How do you classify the severity of pulmonary hypertension using the WHO classification system?

WHO Classification System for Pulmonary Hypertension

The WHO functional classification system for pulmonary hypertension categorizes patients into four classes based on the severity of their symptoms and limitations in physical activity, with Class I representing minimal symptoms and Class IV representing severe functional limitations.

WHO Functional Classification

The World Health Organization functional classification is a critical tool for assessing disease severity, monitoring progression, and guiding treatment decisions in pulmonary hypertension 1:

Class	Description
Class I	Patients with pulmonary hypertension but without resulting limitation of physical activity. Ordinary physical activity does not cause undue dyspnea or fatigue, chest pain, or near syncope.
Class II	Patients with pulmonary hypertension resulting in slight limitation of physical activity. They are comfortable at rest. Ordinary physical activity causes undue dyspnea or fatigue, chest pain, or near syncope.
Class III	Patients with pulmonary hypertension resulting in marked limitation of physical activity. They are comfortable at rest. Less than ordinary activity causes undue dyspnea or fatigue, chest pain, or near syncope.
Class IV	Patients with pulmonary hypertension with inability to carry out any physical activity without symptoms. These patients manifest signs of right heart failure. Dyspnea and/or fatigue may even be present at rest. Discomfort is increased by any physical activity.

Clinical Assessment Parameters

When determining WHO functional class, evaluate the following key parameters 1, 2:

1. Symptom assessment:

   • Dyspnea severity
   • Fatigue
   • Chest pain
   • Syncope or near-syncope episodes

2. Activity limitations:

   • Ability to perform ordinary daily activities
   • Exercise tolerance
   • Impact of symptoms on quality of life

3. Right ventricular function:

   • Presence of right heart failure signs
   • Fluid retention

Prognostic Implications

The WHO functional class correlates strongly with prognosis 1:

Risk Level	WHO Class	Other Prognostic Factors
Better prognosis	I-II	No clinical RV failure, slow symptom progression, no syncope, 6MWD >500m
Intermediate	III	Variable RV function, moderate symptom progression, 6MWD 165-440m
Worse prognosis	IV	Clinical RV failure, rapid symptom progression, syncope, 6MWD <300m

Assessment Timing and Follow-up

The WHO functional class should be assessed 1:

• At baseline (prior to therapy)
• Every 3-6 months during regular follow-up
• When initiating or changing therapy
• In case of clinical worsening

Common Pitfalls in Classification

1. Subjective assessment: The classification relies on subjective reporting and clinician interpretation, which may vary between providers 3.

2. Overlapping definitions: There can be difficulty distinguishing between Class II and III patients due to overlapping descriptions 3.

3. Comorbidities: Other conditions may cause similar symptoms, confounding the assessment of PH-specific limitations.

4. Adaptation: Patients may adapt their lifestyle to avoid symptoms, potentially leading to underestimation of disease severity.

To avoid these pitfalls:

• Use standardized questioning about specific activities
• Compare to previous functional status
• Consider using objective measures (6MWD, cardiopulmonary exercise testing) to supplement the classification
• Document specific examples of activities that trigger symptoms

Integration with Other Assessment Tools

For comprehensive evaluation, combine WHO functional class with 1, 2:

• 6-minute walk distance (6MWD)
• BNP/NT-proBNP levels
• Echocardiographic findings (especially RV function)
• Hemodynamic parameters (cardiac index, right atrial pressure)

This integrated approach provides a more complete picture of disease severity and prognosis than WHO class alone.