lar mass, like tumors or vegetations, can pro- duce similar findings on echocardiography. However, these lesions more often originate from cardiac muscle (tumors), or build-up on the low-pressure side of a heart valve (vegeta- tions),3 and do not have a leaﬂet-like appear- ance. Subaortic membrane has a different appearance of a single, linear membrane in the LVOT. Surgical excision of the AMVT is required while repairing other congenital defects or if significant LVOT obstruction is present.2,7 In patients with TGA, either pre- or post-operative LVOT obstruction commonly occurs due to bicuspid or unicommissural pulmonary valve, fibrous ridge, obstructive muscular conus, malaligned outlet septum, bulging muscular septum, straddling mitral valve, anterior mitral valve rotation and AMVT.8 Table 1 shows the common types of obstruction with manage- ment options in patients with TGA.9,10 Yoshimura et al. reported 2 cases of AMVT associated with TGA. In one of these, release of the LVOT obstruction due to AMVT was neces- sary to perform the arterial switch operation.4 In the second patient, it was not possible to perform the arterial switch operation because the AMVT could not be resected completely through the pulmonary artery. It was felt that there is a high chance of overlooking the AMVT intra-operatively, especially if no pre- operative diagnosis is made. In their series of Type of LVOT obstruction Dynamic (septal shift due to pLV/pRV < 1) Pulmonary valve abnormalities (unequal cusp sizes, bicuspid, dysplasia, annular hypoplasia commissural fusion) Subvalvar ﬁbrous membrane Subvalvar ﬁbromuscular tunnel Table 1. Possible causes of LVOT obstruction and their management in TGA. Case Report Figure 1. Transthoracic echocardiogram in different views showing accessory mitral valve tissue attached to ventricular aspect of anterior mitral valve leaflet prolapsing into left ventricular outflow tract in systole (A, B, C arrowheads) in a post-Senning surgery patient. Figure 2. (A) Color Doppler echocardiogram showing severe turbulence in the left ventric- ular outflow tract. (B) Continuous wave Doppler examination showing severe left ventric- ular outflow tract obstruction with peak gradient of 79 mmHg and a mean gradient of 49 mmHg, in a patient with accessory mitral valve tissue. Associated lesions Management IVS/VSD (high pulmonary blood flow, SAM, tricuspid tissue hernia may contribute to gradient) IVS VSD IVS VSD IVS VSD VSD ASO usually relieves gradient by reversing pLV/pRV. Rare in isolation, usually part of complex LVOT obstruction in TGA with VSD. Not always obstructive in isolation. ASO may result in neo-aortic leak or root dilatation. Intraventricular rerouting (Rastelli or REV) is the method of choice in the majority of patients. Similar to subaortic membrane in concordant hearts. Usually resectable. ASO + resection. Often associated with hypoplastic pulmonary valve. Difﬁcult to relieve by resection. Rastelli/REV, Nikaidoh-Bex (aortic translocation), ASO, all options possible. Difﬁcult to relieve by resection. Nikaidoh-Bex or REV good option. Septal malalignment (deviation of outlet septum into LVOT) Accessory tricuspid valve tissue VSD Prolapses through VSD to cause LVOT obstruction. Usually resectable. ASO+resection. Accessory mitral valve tissue IVS Prolapses into LVOT. VSD Usually resectable. ASO+ Resection. Anomalous insertion of mitral valve VSD Difﬁcult to relieve by resection, even if septation is otherwise chordae or papillary muscle to outlet septum, possible. Various techniques such as Nikaidoh-Bex may be straddling tricuspid valve necessary or single ventricle approach if severe mitral valve abnormalities. Accessory endocardial cushion tissue relating VSD Prolapses into LVOT. to a VSD Usually resectable. ASO+ resection ASO, arterial switch operation; IVS, intact interventricular septum; SAM, systolic anterior motion of mitral valve; LV, left ventricle; LVOT, left ventricular outﬂow tract; pLV/ pRV, LV to right ventricle pressure gradient; VSD, ventricular septal defect; REV procedure, Reparation A L’etage Ventriculaire. [Heart International 2011; 6:e6] [page 19]