Latent outflow tract obstruction in hypertrophic cardiomyopathy: Clinical characteristics and outcomes of septal myectomy

Objective: This investigation analyzed clinical characteristics of patients with hypertrophic cardiomyopathy (HCM) and latent left ventricular outflow tract (LVOT) and outcomes following septal myectomy. Methods: We reviewed patients with HCM and LVOT obstruction undergoing septal myectomy from 2001 to 2016 at our center. Follow-up data on functional status were obtained through mailed survey questionnaires. Results: There were 629 (31.8%) patients with latent obstruction (resting LVOT gradient <30 mm Hg, provoked gradient >30 mm Hg) among 1981 patients undergoing septal myectomy. Patients with latent obstruction were more likely to be male (65.7% vs 51.8%, P <. 001), but there were no important differences in other clinical characteristics. The New York Heart Association functional classes and measured/predicted maximal oxygen consumption (62 [51, 72] vs 60 [48, 72], P =. 158) in cardiopulmonary exercise tests were comparable between the 2 groups. Patients with latent obstruction had both lower septal thickness and lower posterior wall thickness. Median intraoperative provoked pressure gradient decreased from 96 (68, 126) mm Hg to 0 (0, 6) mm Hg after myectomy (P <. 001). There was no difference in early (<30 days) deaths (3/629 vs 5/1352, P =. 726) and long-term survival between patients with latent obstruction and resting obstruction. In follow-up, both general health status and New York Heart Association functional class were significantly improved following septal myectomy. Conclusions: Patients with HCM and latent LVOT obstruction generally have milder left ventricular hypertrophy but similarly impaired functional capacity compared to those with resting obstruction. Septal myectomy improves functional capacity and symptoms.