What are the definitions of the ACC/AHA stages of heart failure and the NYHA functional classification?

Heart Failure Staging and Classification Systems

ACC/AHA Staging System (Stages A–D)

The ACC/AHA developed a four-stage classification that emphasizes the unidirectional progression of heart failure, where patients advance forward through stages but cannot revert to earlier stages even if symptoms improve. 1

Stage A: At Risk for Heart Failure

• Patients have risk factors but no structural heart disease, no symptoms, and no cardiac biomarker elevation. 2
• Risk factors include hypertension, coronary artery disease, diabetes mellitus, metabolic syndrome, obesity, exposure to cardiotoxic drugs or alcohol, and family history of cardiomyopathy. 1, 2
• These patients have never had structural cardiac abnormalities, LV dysfunction, hypertrophy, or geometric chamber distortion. 1

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

• Patients have structural cardiac abnormalities but have never experienced heart failure symptoms. 2
• Structural abnormalities include LV hypertrophy, LV fibrosis, ventricular dilatation or hypocontractility, reduced LV or RV function, asymptomatic valvular disease, prior myocardial infarction, elevated filling pressures, or elevated cardiac biomarkers. 2
• This represents "a point of no return, unless progression of the disease is slowed or stopped by treatment." 3

Stage C: Symptomatic Heart Failure

• Patients have current or past heart failure symptoms together with underlying structural heart disease. 1, 2
• Once a patient experiences symptoms, they remain classified as Stage C permanently, regardless of subsequent symptom resolution or treatment response. 2
• This stage encompasses the bulk of patients with heart failure in clinical practice. 1
• Stage C patients can have any NYHA functional class (I-IV) depending on their current symptom severity. 3

Stage D: Advanced Heart Failure

• Patients have advanced structural disease with marked symptoms at rest despite maximal medical therapy, requiring specialized interventions. 2
• Specialized interventions include mechanical circulatory support, continuous intravenous inotropes, heart transplantation, procedures to facilitate fluid removal, or hospice care. 1, 2
• Common clinical scenarios include frequent hospitalizations for decompensation, inability to be safely discharged from hospital, or awaiting transplantation. 2

NYHA Functional Classification (Classes I–IV)

The NYHA classification provides a subjective, dynamic assessment of current symptom severity that complements—but does not replace—the ACC/AHA staging system. 2

Key Distinction from ACC/AHA Staging

• NYHA classes are mutable and can improve or worsen with therapy or disease progression, whereas ACC/AHA stages progress only forward. 2
• NYHA class can change frequently over short periods of time in response to treatment. 1
• This classification primarily gauges symptom severity in patients who are in Stage C or Stage D. 1

NYHA Class I

• No limitation of physical activity; ordinary physical activity does not cause undue fatigue, palpitation, dyspnea, or anginal pain. 2

NYHA Class II

• Slight limitation of physical activity; comfortable at rest, but ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain. 2

NYHA Class III

• Marked limitation of physical activity; comfortable at rest, but less than ordinary activity causes fatigue, palpitation, dyspnea, or anginal pain. 2

NYHA Class IV

• Unable to carry on any physical activity without discomfort; symptoms of heart failure or anginal syndrome may be present even at rest. 2

Clinical Implications and Pitfalls

Irreversibility of ACC/AHA Stages

• Treatment strategies are anchored to the stage at which structural disease is first identified, ensuring early-stage interventions are applied before irreversible remodeling occurs. 2
• A Stage C patient who becomes asymptomatic with treatment (NYHA Class I) remains Stage C and requires all Stage C therapies, never reverting to Stage B. 1

Complementary Use of Both Systems

• The ACC/AHA staging system reliably and objectively identifies patients during disease development and links treatments uniquely appropriate at each stage. 1
• NYHA class remains an independent predictor of mortality despite its subjectivity, and clinicians should document baseline NYHA class and reassess it throughout care to capture functional changes. 2

Common Pitfall

• Do not confuse improvement in NYHA class with regression of ACC/AHA stage—a patient with Stage C heart failure who improves from NYHA Class III to Class I with treatment remains Stage C and requires continued Stage C therapies. 1