In most cases of postoperative LVOT obstruction in patients such as ours, such obstruction results from the protrusion of a high-profile prosthetic valve into the LVOT or from abnormal subvalvular positioning of the prosthesis. If the prosthesis is not oriented properly, a strut may obstruct the outflow tract.
In addition to the fixed type of LVOT obstruction, transient or dynamic obstruction may occur after MVR. If there is a narrowed mitral–aortic angle after MVR, transient LVOT obstruction may occur due to a thickened interventricular septum, systolic anterior motion of the anterior mitral leaflet, the reduction of LV dimensions, a hypercontractile left ventricle, or atrial fibrillation.4–6 In our patient, in the setting of a mild LVOT obstruction due to the prosthesis and its abnormal position, the obstruction might have been worsened by preload reduction secondary to atrial fibrillation and diuretics or by hypercontractile cardiac function as a result of digoxin therapy.
This case illustrates the pharmacologic attenuation of dynamic LVOT obstruction after bioprosthetic MVR. If the obstruction first occurs postoperatively, as happened with our patient, appropriate medication may improve the cardiac status, and reoperation may be avoided. Our patient was successfully treated with a β-blocker after discontinuation of the digoxin.
Our patient had undergone MVR with a high-profile bioprosthesis and preservation of the posterior subvalvular apparatus. Preservation of the subvalvular apparatus during MVR preserves LV function and reduces the risk of LV rupture.7–9 However, previous reports have shown that complete preservation of the anterior leaflet after prosthetic MVR harbors the potential for LVOT obstruction, which most frequently occurs after the insertion of a high-profile bioprosthesis.1,3,10 In patients who have isolated mitral stenosis and a small LV cavity, low-profile prostheses are recommended to avoid myocardial impingement and LVOT obstruction that can result from use of a high-profile valve. In our patient, however, echocardiography revealed neither septal hypertrophy nor a small LV cavity. The posterior leaflet was retained at MVR, and LVOT obstruction developed.
Regardless of whether the native leaflets are removed, mitral valve replacement with a high-profile valve frequently causes LVOT obstruction. In addition, correct orientation of high-profile bioprostheses is mandatory.