Sex differences in surgically treated left-sided infective endocarditis: results from the international, prospective, multicentre BESOS study

OBJECTIVES: We aimed to describe sex differences in clinical characteristics and 30-day mortality in a large contemporary cohort of patients undergoing surgery for left-sided infective endocarditis (IE). METHODS: The international Barcelona Endocarditis Surgery Outcome Score registry included consecutive patients undergoing surgery for active left-sided IE across 55 centres in 19 countries in 2025. Clinical characteristics and outcomes were prospectively collected. The primary outcome was 30-day mortality. Propensity score 1:1 nearest-neighbour matching (PSM) was performed to generate balanced male and female cohorts. Cox proportional hazards models were used to assess the association between sex and mortality, with adjustment for age, comorbidities and frailty, IE characteristics, and preoperative severity. RESULTS: Among 1085 patients undergoing surgery for left-sided IE (median age 65 years, interquartile range 53-73), 239 (22%) were women. Men and women had a similar burden of cardiovascular risk factors and comorbidities, although women exhibited greater frailty (Clinical Frailty Scale ≥7: 22/236 [9%] vs. 36/826 [4%]; p 0.01). Women more frequently presented with isolated mitral valve involvement (116/238 [49%] vs. 238/845 [29%]) and staphylococcal aetiology (86/239 [36%] vs. 218/846 [26%]; p 0.03). PSM identified 225 balanced male-female pairs. Thirty-day mortality was significantly higher in women than in men in both the overall cohort (49/239 [21%] vs. 87/846 [10%]; p <0.01) and the matched cohort (45/225 [20%] vs. 28/225 [12%]; p 0.02). Female sex remained associated with increased 30-day mortality after adjustment (hazard ratio, 1.58; 95% confidence interval [CI], 1.02-2.45; p 0.04). CONCLUSIONS: In this large contemporary multinational cohort of patients undergoing surgery for left-sided IE, female sex was independently associated with higher 30-day mortality. The persistence of this association after PSM and multivariable adjustment suggests that the excess risk in women is not fully explained by differences in baseline characteristics, disease presentation, or preoperative severity, highlighting the need to better understand sex-related disparities in surgical IE outcomes.