Pulmonic Stenosis in Dogs
What dogs get this disease?
This congenital disorder is most often identified in brachyocephalic (e.g. bulldogs, Boston terriers), terriers (Jack Russel terriers), Samoyeds, and Labrador retrievers. Other breeds can also be affected such as boxers and Newfoundlands.
Pulmonic stenosis is a congenital heart defect of the semilunar valve that is between the right ventricle and the pulmonary artery (great vessel that takes blood to the lungs). The leaflets of this valve are thickened and/or partially fused together. Sometimes the supporting structure known as the annulus is also narrow. Dogs that have this congenital defect have a wide range of stenosis to include very mild to severe obstruction to blood flow from the heart to the lungs. This defect may be associated with other congenital defects too (e.g. ventricular septal defect, overriding aorta, subaortic stenosis). Because this disease is associated with certain breeds it is likely that it is at least in part due to a mutation in as yet unidentified gene.
Many dogs have no clinical signs. Dogs with mild disease never develop any problems and may live a normal lifespan. However, dogs with advanced disease may have exercise intolerance, collapsing, arrhythmias, or heart failure.
Virtually all dogs with clinically important pulmonic stenosis will have a cardiac murmur heard when the chest is listened to with a stethoscope. This is auscultation of the chest. Often, but not always, how loud the murmur is in this particular disease correlates with severity. An important example of the exception to this general statement is with tetralogy of Fallot where several congenital defects are present together with pulmonic stenosis.
- Radiography and angiocardiography. Radiographs which are made with x-rays provide information regarding the size and shape of the silhouette of the heart. Angiocardiography is a type of radiography whereby contrast (dye) is injected into the vasculature to see the stenosis. This is most often done at the time of treatment using balloon valvuloplasty.
- Echocardiography An important diagnostic tool to fully characterize the structure and function of the pulmonic valve and the support structures involves the ultrasound of the heart known as echocardiography. This test permits the examination not only of the muscle and valve, but also of the blood flow (Doppler echocardiography). Determination of the blood flow across the stenotic valve is important to learn the severity of the pulmonic stenosis because this guides the recommendations for treatment. The cardiologist will be able to determine the gradient across the stenotic valve. This is usually the first parameter used to decide if the dog requires treatment with balloon valvuloplasty. In most cases dogs with a gradient above 80 mmHg are recommended to have treatment when the stenosis is primarily valvular. Dogs with a gradient of less than 50 mmHg do not usually require treatment. When the gradient is in the middle, other factors are taken into consideration for the next step towards or away from the catheter procedure.
- Electrocardiography An electrocardiogram (ECG) may be preformed to further characterize dogs with pulmonic stenosis; however, this test is usually not as important as the physical examination, radiograph, and echocardiogram. Other tests may be ordered to determine the status of other body systems and to insure that all are functioning adequately.
Balloon valvuloplasty is the treatment used for valvular pulmonic stenosis. Not every dog with this defect can be helped by this procedure. Some dogs have dramatic improvement while others have adequate results. Echocardiographic examination can give indicators of dogs that are most likely to be helped. This treatment involves the passage under general anesthesia of special catheters which when an attached balloon is inflated, tears the restricted valve leaflets. Measurements of the pressure gradient before and after treatment give information as to the success of the treatment. This treatment involves specialized training of the veterinary cardiologists and the use of expensive specifically ordered catheters for each patient. Our service has published several manuscripts concerning the treatment of pulmonic stenosis. Some dogs may be treated with beta-adrenergic blockers (e.g. atenolol) either with or without the balloon valvuloplasty.
The prognosis depends on the severity of the disease and the response to treatment.
How should an affected dog be monitored?
The frequency and intensity of the monitoring depends on each patient, the severity of the disease, the response to treatment, and the status of other body systems. Usually after the balloon valvuloplasty a dog is examined 3 months later and then yearly.