Although subaortic stenosis is the second most-common form of LV outflow tract obstruction, it is predominantly found in children or adolescents [4
]. Subaortic stenosis is strongly associated with other congenital heart defects [6
]; however, subaortic stenosis in association with TOF, especially in women, is extremely rare. According to a Medline database review of the last 30 years, only 11 patients were reported to have had both TOF and subaortic stenosis. Furthermore, all were diagnosed in childhood or adolescence (< 20 years of age) with two exceptions [5
]. The present case is peculiar in that subaortic stenosis manifested more than 20 years after the initial TOF surgical correction.
The cause of subaortic stenosis in the present case remains uncertain. However, both congenital and acquired forms were suggested. Although we could not definitively say that the subaortic stenosis in the present case was acquired, we consider it an acquired or progressive form given the long interval (> 20 years) before echocardiographic confirmation. Thomas and Foster [5
] suggested that acquired subaortic stenosis can develop gradually due to hemodynamic disturbances derived from coexisting lesions or after surgical correction. Moreover, the mass-like mobile structure observed on transesophageal echocardiography could be regarded as a degenerative byproduct of flow convergence induced by the subaortic membrane, further supporting the concept of an acquired or progressive form of the disease [9
Discrete subaortic stenosis is well-known to be linked to important complications, such as bacterial endocarditis and significant aortic regurgitation. Flow turbulence distal to the obstructing subaortic membrane plays a crucial role in progressive damage to the aortic valve with resultant thickening of its leaflets and regurgitation. The secondary jet lesion also predisposes the patient to bacterial endocarditis [4
]. In this context, early detection of subaortic stenosis is of clinical relevance and should be pursued aggressively. In particular, patients with surgically corrected TOF tend to be misinterpreted as having only residual RV outflow obstruction without consideration of the LV outflow tract lesion. Transthoracic and transesophageal echocardiography can assist differentiation of the RV from the LV outflow tract obstruction. Therefore, periodic performance of echocardiography should be kept in mind during follow-up of patients with surgically corrected TOF.