What is Ejection Fraction in Heart Failure
Ejection fraction (EF) is the percentage of blood ejected from the left ventricle with each heartbeat, calculated as stroke volume divided by end-diastolic volume, and serves as the primary metric for classifying heart failure types and guiding treatment decisions. 1
Definition and Measurement
EF represents the proportion of blood pumped out of the left ventricle during systolic contraction. 1 It is fundamentally determined by the end-diastolic volume of the ventricular chamber—a dilated heart typically has a lower EF. 1
Classification System Based on EF
The 2022 AHA/ACC/HFSA guidelines establish specific EF thresholds that define distinct heart failure phenotypes: 1
- HFrEF (Heart Failure with Reduced EF): LVEF ≤40% 1
- HFmrEF (Heart Failure with Mildly Reduced EF): LVEF 41-49% 1
- HFpEF (Heart Failure with Preserved EF): LVEF ≥50% 1
- HFimpEF (Heart Failure with Improved EF): Previous LVEF ≤40% with follow-up measurement >40% 1
Clinical Significance
EF classification is critical because it determines prognosis, treatment response, and eligibility for specific therapies. 1 Randomized controlled trials demonstrating survival benefit have predominantly enrolled patients with LVEF ≤35% or ≤40%, and evidence-based therapies are most robust for HFrEF. 1
Key Clinical Implications:
- Treatment selection: Most guideline-directed medical therapies with proven mortality benefit apply specifically to HFrEF 1
- Prognostic value: Lower EF generally correlates with worse outcomes, though this relationship weakens above 45% 2
- Trial enrollment: Clinical trials historically select patients based on EF thresholds 1
Diagnostic Requirements Beyond EF
For HFmrEF and HFpEF, EF measurement alone is insufficient for diagnosis—additional objective evidence of cardiac dysfunction is required. 1 This includes:
- Elevated natriuretic peptides (BNP/NT-proBNP) 1
- Evidence of increased LV filling pressures at rest or with provocation (exercise, fluid challenge) 1
- Structural abnormalities: left atrial enlargement, increased LV mass, or elevated E/e' ratio ≥15 1
Dynamic Nature and Trajectory
EF is not static—it changes over time based on treatment, disease progression, and underlying etiology. 1 Patients with HFmrEF typically exist on a dynamic trajectory, either improving from HFrEF or deteriorating toward it. 1 A single EF measurement at one time point may be inadequate; the trajectory over time is clinically important. 1
Important Caveats:
- Measurement variability: EF reproducibility is poor, particularly when values exceed 45% 2
- Treatment withdrawal risk: EF can decrease after stopping medications in patients who improved to normal range with guideline-directed medical therapy 1
- Continued treatment necessity: Even if EF improves to >40%, patients should continue HFrEF therapies as HFimpEF 1
Limitations of EF-Based Classification
While EF remains the dominant classification parameter, recent evidence suggests limitations in relying solely on arbitrary cutpoints. 2, 3 EF is a continuous variable, and cutpoints are often based on historical trial enrollment criteria rather than pure physiology. 3 The prognostic and diagnostic value of EF diminishes above 45%, with no clear relationship between EF and severity of cardiac dysfunction or outcomes at higher values. 2
Despite these limitations, EF classification remains essential for clinical practice because it guides treatment eligibility and has been the basis for virtually all major heart failure trials. 1