Breakthroughs in the treatment of heart failure with mildly reduced and preserved ejection fraction

Historically, only patients with a left ventricular ejection fraction (LVEF) of less than or equal to 40% were considered to have heart failure (HF). However, it was later found that patients could have elevated cardiac filling pressures and the stigmata of HF signs and symptoms with normal LVEF. This subset of patients has undergone multiple taxonomical variations and is now termed heart failure with preserved ejection fraction (HFpEF) with the lower limit of LVEF assigned as roughly ≥40%-50% in clinical trials and ≥50% in HF guidelines. Patients with LVEF 41%-49% did not clearly fit these designations but bear resemblance to both heart failure with reduced ejection fraction (HFrEF) and HFpEF. This cohort was initially assigned the term HFpEF (borderline), which has also undergone several modifications and is currently termed heart failure with mildly reduced ejection fraction (HFmrEF). Earlier landmark HF trials were heavily focused on patients with HFrEF. Only in the last 2 decades has there been an increasing focus on HFpEF with emergence of key drug therapies including sodium-glucose cotransport-2 inhibitors that have shown to improve outcomes across the whole LVEF spectrum. There is yet to be a focused clinical trial to determine therapeutic modalities for HFmrEF; most of the evidence has been extrapolated from subgroup analysis mostly from HFpEF trials. In this review, we provide an overview of the historical basis of HFpEF and HFmrEF and discuss key therapeutic advances in their management.