LVOT obstruction and severe aortic regurgitation caused by anterolateral muscle bundle of the left ventricle: The embryologic remnant of the bulbo-atrioventricular flange
Altibi A, Jebbawi LA, and Patel BD. LVOT obstruction and severe aortic regurgitation caused by anterolateral muscle bundle of the left ventricle: The embryologic remnant of the bulbo-atrioventricular flange. Journal of the American College of Cardiology 2020; 75(11):2972.
J Am Coll Cardiol
Background An anterolateral muscle bundle runs along the wall of the left ventricular outflow tract (LVOT) and may extend up to the level of aortic valve (AV). The muscle bundle may occasionally bulge into the LVOT without causing significant obstruction. Case A 53 year old female patient presented with worsening chest discomfort and exercise intolerance. Initial TTE showed ejection fraction of 56% and AV area (AVA) of 0.66 cm2 indicative of severe stenosis, but with peak gradient of 29 mmHg. However, TEE showed very mild aortic stenosis with 3D aortic valve planimetry measuring 1.8 cm2. TEE showed hypertrophied basal septum (thick membrane connecting mitral leaflet with AV). The thickened septum was causing severe LVOT obstruction (LVOT area was 0.85 cm2) and a tertiary cord was attached to its base. The septum attaches to the right coronary cusp causing restriction and severe regurgitation. Cardiac catheterization showed severe stenosis at the LVOT. Decision-making The findings are indicative for anterolateral muscle bundle causing LVOT obstruction, rather than primary AV pathology. Hence, patient underwent septal myectomy, resection of subaortic membrane, and AV repair successfully. Post-myomectomy TTE showed minimal stenosis with AVA of 1.34 cm2. Conclusion LVOT obstruction can be caused by hypertrophied anterolateral muscle bundle in the absence of primary valvular pathology. Proper diagnosis is crucial since resection of the subaortic membrane and septal myectomy is the treatment of choice.