Defining HFrEF vs HFpEF: Key Differences
Heart failure with reduced ejection fraction (HFrEF) is defined as LVEF ≤40%, while heart failure with preserved ejection fraction (HFpEF) is defined as LVEF ≥50%, with these two entities representing fundamentally different pathophysiological processes that require distinct therapeutic approaches 1.
Classification by Ejection Fraction
The primary distinguishing feature is left ventricular ejection fraction:
- HFrEF: LVEF ≤40%
- HFmrEF (mildly reduced): LVEF 41-49%
- HFpEF: LVEF ≥50%
This classification matters because most randomized controlled trials demonstrating survival benefit have enrolled patients with LVEF ≤35-40%, making HFrEF the phenotype with the strongest evidence-based treatment options 1.
Pathophysiological Differences
HFrEF Mechanisms
HFrEF is characterized by impaired systolic function with eccentric remodeling (mass/volume ratio 0.47±0.15), driven by:
- Cardiomyocyte stretch and damage (markedly elevated BNP, pro-BNP, NT-proBNP, troponin-I)
- DNA binding transcription factor activity
- Cellular protein metabolism dysregulation
- Impaired nitric oxide biosynthesis 2, 3
HFpEF Mechanisms
HFpEF involves concentric remodeling (mass/volume ratio 0.68±0.16) with:
- Diastolic dysfunction (impaired LV relaxation, increased LV stiffness)
- Elevated LV filling pressures at rest or exertion
- Inflammation and cytokine response
- Extracellular matrix reorganization
- Systemic metabolic dysfunction 2, 3, 4
Importantly, HFpEF represents approximately 50% of all heart failure patients, with prevalence increasing due to aging populations and rising rates of obesity and diabetes 5.
Clinical Predictors and Risk Factors
Factors Predicting HFrEF
- Male sex
- Coronary heart disease (strongest predictor)
- Higher heart rate
- Higher total cholesterol
- Left bundle branch block
- Ischemic ECG changes
- Left ventricular hypertrophy
- Smoking
- Elevated troponin 6, 7, 8
Factors Predicting HFpEF
- Female sex (strong association)
- Older age (stronger than for HFrEF)
- Atrial fibrillation
- Higher body mass index/obesity
- Diabetes mellitus
- Valvular disease
- Increased urinary albumin excretion
- Elevated cystatin C 6, 7, 8
These clinical features can discriminate between HFrEF and HFpEF with good accuracy (c-statistic 0.75-0.78) 6.
Diagnostic Considerations
For HFpEF and HFmrEF, diagnosis requires not just symptoms and appropriate LVEF, but additional objective evidence of cardiac dysfunction 1. This includes:
- Elevated natriuretic peptides (though normal levels don't exclude HFpEF)
- Evidence of increased LV filling pressures (spontaneous or provokable)
- Structural cardiac abnormalities on imaging
This additional requirement improves diagnostic specificity, as HF symptoms are frequently nonspecific and overlap with other conditions 1.
Structural and Functional Differences
Both HF subtypes share:
- Lower exercise capacity
- Higher LV filling pressures (E/E', BNP, LA volumes)
- RV systolic dysfunction
- Myocardial fibrosis 3
However, HFrEF demonstrates:
- Increased LV volumes
- Greater burden of focal and diffuse fibrosis
- More RV remodeling
- Lower left atrial ejection fraction
- Higher LA volumes compared to HFpEF 3
Treatment Response Differences
The most critical clinical difference is treatment response:
- HFrEF has multiple proven therapies reducing mortality (ACE inhibitors, ARBs, beta-blockers, MRAs, ARNI, SGLT2 inhibitors)
- HFpEF historically lacked disease-modifying therapies until recent breakthrough trials with SGLT2 inhibitors (EMPEROR-Preserved, DELIVER) showing reduced cardiovascular death and HF hospitalizations 5, 4
Prognosis
Despite different pathophysiology, composite event rates (all-cause mortality and/or HF hospitalization) are similar between HFpEF and HFrEF, though HFrEF tends to present earlier (average 6.6 years vs 8.3 years to diagnosis) 3, 7.
Clinical Pitfall
The intermediate group (HFmrEF, LVEF 41-49%) represents a dynamic trajectory—patients may be improving from HFrEF or deteriorating toward it. Therefore, a single EF measurement is inadequate; serial assessments and understanding the trajectory are essential for proper classification and treatment 1, 9.