Trial characteristics associated with under-enrolment of females in randomized controlled trials of heart failure with reduced ejection fraction: a systematic review

Aims: To evaluate temporal trends in the enrolment of females in randomized controlled trials (RCTs) of heart failure with reduced ejection fraction (HFrEF) published in high-impact journals, and assess RCT characteristics associated with under-enrolment.

Methods and results: We searched MEDLINE, EMBASE and CINAHL for studies published from January 2000 to May 2019 in journals with impact factor ≥10. We included RCTs that recruited adults with HFrEF. We used a 20% threshold below the sex distribution of HFrEF to define under-enrolment. We used multivariable logistic regression to assess trial characteristics independently associated with under-enrolment. We included 317 RCTs. Among the 183 097 participants, mean (standard deviation) age was 63.0 (7.0) years and 25.5% were female. Females were under-enrolled in 71.6% [95% confidence interval (CI) 66.6-76.6%] of the RCTs; enrolment did not increase significantly between 2000-2019. Sex-related eligibility criteria [odds ratio (OR) 2.05, 95% CI 1.01-4.16; P = 0.046]; recruitment in ambulatory settings (OR 2.56, 95% CI 1.37-4.81; P = 0.003); trial coordination in North America (OR 4.44, 95% CI 1.09-18.07; P = 0.037), Europe (OR 6.79, 95% CI 1.63-27.39; P = 0.018) and Asia (OR 9.33, 95% CI 1.40-12.40; P = 0.033); drug (OR 1.76, 95% CI 1.96-7.36; P < 0.001) and device/surgical interventions (OR 1.69, 95% CI 1.16-9.43; P = 0.002); and men in first and last authorship position (OR 1.32, 95% CI 1.12-3.54; P = 0.047) were associated with under-enrolment of females.

Conclusions: Females were under-enrolled relative to disease distribution in a majority of high-impact HFrEF RCTs, with no change in temporal trends between 2000 and 2019. Trial characteristics and gender of trial leaders were associated with under-enrolment.