Isolated Supravalvar Aortic Stenosis Without William's Syndrome.

Supravalvular aortic stenosis, characterized by narrowing of the ascending aorta above the valve, is the least common form of left ventricular outflow tract obstruction and is usually associated with William's syndrome. We present a case of a 27-year-old male with isolated supravalvar aortic stenosis (SVAS) presenting with heart failure. This case underscores the fact that in rare cases sporadic SVAS can occur in isolation without the classic findings of William's syndrome and highlighting the importance of integration of clinical and echocardiographic recognition for definitive management.

INTRODUCTION

Left ventricular outflow tract obstructions (LVOTOs) encompass a series of stenotic lesions starting in the anatomic LVOT and may involve parts of the aorta. Obstruction may be subvalvar, valvar, or supravalvar and are usually with associated congenital anomalies. These lesions impose increased afterload on the left ventricle and can result in hypertrophy and eventual dilatation and failure of the left ventricle.[1] Supravalvar aortic stenosis (SVAS) is the rarest of all forms of LVOTO, which has been reported to be associated with William's syndrome.[2] The true incidence of isolated SVAS is unknown.[3]

CASE REPORT

A 27-year-old Filipino male began to experience easy fatigability accompanied by dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea 1-year prior to consultation. There was a progression of symptoms and patient eventually sought consult and was said to have valvular heart disease. He was advised further work up and referral to our institution. Past medical history and family history were unremarkable. Physical examination showed he had intact mentation and was coherent. Blood pressure was 100/70 with a regular heart rate of 73 beats/min. The patient did not have any elfin facies or other facial abnormalities. Cardiac findings showed a dynamic precordium, a displaced apex beat at the 6th intercostal space left midclavicular line, with LV heave. A harsh 3/6 systolic murmur is heard at the 2nd right intercostal space which also radiates to the carotid area. Electrolytes and renal function were normal. A diagnostic evaluation showed left ventricular hypertrophy by voltage criteria as well as an enlarged heart with left ventricular prominence on chest X-ray. Serum calcium and other blood chemistries were normal. Transthoracic echocardiogram revealed a supravalvar aortic membrane with severe obstruction. Peak systolic pressure gradient was 135 mmHg [Figure 1]. There was also concentric left ventricular hypertrophy with severe hypokinesia and depressed global systolic function (29% by Simpson's) and Doppler evidence of Grade III diastolic dysfunction. Preoperative transesophageal echo (TEE) showed a linear echogenic density just above the aortic valve confirming the finding of SVAS. The aortic valve cusps are also thickened and fused indicating the presence of a concomitant valvar aortic stenosis [Figure 2]. The patient eventually underwent aortic valve replacement, excision of the supravalvar membrane and aortic root dilatation with aortotomy and pericardial patch augmentation. There was a note of severe aortic stenosis with a fusion of the aortic valve cusps and calcification of the aortic annulus intraoperatively. Postoperative TEE revealed an effective orifice area of Effective orifice area of 1.59 cm2 by continuity equation, the mean gradient of 5.4 mmHg; peak instantaneous gradient of 10 mmHg. The patient was discharged improved and stable. Follow-up echocardiogram showed a normally functioning prosthetic valve with improvement of wall motion compared to previous study as well as improvement of ejection fraction from 29% to 50% with Grade II diastolic dysfunction. He is presently maintained on anticoagulation with good functional capacity.

Figure 1

Transthoracic echocardiogram showing supravalvar aortic stenosis. Note the discrete membrane above the aortic valve (yellow encircled). The sinotubular junction and ascending aorta were normal. Continuous waveform Doppler showed a peak systolic pressure gradient of 135 mmHg

Figure 2

Transesophageal echocardiogram showed a linear echogenic density above the aortic valve with +1 aortic regurgitation (blue arrow, left). The aortic valve cusps are thickened with restriction of motion of the noncoronary cusp and right coronary cusp creating an echo-free space, indicating a concomitant valvular aortic stenosis (right)

DISCUSSION

SVAS is by far the rarest form of LVOTO, reportedly accounting for 0.6 up to 6% of cases although the true incidence is unknown.[13] It usually occurs as a feature of William's syndrome,[2] which is characterized by elfin facies, mental retardation, and hypercalcemia. A familial form without features of William's syndrome inherited in an autosomal dominant pattern and rarely in sporadic patients without a family history. Genetic studies have demonstrated that the forms of supravalvar AS are caused either by mutations or deletion of the elastin gene located on chromosome 7q11.23. Histologic studies have shown diseased media with an increased collagen content and reduced elastic tissue in the form of broken and disorganized elastin (elastin arteriopathy). The reported incidence of William's syndrome is 1/20000 to 1/50000 and can occur either in an autosomal dominant or sporadic form.[3] Our patient did not have features of this disorder and family history was unremarkable, so he probably had the sporadic form. There are three recognized morphologic varieties, the most common type being the hourglass (segmental) variety which occurs in some 66% of cases, and in which there is gross thickening of the media often associated with intimal fibrous hyperplasia. Next in frequency is the hypoplastic type seen in approximately 21% of cases. The most unusual variety is the membranous type (13% of cases) consisting of a simple fibrous membrane with a single perforation allowing for blood flow.[4] Clinical manifestations related to supravalvar disease are due to the left ventricular outflow obstruction. Coronary perfusion is impaired not only by the systolic stress brought about by the hypertrophy but also with diastole being impeded by the supravalvar membrane, which may lead to further subendocardial ischemia, afterload mismatch, and eventually left ventricular dysfunction. Aortic insufficiency, angina, and congestive heart failure can occur.[5]

The congenital form of SVAS (without William's syndrome) has been reported to be associated with other abnormalities such as coarctation of the aorta, patent ductus arteriosus, atrial septal defect, ventricular septal defect, atrial septal defect, and mitral valve abnormalities (Barlow syndrome). Other findings have been described including pulmonary and coronary artery involvement.[6] The incidence of isolated SVAS is unknown, but it is believed that this form is rarer than the one associated with William's syndrome.[7] A multicenter retrospective study analyzed the outcomes of 113 patients with SVAS, 45% did not have William's syndrome. NYHA Class II or greater, mitral valve involvement and a gradient of >50 mmHg were predictors of operative and postoperative events.[8] Another interesting aspect of our case is the presence of a concomitant valvar aortic stenosis. In the study by Greutmann et al., 22 of the 51 patients without William's syndrome had other concomitant lesions including aortic valve stenosis in 14 of the 22 patients.[8] The supravalvar portion of the disease has profound effects on the architecture and function of the aortic valve itself.[9] This emphasizes the advantage of TEE for superior visualization of the aortic valve and provide further detail which can be missed on transthoracic echo that may have implications in surgical management. Definitive therapy consists of surgical correction of the obstruction. The postoperative outcomes of patients without any other concomitant genetic or congenital abnormalitis are good.[10]

CONCLUSIONS

SVAS is the rarest form of LVOTO that is frequently associated with William's syndrome and rarely in an isolated, sporadic form. Clinical and echocardiographic recognition is of utmost importance for treatment and improvement of outcomes.

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Conflicts of interest

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