CHAPTER SUMMARY AND CENTRAL ILLUSTRATION
This chapter describes the presentation, diagnosis, and management of congenital left heart obstructive lesions, a series of anatomic stenotic lesions from the left atrium extending to the descending thoracic aorta (see Fuster and Hurst's Central Illustration). Obstruction may be in the left atrium, at the level of the aortic or mitral valve (subvalvar, valvar, or supravalvar), in the ascending aorta, transverse aortic arch, or in the descending thoracic aorta. These left heart obstructive lesions may present either in isolation or in association with other left-sided lesions. Based on their location, these lesions may cause impairment in valvular function (either aortic or mitral) or may impose increased afterload on the left ventricle and, if severe and untreated, may result in hypertrophy and dysfunction of the left ventricle. Cardiac imaging is essential for diagnosis, management, and long-term follow-up, and it increasingly plays a role in understanding the physiologic changes of left-sided obstructive lesions and the timing for intervention. Treatment is based on the underlying left heart obstructive lesion and may involve either transcatheter or directed surgical repair.
eFig 68-01 Chapter 68: Left Heart Obstructive Lesions
Subaortic stenosis is defined as narrowing of the left ventricular outflow tract. It results in 8% to 20% of left ventricular outflow obstruction.1,2 It is discrete in 90% of cases. In the remainder, the left ventricular outflow tract is diffusely hypoplastic and tunnel-shaped.3 In discrete forms, the membrane can be circular or crescent-shaped, and usually made of a nondistensible fibromuscular shelf. The membrane may encroach onto the underside of the aortic valve or the ventricular aspect of the anterior mitral valve leaflet, causing leaflet distortion and secondary regurgitation4 (Figs. 68–1 and 68–2).
Transthoracic echocardiography: apical five chamber image. Discrete subaortic membrane noted in the left ventricular outflow tract (see arrow).
Subaortic stenosis: different presentations. (A) Isolated geometry. (B) Involvement with the aortic valve. (C) Involvement with the mitral valve.
The etiology of subaortic stenosis is uncertain. Some have proposed that it is related to incomplete absorption of the subaortic infundibulum,5 but this is less likely given that it is usually not present in infants. There may be an underlying genetic association given that it can cluster in families.6 Most likely, the cause is related to change in the flow dynamics of the left ventricular outflow tract. Subaortic membranes are associated with steeper aorto-septal angles, the angle between the plane of the interventricular septum, and midline of the aortic valve. Kleinert et al. found that 68% of patients ...