitral and the tricuspid valves control the direction of blood flow through the chambers of the heart. They act as “dams” preventing blood from flowing backwards when the heart is pumping. In heart disease, these valves can begin to break or wear down causing leakage or back flow of blood. This is also known as regurgitation. It is more common for the valve on the left side of the heart (mitral valve) to wear down. Since blood comes from the lungs on the left side, when there is regurgitation, it causes increased pressure on the lungs. This increased pressure can cause the blood vessels in lungs to leak fluid leading to a condition called pulmonary edema.

Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy is most common in cats, but it can occur in dogs as well.  Abnormal thickening of the muscle on the left side of heart occurs with this heart condition. Thickening of the muscle can be caused by abnormalities with the heart muscle, or abnormalities with hormones like an overactive thyroid. This thickening of muscle does not allow as much blood to enter the left side of the heart leading to increased pressure for the lungs. It also causes damage to the mitral valve leading to valve leakage.

Dilated cardiac myopathy

This heart condition is most common in large dogs. In this condition all the chambers of the heart are abnormally enlarged or dilated. The dilation of the chambers of the heart leads to poor contraction of the heart muscles which leads to poor blood flow to the rest of the body. There is a genetic component and seems to be a breed predilection for Dobermans, Boxers, and giant breed dogs with this condition

Juvenile heart murmur

This is described when a murmur is heard in a young pet. When puppies are first born they are usually born with a hole or defect in the upper chambers of the heart called the atrium. This is called an atrial septal defect. This defect typically closes within the first week after birth. In some dogs, this closure is delayed and results in a murmur. This only requires further investigation if the murmur persist beyond 4 months of age.

How do you diagnose the cause of a murmur?

Chest x-rays- These allow for visualization of the heart size and if there are any abnormalities with the lungs or blood vessels.

Cardiac ultrasound- This is the best way to see inside the heart outside of open heart surgery. This involves the use of sound waves to produce an image of inside the heart. Any abnormalities of the valves, dysfunction with contraction of the heart, or increase in the size of the chambers of the heart can be detected. Also, the location of a murmur can be detected using a special feature called a color Doppler which highlights abnormal blood flow.

EKG- Allows for measurement of the electrical activity of the heart. During a normal heart beat the upper part of the heart sends a signal to the lower part telling it when to contract. The EKG can detect any abnormalities in this system which are called arrhythymias.

Treatment for Heart Disease

So now your veterinarian has discovered what is causing the murmur so what is next? Depending on the cause of the murmur and its severity your veterinarian may place your pets on medication.

Two primary goals of cardiac medication is to improve cardiac output and to decrease the amount of stress or pressure that the heart needs to pump against.

Improve cardiac muscle contractions

One way to improve cardiac output is to improve how efficient that the heart muscle contracts. There are 2 common drugs that are often prescribed to achieve this. Pimobendan and digoxin. These work by blocking an important enzyme which allows an increase in calcium in the muscle allowing for improved contraction.

Improved cardiac output by dilating blood vessels.

Another way to improve cardiac output in pets is to dilate the major blood vessels responsible for taking blood to and from the heart. A common class of drugs to achieve this effect is called ace Inhibitors. These drugs block hormones responsible for causing these blood vessels to constrict. The common drugs that are prescribed in this class are benazepril, enalapril, and lisopril.

Diuretic therapy

Diuretic therapy may be used in pets who have advanced cardiac disease. They draw fluid out of the blood vessels therefore decreasing the volume of blood coming to the heart. They also may help decrease fluid in cases where heart disease cause fluid build up in the lungs or abdomen. Common diuretics prescribed include lasix, furesomide and spironolactone.

Final perspective

If your pet has a heart murmur, this does not always mean certain death for your pet. You may want to find out what the cause of the murmur by having the diagnostic tests performed mentioned in the article. Remember without doing tests, your veterinarian cannot truly determine how serious the murmur is. Also these tests can help provide the best treatment for your pet’s heart disease.

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