Heart Failure Characterization
Heart failure characterization is fundamentally defined by three key elements: clinical syndrome identification (symptoms and signs), demonstration of underlying cardiac structural/functional abnormality, and classification by both ejection fraction phenotype and disease stage. 1
Core Definition
Heart failure is a clinical syndrome characterized by typical symptoms (dyspnea, fatigue, ankle swelling) that may be accompanied by signs (elevated jugular venous pressure, pulmonary crackles, peripheral edema) caused by structural and/or functional cardiac abnormality, resulting in reduced cardiac output and/or elevated intracardiac pressures at rest or during stress. 1 This definition requires corroboration by elevated natriuretic peptide levels and/or objective evidence of pulmonary or systemic congestion. 2, 3
A critical pitfall: Heart failure is not equivalent to cardiomyopathy or left ventricular dysfunction—these describe possible structural reasons for HF, but HF itself is a clinical diagnosis requiring both symptoms/signs AND objective cardiac abnormalities. 1
Classification by Ejection Fraction
The most widely used characterization system stratifies patients by left ventricular ejection fraction (LVEF):
- HFrEF (Heart Failure with Reduced EF): LVEF ≤40% 1, 2
- HFmrEF (Heart Failure with Mid-range EF): LVEF 41-49% 1, 2
- HFpEF (Heart Failure with Preserved EF): LVEF ≥50% 1, 2
- HFimpEF (Heart Failure with Improved EF): Baseline LVEF ≤40% with ≥10-point increase and second measurement >40% 2, 3
This ejection fraction-based classification is essential because different phenotypes have distinct underlying etiologies, demographics, comorbidities, and most importantly, different responses to therapies—only HFrEF has proven mortality-reducing treatments. 1
Staging System
Heart failure characterization includes a four-stage progression system that captures the continuum from risk to advanced disease:
Stage A (At-Risk): Patients at risk for HF without current/prior symptoms, signs, structural heart disease, or biomarker evidence 1, 2, 3
Stage B (Pre-HF): Asymptomatic patients with structural heart disease, abnormal cardiac function, or elevated natriuretic peptides but no prior HF symptoms 1, 2, 3
Stage C (Symptomatic HF): Patients with current or past symptoms/signs of HF associated with structural heart disease 1, 2, 3
Stage D (Advanced HF): Patients with severe symptoms at rest, recurrent hospitalizations despite guideline-directed therapy, requiring specialized treatments (mechanical circulatory support, continuous inotropes, transplantation, or hospice care) 1, 2, 3
Key clinical insight: The staging system is progressive—patients advance through stages with worsening prognosis, though disease course can be arrested or potentially reversed at any stage. 1
Functional Classification
The New York Heart Association (NYHA) functional classification provides symptom-based characterization:
- Class I: Cardiac disease without limitation of physical activity; ordinary activity does not cause symptoms 1
- Class II: Slight limitation of physical activity; comfortable at rest but ordinary activity causes symptoms 1
- Class III: Marked limitation of physical activity; comfortable at rest but less-than-ordinary activity causes symptoms 1
- Class IV: Inability to carry on any physical activity without discomfort; symptoms present at rest 1
Important distinction: NYHA class describes current functional status and can fluctuate, while staging describes structural disease progression and is unidirectional. A Stage C patient may be NYHA Class I with optimal therapy. 1
Etiologic Characterization
Complete heart failure characterization requires identifying the underlying cause:
- Ischemic cardiomyopathy: Accounts for approximately 40% of HF cases globally, with significant geographic variation (49-54% in Western populations) 4, 5
- Hypertensive heart disease: Underlying cause in 17-31% of cases, more prevalent in HFpEF 4, 5
- Idiopathic dilated cardiomyopathy: Approximately 30% of cases, with up to 30% having genetic causes 4, 5
- Valvular disease: 8-20% of cases, higher in HFpEF (20%) versus HFrEF (4%) 5
- Other causes: Include toxic/metabolic (alcohol, chemotherapy), infectious (viral myocarditis, Chagas disease), peripartum cardiomyopathy, and infiltrative diseases 1, 5
Clinical imperative: Identifying the specific etiology is crucial because precise pathology determines specific treatment (e.g., valve repair for valvular disease, rate control for tachycardia-induced cardiomyopathy). 1
Diagnostic Requirements
Heart failure characterization requires integration of multiple data elements:
Clinical assessment: History focusing on dyspnea, fatigue, exercise intolerance, fluid retention; physical examination for elevated jugular venous pressure, pulmonary rales, peripheral edema 1
Biomarkers: Elevated natriuretic peptides (BNP or NT-proBNP) are essential for diagnosis confirmation 1, 6, 2
Cardiac imaging: Echocardiography is the primary modality for assessing ventricular function, measuring LVEF, identifying structural abnormalities, and evaluating diastolic function 1, 6
Laboratory tests: Sodium, potassium, renal function (creatinine, BUN), complete blood count, thyroid function 1
Critical point: No single test diagnoses heart failure—it requires clinical syndrome recognition plus objective demonstration of cardiac abnormality. 1
Hemodynamic and Metabolic Characterization
Advanced characterization may include:
Cardiopulmonary exercise testing (CPET): Reveals metabolic and hemodynamic alterations during stress that may be silent at rest, particularly valuable in HFpEF 7
Exercise stress echocardiography: Assesses cardiac structure and function during physiologic stress 7
Invasive hemodynamics: Right and left heart catheterization for elevated filling pressures, cardiac output assessment 1
These advanced assessments help identify disease trajectories and risk factors, especially in early or preserved ejection fraction phenotypes where resting abnormalities may be subtle. 7