Subaortic stenosis is an autosomal-dominant (incomplete penetrance) congenital heart disease of dogs characterized by a narrowing of the descending aorta below the left ventricular outflow tract of the heart.
It is one of the most common congenital heart diseases in large-breed dogs and is commonly reported in the Boxer, German Shepherd, Golden Retriever and Newfoundland dog where death is common at a young age.
The lesion is a subvalvular fibrous membrane that runs across the ventricular septum and onto the septal mitral valve leaflet, causing septal hypertrophy and outflow tract tunneling fibrosis and obstruction. This onvariably leads to aortic insufficiency, mitral valve regurgitation
In some dogs, concurrent cardiac anomalies such as atrial septal defect, mitral valve dysplasia, ventricular septal defect, tricuspid dysplasia, Situs inversus totalis and left coronary aneurysmal dilation can also be present.
Dogs with subaortic stenosis are typically asymptomatic or only mildly exercise intolerant, even with severe stenosis.
Clinical signs are normally seen in young dogs (1 - 2 years of age) but can present at an older age with symptoms of generalized weakness, exercise intolerance, syncope, weakened femoral pulses and pale mucus membranes. A cough may be present intermittently.
A tentative diagnosis can be established by auscultation of a holosystolic ejection murmur with radiographic evidence of cardiomegaly.
Definitive diagnosis requires use of M-mode and Doppler echocardiography, which usually demonstrates varying degrees of ventricular free wall and septum thickening, mitral regurgitation and premature systolic closure of the aortic valve, indicating thickening and dynamic obstruction.
A differential diagnosis would include ventricular septal defect, double-chambered right ventricle, hyperthyroidism, cardiomyopathy, Duchenne muscular dystrophy, endocarditis, pulmonic stenosis, mitral valve endocardiosis and infections with Dirofilaria spp.
The prognosis for dogs with subaortic stenosis declines as the severity of the stenosis worsens. Dogs with severe stenosis (left ventricular — aortic pressure gradient > 80 mmHg) have a high risk of sudden death by 3 years of age. Dogs with less severe lesions are more likely to develop left congestive heart failure or infective endocarditis, presumably because they live long enough to develop late major complications of subaortic stenosis.
Open surgical correction of subaortic stenosis has not been shown to improve survival in dogs, with a report of sudden death occurring even after apparently successful surgery. When comparing balloon valvuloplasty to atenolol for treatment of subaortic stenosis, there was no evidence of surgical benefit over medical management.
Screening of puppies may be useful in estimating the risk of their developing this defect.
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