Congenital Muscular Mitral-Aortic Discontinuity Identified in Patients With Obstructive Hypertrophic Cardiomyopathy

Abstract

BackgroundThe mitral valve is often structurally abnormal in hypertrophic cardiomyopathy (HCM). However, the mechanisms responsible for these abnormalities remain controversial. In 2016 we identified, at myectomy, muscular mitral-aortic discontinuity in 5 young patients with obstructive HCM. ObjectivesThis study sought to confirm our preliminary findings and assess the prevalence of muscular mitral-aortic discontinuity in obstructive HCM. MethodsAt our center, from January 2017 to April 2018, the area between the anterior mitral leaflet and aortic valve was inspected at myectomy in 106 consecutive patients with HCM. ResultsMuscular mitral-aortic discontinuity was identified in 28 (26%) patients and was significantly more common in younger than older patients (age 39 ± 13 years vs. 58 ± 11 years; p < 0.001). Muscular discontinuity was present in each of 6 patients aged <30 years but only 1 (2.7%) of 37 aged ≥60 years. Pathogenic sarcomere mutations were identified in 22 (79%) of 28 patients with and 24 (31%) of 78 without discontinuity (p < 0.001) and were associated with discontinuity independently of age (p = 0.021). Discontinuity mean length was 7.3 mm and was inversely related to age (p = 0.022). At echocardiography, the anterior mitral leaflet was longer in patients with than those without discontinuity (34 ± 4 mm vs. 29 ± 5 mm; p < 0.001). ConclusionsWe report, for the first time, muscular mitral-aortic discontinuity in HCM. At myectomy, a long muscular discontinuity displaced the anterior mitral leaflet toward the apex in most young patients, was significantly associated with sarcomere mutations independent of age, and was extremely uncommon in older patients. These findings suggest that a long muscular mitral-aortic discontinuity could predispose to the development of outflow obstruction in young patients with sarcomere mutations.