What is the current classification of heart failure based on left ventricular ejection fraction (EF)?

Current Heart Failure Classification Based on Ejection Fraction

The 2022 AHA/ACC/HFSA guidelines establish four distinct categories of heart failure based on left ventricular ejection fraction (LVEF): HFrEF (≤40%), HFmrEF (41-49%), HFpEF (≥50%), and the newly recognized HFimpEF (previous LVEF ≤40% that improves to >40%). 1

The Four EF-Based Categories

1. HFrEF (Heart Failure with Reduced Ejection Fraction)

• LVEF ≤40% 1
• This represents the most clearly defined category with the strongest evidence base for guideline-directed medical therapy
• Associated with the highest mortality risk among the categories

2. HFmrEF (Heart Failure with Mildly Reduced Ejection Fraction)

• LVEF 41-49% 1
• Previously termed "mid-range EF" but renamed to reflect that these values are below normal
• Represents a dynamic category where patients are often transitioning either improving from HFrEF or deteriorating toward it 1
• Critical caveat: A single EF measurement is inadequate for these patients; the trajectory over time matters significantly 1

3. HFpEF (Heart Failure with Preserved Ejection Fraction)

• LVEF ≥50% 1
• Represents at least 50% of the HF population with increasing prevalence 1
• The threshold was set at ≥50% (rather than >40% or >45% used in older classifications) to better distinguish from reduced systolic function 1

4. HFimpEF (Heart Failure with Improved Ejection Fraction) - New Category

• Previous LVEF ≤40% with follow-up measurement >40% 1
• This is explicitly classified as a subgroup of HFrEF, not HFpEF 1
• Critical management point: These patients should continue HFrEF treatment even after EF improvement, as EF can decrease after medication withdrawal 1
• The committee deliberately avoided terms like "recovered EF" because cardiac structural abnormalities (LV dilatation, diastolic dysfunction) typically persist despite EF improvement 1

Key Diagnostic Requirements for HFmrEF and HFpEF

Beyond just the EF number, HFmrEF and HFpEF diagnoses require additional objective evidence of cardiac dysfunction to improve diagnostic specificity 1:

• Elevated natriuretic peptides (BNP/NT-proBNP)
• Evidence of increased LV filling pressures, demonstrated by:
  • Echocardiographic diastolic parameters (E/e' ≥15) 1
  • Invasive hemodynamic measurements at rest or exercise
  • Provocative testing (exercise, fluid challenge)
• Structural heart disease evidence:
  • Increased left atrial volume index
  • Increased LV mass index 1

This requirement addresses the reality that HF symptoms are nonspecific and overlap with other conditions, and normal natriuretic peptides don't exclude HFmrEF or HFpEF 1.

Understanding EF Trajectories

The guidelines emphasize that LVEF is not static 1, 2. Patients can move between categories based on:

• Underlying disease cause and duration
• Adherence to guideline-directed medical therapy (GDMT)
• Reexposure to cardiotoxic agents
• Natural disease progression

Important clinical implication: When a patient with HFrEF improves to LVEF >40%, they are reclassified as HFimpEF but remain on HFrEF treatment protocols because discontinuation often leads to EF decline 1.

Practical Diagnostic Algorithm

For patients with suspected HF and LVEF 41-49% or ≥50%:

1. Confirm HF symptoms and signs (dyspnea, edema, fatigue, elevated JVP)
2. Measure natriuretic peptides (elevated supports diagnosis)
3. Perform comprehensive echocardiography looking for:
   • Diastolic dysfunction (E/e' ratio)
   • Left atrial enlargement
   • LV hypertrophy
   • Pulmonary artery systolic pressure
4. If diagnosis uncertain, consider:
   • Exercise stress echocardiography with diastolic assessment 1
   • Invasive hemodynamic testing at rest or exercise 1
   • H₂FPEF score (for HFpEF specifically): incorporates obesity, atrial fibrillation, age >60, ≥2 antihypertensives, E/e' >9, and PA systolic pressure >35 mmHg; scores ≥6 indicate high likelihood of HFpEF 1

Common Pitfalls to Avoid

• Don't assume EF improvement means cure: Structural abnormalities persist, and treatment withdrawal risks EF decline 1
• Don't rely on single EF measurement for HFmrEF: Serial measurements reveal important prognostic trajectories 1
• Don't diagnose HFpEF/HFmrEF on EF alone: Require objective evidence of elevated filling pressures or structural disease 1
• Don't reclassify HFimpEF patients as HFpEF: They remain a subgroup of HFrEF requiring continued HFrEF therapy 1