What is the classification of heart failure?

Classification of Heart Failure

Two Complementary Classification Systems

Heart failure is classified using two distinct but complementary systems: the ACC/AHA staging system (Stages A-D) that reflects disease progression, and the NYHA functional classification (Classes I-IV) that assesses current symptom severity. 1

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ACC/AHA Staging System (Stages A-D)

This staging system reflects the progressive nature of heart failure and patients typically advance forward through stages without reversal, even when symptoms improve with treatment. 1

Stage A: At Risk for Heart Failure

• Patients with risk factors for heart failure but no structural heart disease, no symptoms, and no elevated biomarkers 1
• Examples include patients with hypertension, diabetes, coronary artery disease, or family history of cardiomyopathy 1

Stage B: Pre-Heart Failure (Structural Disease Without Symptoms)

• No current or previous symptoms of heart failure but evidence of:
  • Structural heart disease (LV hypertrophy, chamber dilation, wall motion abnormalities, valvular disease) 1
  • Elevated natriuretic peptides (BNP/NT-proBNP) 1
  • Elevated cardiac troponin (in absence of acute coronary syndrome, CKD, pulmonary embolus) 1
  • Evidence of increased filling pressures by invasive hemodynamics or noninvasive imaging 1

Stage C: Symptomatic Heart Failure

• Structural heart disease with current or previous symptoms of heart failure 1
• Critical point: Once a patient reaches Stage C, they remain Stage C even if symptoms resolve with treatment (though they may return to NYHA Class I) 1
• Patients whose symptoms completely resolve with full resolution of structural abnormalities are considered to have "heart failure in remission" (though this is uncommon) 1

Stage D: Advanced Heart Failure

• Marked symptoms that interfere with daily life and recurrent hospitalizations despite optimal guideline-directed medical therapy 1
• Requires evaluation for advanced therapies: mechanical circulatory support, cardiac transplantation, or palliative care 1, 2

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NYHA Functional Classification (Classes I-IV)

This classification assesses current symptom severity and can change frequently in response to treatment or disease progression. 1 It is subjective and determined by clinician assessment. 1, 3

NYHA Class I: No Limitation

• No limitation of physical activity 3
• Ordinary physical activity does not cause symptoms of heart failure 3
• Corresponds to asymptomatic patients 1

NYHA Class II: Slight Limitation

• Slight limitation of physical activity 3
• Comfortable at rest, but ordinary physical activity results in symptoms 3
• Symptoms with moderate exertion 1

NYHA Class III: Marked Limitation

• Marked limitation of physical activity 3
• Comfortable at rest, but less than ordinary activity causes symptoms 3
• Symptoms with minimal exertion 1

NYHA Class IV: Symptoms at Rest

• Unable to carry on any physical activity without symptoms 3
• Symptoms present at rest 1, 3
• Corresponds to ACC/AHA Stage D (advanced heart failure) 2, 4

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Classification by Left Ventricular Ejection Fraction (LVEF)

LVEF classification is critical because it determines prognosis and guides treatment selection, as most clinical trials enrolled patients based on ejection fraction. 1

HFrEF: Heart Failure with Reduced Ejection Fraction

• LVEF ≤40% 1, 5, 6
• Most randomized controlled trials demonstrating survival benefit enrolled patients with LVEF ≤35% or ≤40% 1

HFmrEF: Heart Failure with Mildly Reduced Ejection Fraction

• LVEF 41-49% 1, 5, 6
• Patients are often in a dynamic trajectory: either improving from HFrEF or deteriorating toward HFrEF 1
• One measurement at one time point is inadequate—trajectory over time and underlying cause must be evaluated 1

HFpEF: Heart Failure with Preserved Ejection Fraction

• LVEF ≥50% 1, 5, 6
• Represents at least 50% of the heart failure population with increasing prevalence 1
• Diagnosis requires classic signs/symptoms of heart failure plus additional objective measures of cardiac dysfunction to improve diagnostic specificity 1

HFimpEF: Heart Failure with Improved Ejection Fraction

• Baseline LVEF ≤40%, ≥10-point increase from baseline, and second measurement >40% 5, 6
• This newer category recognizes patients whose ejection fraction has improved with treatment 5, 6

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Key Clinical Pitfalls and Caveats

Common Misunderstandings

• The ACC/AHA stage does NOT change with symptom improvement: A Stage C patient who becomes asymptomatic with treatment remains Stage C (though they become NYHA Class I) 1
• NYHA classification is highly subjective with poor reproducibility and substantial overlap in objective measures between classes 1, 7
• Mortality at 20 months for NYHA Class II ranges from 7-15% across trials, while Class III ranges from 12-26%, demonstrating poor discrimination 7

Diagnostic Requirements

• Always measure ejection fraction to determine if symptoms are due to systolic dysfunction or another cause 1
• For HFmrEF and HFpEF diagnosis, additional objective measures beyond symptoms and LVEF are required (elevated natriuretic peptides, evidence of elevated filling pressures, structural abnormalities) 1

Treatment Implications

• All patients with HFrEF should receive guideline-directed medical therapy (ACE inhibitors/ARBs, beta-blockers, mineralocorticoid receptor antagonists) regardless of NYHA class, as these provide similar relative mortality reductions across all functional classes 2, 4
• The NYHA classification determines eligibility for certain interventions but should be supplemented with objective measures (NT-proBNP, 6-minute walk distance, quality of life scores, cardiopulmonary exercise testing) 2, 4

Documentation Requirements

• Document NYHA class at baseline and reassess after each treatment adjustment throughout the continuum of care 1, 4
• Recognize that NYHA class can change rapidly and should guide treatment intensity 4