Classifications of Heart Failure
Heart failure is classified using two complementary systems: the American College of Cardiology/American Heart Association (ACC/AHA) staging system based on disease progression and the New York Heart Association (NYHA) functional classification based on symptom severity. 1
ACC/AHA Staging System
The ACC/AHA staging system categorizes heart failure based on disease progression and structural changes:
Stage A: At Risk for HF - Patients with risk factors but without symptoms, structural heart disease, or cardiac biomarkers of stretch or injury
Stage B: Pre-HF - No symptoms or signs of HF but evidence of:
Stage C: Symptomatic HF - Structural heart disease with current or previous symptoms of heart failure 1
Stage D: Advanced HF - Marked HF symptoms that interfere with daily life and recurrent hospitalizations despite optimized guideline-directed medical therapy 1
This staging system recognizes that HF is a progressive condition and that interventions at earlier stages may reduce morbidity and mortality. Once a patient progresses to a higher stage, they cannot return to a lower stage, even if symptoms improve with treatment. 1
NYHA Functional Classification
The NYHA classification assesses symptom severity in patients with Stage C or D heart failure:
- Class I: No limitation of physical activity; ordinary activity does not cause HF symptoms 1
- Class II: Slight limitation of physical activity; comfortable at rest but ordinary activity results in HF symptoms 1
- Class III: Marked limitation of physical activity; less than ordinary activity causes HF symptoms 1
- Class IV: Unable to perform any physical activity without symptoms; symptoms present at rest 1
The NYHA classification is subjective and can change frequently over short periods with treatment or disease progression. Despite its limitations in reproducibility and validity, it remains an independent predictor of mortality. 1, 3
Classification by Left Ventricular Ejection Fraction (LVEF)
Heart failure can also be classified based on left ventricular ejection fraction:
- HFrEF (HF with reduced EF): LVEF ≤40% 1, 4
- HFmrEF (HF with mildly reduced EF): LVEF 41-49% 4
- HFpEF (HF with preserved EF): LVEF ≥50% 1, 4
- HFimpEF (HF with improved EF): Baseline LVEF ≤40%, ≥10-point increase from baseline, and second measurement >40% 4
This classification is important as treatment strategies may differ based on ejection fraction. However, recent evidence suggests that many therapies demonstrate benefit across a range of LVEF values, indicating that strict cutpoints may be somewhat arbitrary. 5
Clinical Implications
The ACC/AHA staging system and NYHA classification are complementary; the staging system identifies where patients are in the disease progression, while NYHA classification describes symptom severity. 1
A patient's NYHA class may change with treatment, but their ACC/AHA stage typically does not improve. 1
Treatment decisions are often based on both classification systems, with specific therapies recommended for different stages and functional classes. 2
Despite being widely used, the NYHA classification has substantial overlap in objective measures between classes, including NT-proBNP levels, quality of life scores, and exercise capacity. 3
Some clinicians further subdivide NYHA Class II into IIA (dyspnea after running or climbing ≥2 flights of stairs) and IIB (dyspnea after fast walking or climbing 2 flights of stairs) for more precise functional assessment. 6
Approximately half of patients with HFrEF have NYHA class II symptoms, representing a significant population where optimized treatment could substantially reduce morbidity and mortality. 7