**9. Recurrent left ventricular outflow tract obstruction after septal myectomy**

 With complete and proper septal myectomy ( **Figure 15** ), recurrence is quite low, especially in adults. As discussed previously, anatomic causes of recurrence such as mitral subvalvular abnormalities (anomalous papillary muscles, and anomalous chordae) should be ruled out during the initial myectomy to avoid reoperation or persistence/recurrence of symptoms.

 Other possible etiology includes unidentified midventricular obstruction which is being unmasked by the initial subaortic resection. Muscle growth is rare to occur in adults and is most likely to occur in those with congenital subaortic stenosis.

 The following mechanisms were identified in more than 50 patients with redo myectomy: limited initial myectomy, midventricular obstruction, and anomalous papillary muscles [ 24 ]. The repeat septal myectomy remains safe and feasible and should be the main treatment for those with recurrent/persistent LVOT gradient after initial limited resection.

 **Figure 15.**

 *Intraoperative tracing after a complete myectomy showing no resting gradient between the left ventricle and the aorta with negative Brockenbrough-Braunwald-maneuver.* 
