tetralogy of fallot ( tof ) accounts for approximately 5% to 7% of all cases of congenital heart disease . complications related to surgical repair of tof are clinically relevant and include pulmonary regurgitation , residual obstruction of the right ventricular ( rv ) outflow tract , rv systolic dysfunction , and arrhythmias . among these , residual rv outflow tract obstruction with accompanying pulmonary regurgitation is the most frequently reported sequela after initial surgical correction of tof . therefore , a systolic murmur that is audible over the base of the heart is frequently interpreted as a residual rv outflow tract lesion . however , this is not always true . we herein report a rare case of subaortic stenosis in association with a previous tof surgical repair that was not considered to be a differential diagnosis . discrete subaortic stenosis is generally thought of as a disease of children or young adults ( < 25 years of age ) and is thus rarely reported in subjects older than 25 years , particularly in association with tof . a 29-year - old woman presented for a routine check - up of surgically corrected congenital heart disease . at 7 years of age , she had undergone surgical repair of tof with excision of the infundibular stenosis and closure of a 10-mm ventricular septal defect . she had been asymptomatic until her first decade of life , and only a 5-year clinical follow - up had been performed after the operation . approximately 6 months prior to presentation , she began to feel exertional dyspnea that was progressively aggravated . on physical examination , she was alert and well - oriented . her blood pressure was 100/60 mmhg , pulse 60 beats / min , respiration rate 18/min , and body temperature 36.6. the left ventricular ( lv ) impulse was almost normal in location . on auscultation , a grade 3 of 6 mid- to late - systolic murmur was audible over the base of the heart and heard clearly on both sides of the sternum . routine blood examinations , including a complete blood count , chemistry panel , coagulation panel , and c - reactive protein level , were all within normal ranges . transthoracic and transesophageal echocardiograms both demonstrated severe subaortic stenosis due to a subvalvular membrane , on which a mobile mass - like structure that was suspicious of a vegetation was noted ( fig . there was a mild degree of tricuspid regurgitation , but no clinically significant obstruction of the rv outflow tract . the maximum velocity measured across the tricuspid valve was 2.8 m / sec , and thus the maximal pressure gradient was estimated to be 31.4 mmhg using the simplified bernoulli equation . due to the up to 20 mmhg pressure gradient across the pulmonary valve her rv was not dilated , and its systolic function was good . due to the suspicion of infective endocarditis despite the absence of clinical evidence , blood cultures were performed three times ; however , no pathogen was cultured . the patient underwent resection of the subaortic membrane and myomectomy of the lv outflow tract along with aortic valve commissurotomy . the membrane , with the exception of the noncoronary cusp area , was located beneath the aortic annulus ( i.e. , inverted u shape ) . the mobile mass - like structure described on transesophageal echocardiography was proven to be loose tissue attached to the subaortic membrane . although subaortic stenosis is the second most - common form of lv outflow tract obstruction , it is predominantly found in children or adolescents [ 4 - 8 ] . subaortic stenosis is strongly associated with other congenital heart defects ; however , subaortic stenosis in association with tof , especially in women , is extremely rare . according to a medline database review of the last 30 years furthermore , all were diagnosed in childhood or adolescence ( < 20 years of age ) with two exceptions . the present case is peculiar in that subaortic stenosis manifested more than 20 years after the initial tof surgical correction . 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   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 . 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 . in this context , 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 .
we herein report a rare case of subaortic stenosis in association with a previous tetralogy of fallot ( tof ) surgical repair , which was not taken into account as a differential diagnosis . 
 echocardiography plays a pivotal role in identification of this rare combination . 
 therefore , echocardiography should be performed periodically during follow - up of patients with surgically corrected tof . 
 given the clinical complications that can result from subaortic stenosis ( i.e. , aortic regurgitation and infective endocarditis ) , early and aggressive management of this rare combination should be performed .