European Journal of Heart Failure (2018) 20, 433–435 VIEWPOINT doi:10.1002/ejhf.1116 Left ventricular ejection fraction in heart failure: a clinician’s perspective about a dynamic and imperfect parameter, though still convenient and a cornerstone for patient classifcation and management Josep Lupón 1,2,3 * and Antoni Bayés-Genís 1,2,3 1 Heart Failure Unit and Cardiology Service, Hospital Universitari Germans Trias i Pujol, Badalona, Barcelona, Spain; 2 Department of Medicine, Universitat Autònoma de Barcelona, Barcelona, Spain; and 3 CIBER Cardiovascular, Instituto de Salud Carlos III, Madrid, Spain ‘Il meglio è nemico del bene’ (‘The better is enemy of the good’) Proverbi Italiani e Latini (Orlando Pescetti, 1603), popularized as ‘Le mieux est l’ennemi du bien’ by Voltaire (Dictionnaire philosophique, 1700; La Béguele, 1772) For decades, heart failure (HF) has been classifed based on left ventricular ejection fraction (LVEF), which is calculated as stroke volume (i.e. end-diastolic volume minus end-systolic vol- ume) divided by end-diastolic volume. Since these parameters are rather easy to understand and to obtain using various cardiac imag- ing techniques, LVEF is generally known and accepted by all physi- cians attending HF patients. However, LVEF has many acknowl- edged limitations, including technical issues in obtaining the images, data variability and poor reproducibility, variations among different imaging techniques, dependency on heart rate such that atrial fb- rillation and rapid ventricular response may lead to a falsely low LVEF, and reduced accuracy in patients with left bundle branch block or ventricular pacing due to pacemaker implantation. Addi- tionally, LVEF only provides a partial picture of patients with HF. Indeed, LVEF often shows inadequate correlation with functional capacity, and it does not provide accurate information regarding diastolic function. Moreover, even when only addressing left ven- tricular systolic dysfunction, LVEF may be less accurate than other echocardiographic measurements, such as longitudinal and global strain or speckle tracking. However, despite these issues, from the clinicians’ perspective (beyond aetiology, geometry, volumes, dias- tolic issues, etc.), LVEF remains the most convenient parameter and is a cornerstone in four areas of daily clinical work: (i) HF classifcation, (ii) HF prognosis assessment, (iii) HF treatment and *Corresponding author. Heart Failure Unit and Cardiology Service, Department of Medicine, U.A.B. Hospital Universitari Germans Trias i Pujol, Carretera del Canyet s/n, 08916 Badalona, Spain. Tel: +34 93 4978915, Fax: +34 93 4978939, Email: jlupon.germanstrias@gencat.cat .......................................................................................... management, and (iv) HF monitoring. Below, we will discuss each of these aspects. Classically, two types of HF have been acknowledged relative to LVEF (or left ventricular performance): HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). While normal LVEF is generally considered to be >50%, 1 both conditions have been arbitrary defned with regard to the cut-off points used to delineate HFrEF and HFpEF. Most randomized controlled trials aiming to establish optimal medical treatment defne reduced LVEF as ≤35–40%, 2 while most studies investigating HFpEF enrol patients having HF with an LVEF of >40–45% and overall HFpEF is variably defned by an LVEF of >40%, >45%, >50%, or ≥55%. 2 In the 2013 American College of Cardiology/American Heart Association guidelines, 2 HFrEF is defned as a clinical diagnosis of HF with an LVEF of ≤40%, HFpEF is defned by an LVEF of ≥50%, while an LVEF of 41 –49% is considered borderline. The 2016 European Society of Cardiology guidelines 1 present a new HF classifcation including a third category—HF with mid-range ejection fraction (HFmrEF), defned as an LVEF of 40–49%—which replaces the previously designated ‘grey zone’ or borderline cate- gory. This third group was created to boost investigation of these patients, who were poorly represented in clinical trials of both HFrEF and HFpEF. The emergence of HFmrEF led to a plethora of reports providing insight into the clinical characteristics and outcomes among these patients, with controversial results. When investigating patients with HFmrEF, some studies describe clini- cal characteristics similar to those of patients with HFrEF, 3 while other studies report clinical characteristics and prognosis similar to HFpEF. 4 © 2017 The Authors European Journal of Heart Failure © 2017 European Society of Cardiology