A 4 month old male Newfoundland presents to you for vaccination. A left basilar systolic heart murmur is noted that radiates well to the right chest. Thoracic radiographs reveal a normal cardiac silhouette and no evidence of pulmonary vascular or interstitial disease. The EKG is normal.
Echocardiography is of outstanding value to confirm a presumptive diagnosis of aortic stenosis or subaortic stenosis. In this disorder, short of cardiac catheterization, there is no other method available to confirm the existence of aortic stenosis.
Although routine Two-dimensional Echocardiography may give us clues to the existence of aortic stenosis, in many cases this test is inconclusive. In severe cases of aortic stenosis, the Two-dimensional exam may reveal left ventricular concentric hypertrophy and a discrete subvalvular lesion, in the case of subaortic stenosis. The M-mode Echocardiographic examination may reveal a clue to the presence of co-existent aortic valve insufficiency (diastolic fluttering of the anterior leaflet of the mitral valve) premature closure of one cusp of the aortic valve. As well this modality should indicate evidence of left ventricular concentric hypertrophy.
The Doppler Echocardiographic study yields data which usually definitively establishes the diagnosis of aortic stenosis and provides evidence of the severity of the disorder. Doppler Echocardiography determines the velocity of blood flow as it exits the left ventricle. The normal maximal velocity of blood flow exiting the left ventricle is approximately 1.5 meters per second. Thus velocities detected in excess of 1.5 m/s suggest stenosis of the column of blood flow (especially velocities in excess of 2.0 m/s). In addition, we have noted that aortic valve insufficiency occurs in a large percentage of cases of subaortic stenosis. It appears that this aortic valve insufficiency does not significantly hemodynamically embarrass the performance of left ventricle, however it does frequently serve as a useful marker to the presence of concurrent subaortic stenosis. As the subaortic stenosis progresses the maximal velocity of blood flow across the stenotic region increases. Severe stenosis is characterized by a velocity of blood flow of 5 m/s or greater.
In this dog the Doppler study revealed a velocity of blood flow exiting the left ventricle of 3.5 m/s and the presence of aortic valve insufficiency.