|What causes heart murmurs in dogs and cats and do they always point to something serious?|
A murmur can be caused by turbulent or fast blood flow within the heart. Such turbulence causes an abnormal sound that can be heard while listening to the heart with a stethoscope.
A heart murmur can be heard in normal hearts but most of the time murmurs are heard when the heart is structurally abnormal. Some of the causes of heart murmurs in normal hearts include anemia (low red blood cell count), fever, and elevated thyroid hormone concentrations (especially in cats). Other murmurs are caused by abnormal blood flow associated with a variety of cardiac diseases, including abnormal heart valves and different congenital defects.
Soft, "innocent" murmurs are usually heard in young puppies and kittens. These murmurs are not associated with cardiac disease and should disappear by approximately four months of age.
Congenital heart defects are commonly associated with loud murmurs in dogs and cats. A loud murmur in a kitten or puppy is never "innocent," and further evaluation is advised.
Specialized diagnostic tests, such as an echocardiogram (ultrasound of the heart), are used to diagnose congenital defects and determine prognosis and possible treatments.
The treatment of congenital heart disease depends on the type of defect. Some defects are managed medically while others are amenable to surgical intervention.
One of the most common congenital defects found in dogs that results in a very loud murmur is a patent ductus arteriosus (PDA). This is a blood vessel which normally closes at birth but if it remains open, then problems occur.
If it remains open, a large amount of blood is pumped through the lungs which normally would be pumped to the rest of the body. This results in extra work for the heart and without treatment, can lead to congestive heart failure (fluid in the lungs).
This congenital defect can be treated with surgery where the vessel is ligated (or tied off) or by placing an implantable device in the vessel which blocks the blood flow. This is done using a heart catheter (see pictures).
Below is an example of an angiogram that shows the abnormal blood vessel (PDA) outlined.
Below shows the placement of the occlusion device.
Below it shows that the blood vessel (PDA) is occluded.
The most common cause of a murmur in older dogs is degenerative valve disease (endocardiosis).
This disease is caused by an age-related thickening of the valves on the right and left sides of the heart. As a result of this thickening, the valves cannot close properly and begin to leak.
Below is a heart ultrasound (echocardiogram) image showing a leak of the mitral valve.
This leakage of blood causes an audible murmur. As the leakage worsens, the heart enlarges or dilates, and can eventually lead to congestive heart failure and fluid accumulation in the lungs. Although there is no cure for this condition, it can be managed for a period of time with various medications.
The most common heart disease associated with a murmur in adult cats is hypertrophic cardiomyopathy (HCM). This is a disease which affects the heart muscle as opposed to heart valves.
This disease results in thickening of the heart muscle and results in abnormal relaxation of the heart. Although many patients remain free of clinical signs for years, some cats develop clinical signs or symptoms. Some of these signs include breathing problems related to congestive heart failure. In addition, clot formation in the blood vessels of the rear limbs may lead to paralysis of one or both hind limbs.
Diagnosis of HCM requires echocardiography. Below is an ultrasound image of a cat with thickened walls of the heart secondary to HCM.
Routine examination by your pet's regular veterinarian is important for identification of cardiac murmurs. Once a heart murmur is heard in a pet, your veterinarian can explain the options for further testing. Such recommendations might include chest x-rays, an electrocardiogram (ECG), or a referral to a veterinary cardiology specialist for more advanced imaging.