What have we learned about heart failure with mid-range ejection fraction one year after its introduction?

The 2016 European Society of Cardiology heart failure guidelines introduced the term 'heart failure with mid-range ejection fraction' (HFmrEF) to refer to patients with heart failure and a mildly reduced ejection fraction of 40-49%. About 20% of heart failure patients fall in this category. One of the main reasons for the introduction of this category was to stimulate research into this grey area. This review aims to highlight the key findings that have been published so far. Firstly, HFmrEF more closely resembles heart failure with reduced (HFrEF) than preserved ejection fraction (HFpEF) with regard to ischaemic aetiology, which is more frequent in both HFmrEF and HFrEF compared to HFpEF. Secondly, changes in ejection fraction over time are common, and seem to be more important than baseline ejection fraction alone. Patients who progress from HFmrEF to HFrEF have a worse prognosis than those who remain stable or transition to HFpEF. Lastly, and perhaps most importantly, retrospective analyses from a randomized trial suggest that patients with HFmrEF seem to benefit from therapies that have shown to improve outcome in HFrEF, whereas no such benefit was seen in patients with HFpEF.