Abstract Body (Do not enter title and authors here): Background: Surgical myectomy (SM) is recommended to relieve left ventricular outflow tract obstruction (LVOTO) in symptomatic obstructive hypertrophic cardiomyopathy (oHCM) patients who are intolerant to maximal background medical therapy. However, outcomes of such patients, if operated earlier at the onset of symptoms, remains uncertain.

Objective: We sought to assess whether an earlier SM is associated with improved longer-term outcomes in oHCM.

Methods: Between 1/2002 and 12/2018, out of 7954 HCM patients, 2904 with oHCM underwent SM following a thorough clinical evaluation at a large tertiary referral center. Clinical and imaging characteristics were recorded. Time to SM, cardiac transplantation, appropriate defibrillator discharge during follow-up were recorded. Primary outcome was a composite of mortality, appropriate internal cardioverter defibrillator (ICD) discharge or cardiac transplantation.

Results: Baseline characteristics, divided based on New York Heart Association (NYHA) class I (n=328), II (n=1062) and III (n=1514) are shown in Figure 1. Patients undergoing SM after progressing to NYHA Class III/IV were older, more likely to be women, had significantly higher proportion of comorbidities and background HCM therapy, poorer functional capacity, along with a higher proportion of concomitant mitral regurgitation vs. those who were in NYHA Class I/II. Overall, in-hospital mortality was observed in 9 (0.3%) patients. At a mean follow-up of 12±5 years, there were 672 composite events (635 deaths, 9 cardiac transplants and 47 appropriate ICD discharges). Despite a much longer time from initial evaluation to SM, patients in NYHA Class III/IV at initial presentation had significantly higher proportion (similar to age-gender matched normal US population) of adjusted longer-term composite events vs. NYHA Class II and I, respectively (387 [26%] vs. 216 [20%] vs. 69 [21%], p<0.001, Figure 2).

Conclusions: In a large sample of oHCM patients, evaluated at a high-volume tertiary care center, SM performed earlier closer to the time of symptom onset have significantly better long-term freedom from composite events vs. those who underwent SM after developing advanced symptoms. Better strategies for earlier symptom recognition, especially in women with oHCM, need to be developed. This would potentially enable early institution of appropriate therapies to relieve LVOTO.