The Statement is Incorrect: Orthopnea and PND Do Not Define Specific NYHA Classes
The claim that orthopnea means NYHA IV and paroxysmal nocturnal dyspnea (PND) means NYHA III is fundamentally incorrect. NYHA classification is based on the degree of physical activity limitation, not on specific symptoms like orthopnea or PND 1, 2, 3.
Understanding NYHA Classification
The NYHA functional classification is determined by when symptoms occur during physical activity, not by the type of symptoms 2, 3:
- NYHA Class I: No limitation of physical activity; ordinary physical activity does not cause symptoms 2, 3
- NYHA Class II: Slight limitation of physical activity; comfortable at rest but ordinary physical activity results in symptoms 2, 3
- NYHA Class III: Marked limitation of physical activity; less than ordinary activity causes symptoms 2, 3
- NYHA Class IV: Symptoms at rest; inability to carry on any physical activity without symptoms 2, 3
Why Orthopnea and PND Don't Define NYHA Classes
Orthopnea (dyspnea when lying flat) can occur across multiple NYHA classes and is not specific to Class IV. Research demonstrates that orthopnea is present in patients with NYHA Class II-IV symptoms, with the severity correlating with increased diaphragmatic effort and worsening lung mechanics when supine 4. The study found orthopnea in patients across NYHA II-IV, not exclusively in Class IV 4.
Similarly, paroxysmal nocturnal dyspnea is not specific to NYHA Class III. Both orthopnea and PND are symptoms of volume overload and elevated filling pressures that can manifest at various stages of heart failure severity 5.
What Actually Defines Each NYHA Class
The key distinction between classes is the level of physical exertion that triggers symptoms 1, 2, 3:
- NYHA II patients develop symptoms with ordinary activities like walking on level ground or climbing one flight of stairs 2
- NYHA III patients develop symptoms with less than ordinary activity, such as walking short distances or minimal exertion 2, 3
- NYHA IV patients have symptoms at complete rest, even while sitting or lying down 2, 3
Clinical Implications
NYHA classification should be assessed based on functional capacity during physical activity, supplemented by objective measures including NT-proBNP levels, 6-minute walk distance, and cardiopulmonary exercise testing 1, 2. The presence of orthopnea or PND indicates volume overload requiring diuretic adjustment, but does not by itself determine NYHA class 4.
All patients with HFrEF (LVEF ≤35-40%) should receive guideline-directed medical therapy regardless of NYHA class, as these therapies provide similar relative mortality reductions across all functional classes 1, 2. The NYHA class helps determine eligibility for advanced interventions like cardiac resynchronization therapy (for NYHA II-IV) or evaluation for mechanical circulatory support (for NYHA IV) 1, 3.
Common Pitfall to Avoid
Do not assign NYHA class based solely on the presence of specific symptoms like orthopnea or PND. Instead, carefully assess what level of physical activity triggers dyspnea, fatigue, or other heart failure symptoms 2, 3. A patient with severe orthopnea who can still perform ordinary activities without symptoms would be NYHA Class I or II, not Class IV 1, 2.