Murmurs, which are extra vibrations of the heart that are produced as a result of a particular disturbance in the blood flow. These audible noises are classified according to a variety of characteristics, including their timing. For example, systolic murmurs occur when the heart muscle contracts while diastolic murmurs occur when the heart muscles relax between beats. A third type of heart murmur is known as continuous because the murmurs occur throughout most, if not all, of the cardiac cycle.
Symptoms and Types of Heart Murmurs
The symptoms that are associated with heart murmurs depend greatly on a variety of different characteristics, including their grade, location, and configuration. Also, a dog that has heart murmurs which are associated with a structural heart disease may also show signs of congestive heart failure such as being exercise intolerant, having weakness, and coughing.
The grading scale of heart murmurs is divided into six categories, or grades, of heart murmur. These are:
- Grade I --- heart murmurs which are barely audible even with a stethoscope.
- Grade II --- Soft heart murmurs which can be heard with a stethoscope.
- Grade III --- Murmurs which have intermediate loudness. This is the most common type of heart murmur.
- Grade IV --- Loud murmurs that radiate widely. These can often be heard on the opposite side of the chest.
- Grade V --- Very loud murmurs can usually be heard through the stethoscope just before it makes contact with the animal's chest. Also, the vibration of the heart murmur can be felt through the animal's chest wall.
- Grade VI --- These heart murmurs are extremely loud and can often be heard without the use of a stethoscope. Also has a very strong vibration which can easily be felt by placing a hand on the animal's chest.
Aside from grading heart murmurs they are also classified according to their configuration. Three configurations exist and are listed below:
- Plateau murmurs have uniform loudness and are typical of blood regurgitation through an abnormal valvular orifice (regurgitant murmurs).
- Crescendo-decrescendo murmurs get louder and then softer and are typical of ejection murmurs due to turbulent forward flow.
- Decrescendo murmurs start loud and then get softer and are typical of diastolic murmurs.
Causes of Heart Murmurs
Basically there are three main causes of heart murmurs in dogs. These are:
- A disturbance of the blood flow associated with a high flow volume through a normal or abnormal heart valve or with some type of structure vibrating in the blood flow.
- Flow disturbances that are associated with regurgitation of the blood flow due to an incompetent heart valve, patent ductus arteriosus, of a defect in the heart septum which is the wall that separates the left and right sides of the heart.
- Flow disturbances that are associated with an outflow obstruction or excessive forward flow through diseased and damaged heart valves. Also occurs when blood flows into a dilated great blood vessel.
Most heart murmurs, however, are a direct result of specific conditions and diseases. The following are normally associated with the causes of systolic heart murmurs:
- Dynamic subaortic stenosis
- Systolic anterior mitral motion (SAM)
- Heartworm disease
- Aortic stenosis
- Atrial septal defect
- Ventricular septal defect
- Pulmonic stenosis
- Tetralogy of Fallot
- Mitral and tricuspid valve endocarditis (inflammation of the inner part of the heart)
- Mitral and tricuspid valve heart failure
- Cardiomyopathy and aortic valve insufficiency
- Mitral and tricuspid valve dysplasia
- Dynamic right ventricular outflow obstruction
Continuous Heart Murmurs (also known as To-and-Fro Heart Murmurs) may be the result of the following conditions:
- Ventricular septal defect with aortic regurgitation
- Aortic stenosis with aortic regurgitation
- Patent ductus arteriosus
Diastolic Heart Murmurs are usually caused by the following conditions:
- Mitral and tricuspid valve stenosis
- Aortic and pulmonic valve endocarditis (inflammation of the inner layer of the heart)
Diagnosis of Heart Murmurs
In order for your veterinarian to properly diagnose exactly what is causing the heart murmurs in your dog he or she must differentiate between a wide variety of abnormal heart sounds. In addition, she or he must also be able to differentiate between the various abnormal lung and heart sounds of which many sound alike. In order to accomplish this the veterinarian will listen to see if the timing of the abnormal sounds is correlated with respiration or heartbeat timing.
Another way to determine the underlying cause of the heart murmur is for the veterinarian to listen to not only the timing during the cardiac cycle but to the location and radiation of the heart murmur sounds. To accomplish this a variety of tests may be performed including chest X-rays, Doppler studies, as well as echocardiography. In addition the veterinarian may also order a complete blood count which will either support or refute the heart murmur as being caused by anemia.
Treating Heart Murmurs
If heart failure is not evident your dog will be treated as an outpatient for its heart murmur condition. The actual course of treatment that will be prescribed will depend greatly on the type of heart murmur and the clinical signs shown by the animal. Puppies and young adult dogs with low grade heart murmurs (grades I & II) may require very little or no treatment at all. Low grade murmurs in dogs usually clear up by their selves within six months.
More mature dogs or dogs with a higher grade of heart murmur will be placed on medications that will help to either control the murmur's severity or to counteract the actual underlying cause of the heart murmur.
Dogs that have been diagnosed with heart murmurs will require routine diagnostic imaging for the remainder of their lives. This is usually done approximately every six months.
Dogs that have heart murmurs can and do lead a normal life. Usually the symptoms can be controlled with the proper medication. This is usually the case with dogs that suffer from low grade heart murmurs.
Dogs that have a higher grade heart murmur should lead a life that is somewhat quieter so as to not aggravate the condition. These dogs will probably require medication for their complete lives to keep the murmur down to a minimum.
Dogs that have heart murmurs because of congestive heart failure will require a very quiet life style. These dogs should not do any activity that require great effort. They should be kept as comfortable as possible and may also require smaller meals throughout the day.