What is Aortic Stenosis?
Aortic stenosis is an anatomic obstruction to flow from the left ventricle to the systemic circulation. This obstruction most commonly occurs as a congenital defect below the aortic valve (subvavlular), at the level of the valve (valvular) or above the valve (supravalvular). In rare cases aortic stenosis can occur secondary to neoplasia or endocarditis. The most common form of the disease is subvalvular aortic stenosis occurring as a thick fibrous tissue bands in the infundibular or subinfundibular region of the left ventricle directly below the valve, often with a normal aortic valve. The second common form of the disease is valvular aortic stenosis characterized by abnormally formed valve leaflets. Supravalvular aortic stenosis is rare. This disease is most commonly seen in large breed dogs with Golden Retrievers, Newfoundlands, Germans Shepherds, Mastiffs, Boxers and Great Danes being overrepresented breeds. No matter what the obstruction, the end result is an increase in left ventricular pressure in order to overcome the resistance caused by the obstruction. The left ventricle will hypertrophy (concentric) over time as a result of the elevated pressures. This pressure overload will rarely result in left-sided heart failure because diastolic filling of the left ventricle is not impaired unless the stenosis is very severe with secondary myocardial failure or mitral valve insufficiency. The stenosis is generally classified as mild, moderate or severe. Physical examination will reveal a systolic ejection murmur of the heart base with a crescendo or crescendo-decrescendo quality. The murmur can radiate towards the left apex and right thorax and can sometimes be heard radiating in the carotid arteries over the neck. Sometimes a basilar diastolic murmur of aortic insufficiency can also be heard.
Clinical signs are often only seen with moderate to severe stenosis and are most commonly exercise intolerance or sudden death related to myocardial ischemia or left heart failure secondary to pressure overload. Signs of left-sided heart failure include coughing, restlessness at night, difficulty breathing, inappetance, lethargy or exercise intolerance. Left-sided heart failure is rare and is most commonly seen if there is myocardial failure or problems with the mitral valve such as concurrent mitral valve insufficiency, dysplasia or degeneration.
Mild aortic stenosis often does not require treatment. Moderate to severe stenoses are often managed medically with beta-blockers in order to try to prevent arrhythmias that can lead to sudden death. These medications are used to decrease myocardial oxygen demand by decreasing heart rate and contractility, to decrease the risk of catecholamine effects on compromised myocardium and attempt to slow down the progression of myocardium ischemia. Balloon vavluloplasty is not recommended for aortic stenosis in order to open the narrowing because long-term success appears to be poor. Medical treatment for left-sided heart failure may also be indicated. The prognosis for mild aortic stenosis is good, while for moderate to severe the prognosis worsens with the severity as these animals are at a higher risk for sudden death.
Recheck examinations of your pet depend upon if your pet has been diagnosed with mild, moderate or severe aortic stenosis. Recheck of mild aortic stenosis can be performed one year after diagnosis when the pet is an adult to make sure there are no echocardiographic changes. If your pet has moderate or severe aortic stenosis, your pet should be rechecked on an annual basis.