Subvalvular aortic stenosis is probably the second most common congenital heart defect in dogs. Larger breed dogs are more susceptible, and it has been proven to be inherited in some breeds. To understand this disease, it is important to understand the aorta’s role in the normal heart.
The outflow to the left ventricle must be adequately sized, given the fairly large volume of blood that flows through it at a high pressure. Dogs most commonly suffer from the presence of an obstruction just below the aortic valve (figure), called subvalvular aortic stenosis or subaortic stenosis (SAS). This obstruction is caused by a ring or ridge of stiff tissue. The heart must work harder to pump such a large volume of blood through a narrowed opening. The severity of this disease depends on how narrow the stenotic portion is and, thereby, how much additional pressure must be generated by the left ventricle to allow an adequate blood flow through the sudden narrowing. Any additional pressure represents extra work for the heart, which can lead to enlargement of the left ventricle.
Although subaortic stenosis is a congenital defect (i.e., it is “present” at birth), its severity can progress over time (let’s say from several months to a few years). Therefore, puppies with this disease may sound and act completely normal when they are very young (approximately 1-3 months of age) and can develop a heart murmur later on. If unnoticed, this condition can trigger changes to the heart muscle that can have lethal consequences. Early diagnosis of this condition is very important because it allows early initiation of medical therapy and discourages the dog’s use for breeding purposes. It is essential that any dog with subaortic stenosis be evaluated by a cardiologist as soon as possible.
In mild cases, subaortic stenosis usually does not require treatment. In most patients with moderate to severe disease, drugs known as beta blockers are frequently prescribed. These drugs maximize oxygen delivery to the left ventricle so that it can better cope with its increased workload. Other medications may be necessary if a patient has an irregular heart rhythm or develops heart failure.
Balloon valvuloplasty can be considered as a palliative (i.e. temporary and partial) treatment in severe cases. In this procedure a cardiologist inserts a catheter with an inflatable balloon across the narrow left ventricular outflow tract. The balloon is then inflated to stretch the stiff tissue causing the narrowing. Treatment of subaortic stenosis with valvuloplasty is unfortunately not as rewarding as with pulmonic stenosis, thereby is not performed routinely, but reserved for selected patients.
Prognosis is guarded for all patients with severe subaortic stenosis. Sudden death is possible even with treatment; however, your cardiology team can maximize your pet’s quality of life and help your pet live as long as possible. Heart failure is rarely seen with this disease.
Severe narrowing of the aorta outlet