Incident Heart Failure With Mildly Reduced Ejection Fraction: Frequency, Characteristics, and Outcomes

Background: Heart failure (HF) with an ejection fraction (EF) of 41%–49% is recognized as HF with a mildly reduced EF (HFmrEF). However, existing knowledge of the HFmrEF phenotype is based on HF clinical trial and registry cohorts that may be limited by multiple forms of bias. Methods and Results: In a community-based, retrospective cohort study, adult residents of Olmsted County, Minnesota, with validated (Framingham criteria) incident HF from 2007 to 2015 were categorized by echocardiographic EF at first HF diagnosis. Among 2035 adults with incident HF, 12.5% had HFmrEF, 29.9% had HF with reduced EF (HFrEF), and 57.6% had HF with preserved EF (HFpEF). Mean age and sex varied by EF group, with HFmrEF (75.6 years, 45.3% female), HFrEF (70.9 years, 36.5% female), and HFpEF (76.9 years, 59.7% female). Most comorbid conditions were more common in HFmrEF vs HFrEF, but similar in HFmrEF and HFpEF. After a mean follow-up of 4.6 ± 3.5 years, adjusting for age, sex, and comorbidities, the risks of hospitalization and cardiovascular mortality did not differ by EF category. Of patients who began as HFmrEF, 26.9% declined to an EF of 40% or less and 44.8% improved to an EF of 50% or greater. Conclusions: In this community cohort of incident HF, 12.5% have HFmrEF. Clinical characteristics in HFmrEF resemble HFpEF more than HFrEF. Adjusted hospitalization and mortality risks did not vary by EF group. Patients with incident HFmrEF usually transitioned to a different EF category on follow-up.