Systolic Heart Failure (Reduced Ejection Fraction)

Systolic heart failure, now usually termed heart failure with reduced ejection fraction (HFrEF), is the phenotype in which the left ventricle contracts weakly, lowering the fraction of blood it ejects with each beat (typically a left ventricular ejection fraction of 40% or less). It is the form of heart failure for which the largest body of disease-modifying trial evidence exists.

Definition

Heart failure with reduced ejection fraction is a heart failure syndrome accompanied by a left ventricular ejection fraction at or below roughly 40%, reflecting impaired systolic (contractile) performance of the left ventricle.

Scope

This topic covers the definition of HFrEF by ejection fraction, the contractile and remodelling abnormalities that characterise it, the neurohormonal model that explains its progression, and how it is distinguished from the preserved-ejection-fraction phenotype. It is an educational reference and does not provide individualised treatment guidance.

Core questions

• What ejection-fraction threshold defines reduced ejection fraction?
• Why does impaired contractility lead to congestion and reduced perfusion?
• How does neurohormonal activation drive progressive ventricular remodelling in HFrEF?
• What distinguishes HFrEF from heart failure with preserved ejection fraction?

Key concepts

• Left ventricular ejection fraction at or below 40%
• Impaired systolic contractility
• Adverse ventricular remodelling
• Neurohormonal activation
• Reverse remodelling with neurohormonal antagonism

Key theories

Neurohormonal model of HFrEF progression

Reduced contractility lowers effective output and activates the sympathetic and renin-angiotensin-aldosterone systems; chronic activation drives adverse remodelling and progression, which is why antagonising these pathways modifies the disease course in HFrEF.

Mechanisms

In HFrEF the left ventricle's contractile performance is impaired, so a smaller fraction of end-diastolic volume is ejected. The fall in effective cardiac output activates compensatory sympathetic and renin-angiotensin-aldosterone responses that initially support blood pressure and perfusion but, sustained, promote eccentric remodelling, fibrosis, and chamber dilation. This maladaptive cycle, articulated by the neurohormonal hypothesis, explains why interfering with these pathways can slow or partially reverse the structural decline.

Clinical relevance

HFrEF is the heart-failure phenotype with the most robust trial evidence for disease-modifying therapy, and its ejection-fraction definition organises how cardiology classifies and studies the syndrome. This entry describes the phenotype conceptually and is not a guide to individual diagnosis or therapy.

Epidemiology

HFrEF accounts for a large share of heart failure cases, with the balance between reduced and preserved phenotypes varying by age and population. It has historically been the focus of landmark therapeutic trials, which shapes the evidence base summarised in society guidelines.

Evidence & guidelines

Contemporary ESC and AHA/ACC/HFSA guidelines define HFrEF by ejection fraction and synthesise the trial evidence underlying its classification; landmark randomised trials such as PARADIGM-HF illustrate the neurohormonal rationale. These are cited as reference and classification sources, not as treatment instructions.

History

The conception of systolic heart failure evolved from a haemodynamic view toward the neurohormonal model in the late twentieth century. Successive randomised trials targeting the renin-angiotensin-aldosterone and sympathetic systems — culminating in studies such as PARADIGM-HF — both confirmed and refined this model and established reduced ejection fraction as the phenotype most amenable to disease modification.

Key figures

• Milton Packer
• John McMurray
• Theresa McDonagh

Seminal works

• packer-1992
• mcmurray-2014-paradigm
• mcdonagh-2021-esc

Frequently asked questions

What ejection fraction counts as 'reduced'?

Guidelines generally define heart failure with reduced ejection fraction as a left ventricular ejection fraction of 40% or less, distinguishing it from the mildly reduced (41-49%) and preserved (50% or above) categories.

Why is HFrEF the most-studied form of heart failure?

Because its mechanism — impaired contractility with neurohormonal activation — provided clear therapeutic targets, HFrEF has been the subject of the largest randomised trials, giving it the strongest disease-modifying evidence base.