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Left ventricular emptying may be obstructed at 3 locations: 1) subvalvular, also called subaortic, consisting of a fibrous ridge of tissue within the left ventricular outflow tract; 2) valvular; and 3) supravalvular or obstruction distal to the aortic valve. The most common form in dogs is subaortic stenosis. Breed predilections have been identified for Boxers, Golden Retrievers, Rottweilers, German Shepherds, and Newfoundlands. |
| Pathophysiology: |
| Aortic stenosis induces left ventricular hypertrophy, the degree of which depends on the severity of the stenosis. In severe cases, left ventricular output may be decreased, especially during exercise. The major ramification of left ventricular hypertrophy is the creation of areas of myocardium with poor perfusion. Myocardial ischemia is a major factor in the development of serious life-threatening ventricular arrhythmias. |
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| Clinical Findings and Treatment: |
| Clinical signs do not consistently parallel the severity of stenosis. There may be a history of syncope and exercise intolerance. Animals with no history of illness may die suddenly and the defect is first detected at necropsy. An ejection-type systolic murmur heard best at the aortic valve area is present. The intensity of the murmur correlates fairly well with the degree of stenosis and may increase as animals mature, reflecting progressive stenosis. Puppies without
detectable murmurs should not be considered free of disease until they reach 6 mo of age because the murmur may be very soft in the first months of life. In moderate to severe cases, femoral pulse strength is diminished. Electrocardiography may show left ventricular enlargement (tall R waves in lead II) and ventricular premature complexes that may increase in frequency with exercise. Holter monitoring should be used in syncopal animals or in patients with severe disease to define
the presence of any arrhythmias, assess arrhythmia severity, and assist in determining the risk of sudden death. A recheck Holter monitor may be considered following initiation of antiarrhythmic therapy to assess efficacy. Radiographically, there is variable left ventricular enlargement and poststenotic dilatation of the aorta. Doppler echocardiography is recommended to confirm the diagnosis and rule out other cardiac abnormalities. The degree of left ventricular hypertrophy and
peak systolic flow velocity through the defect can help determine stenosis severity. |
| Treatment options include medical management of arrhythmias to reduce the incidence of clinical signs of exercise intolerance or syncope, balloon valvuloplasty (typically not very effective), and surgical resection (high morbidity and mortality, high cost, and lack of significant gradient reduction). The use of β-blockers such as atenolol has been advocated to control ventricular arrhythmias in patients with subaortic stenosis and to presumably reduce the chance of sudden
death. Mildly affected animals commonly require no treatment and the prognosis can be fair to good in very mildly affected patients. Affected animals should not be used for breeding. |
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