Post-Capillary Pulmonary Hypertension: Definition and Clinical Significance
Post-capillary pulmonary hypertension is defined as a mean pulmonary arterial pressure (PAPm) ≥25 mmHg with a pulmonary arterial wedge pressure (PAWP) >15 mmHg, representing pulmonary hypertension primarily caused by left heart disease. 1
Hemodynamic Classification
Post-capillary PH can be further classified into two distinct subtypes based on hemodynamic parameters:
Isolated post-capillary PH (Ipc-PH):
- Diastolic pressure gradient (DPG) <7 mmHg and/or
- Pulmonary vascular resistance (PVR) ≤3 Wood Units (WU) 1
Combined post-capillary and pre-capillary PH (Cpc-PH):
- DPG ≥7 mmHg and/or
- PVR >3 WU 1
This distinction is clinically important as it reflects different pathophysiological mechanisms and has implications for treatment approaches and prognosis.
Pathophysiology
Post-capillary PH develops through the following mechanisms:
Initial mechanism: Passive backward transmission of elevated left heart filling pressures into the pulmonary venous circulation 1, 2
Contributing factors:
- LV diastolic dysfunction
- Exercise-induced mitral regurgitation
- Loss of left atrial compliance 1
In Cpc-PH: Additional components develop beyond passive congestion:
These changes result in a further increase in PAPm beyond what would be expected from elevated PAWP alone, leading to pulmonary vascular disease, increased right ventricular afterload, and eventual right ventricular failure 1, 4.
Clinical Classification
Post-capillary PH corresponds primarily to Group 2 in the clinical classification of pulmonary hypertension 1, 5:
- Group 2: PH due to left heart disease
- Left ventricular systolic dysfunction
- Left ventricular diastolic dysfunction
- Valvular heart disease
- Congenital/acquired left heart inflow/outflow tract obstruction
- Congenital/acquired pulmonary vein stenosis
Some cases in Group 5 (PH with unclear and/or multifactorial mechanisms) may also present with post-capillary hemodynamics 5.
Diagnostic Approach
The gold standard for diagnosis is right heart catheterization, which allows for:
- Measurement of PAPm (≥25 mmHg)
- Confirmation of PAWP >15 mmHg
- Calculation of DPG and PVR to differentiate between Ipc-PH and Cpc-PH 1, 5
Clinical Significance and Prognosis
- Post-capillary PH is the most common form of pulmonary hypertension 2, 6
- Presence of PH in left heart disease results in:
- More severe symptoms
- Worse exercise tolerance
- Negative impact on overall outcome 1
- Cpc-PH (12-13% of PH due to left heart disease) carries a worse prognosis than Ipc-PH, with:
Treatment Approach
Treatment should focus on the underlying left heart disease 2, 6:
- Guideline-directed medical therapy for heart failure
- Surgical or percutaneous management of valvular disorders
- Control of modifiable risk factors and comorbidities
PAH-specific therapies (phosphodiesterase-5 inhibitors, endothelin receptor antagonists, prostanoids) are NOT recommended for post-capillary PH and may be harmful. 5, 6
Key Clinical Considerations
- Post-capillary PH patients are often older, female, with a higher prevalence of cardiovascular comorbidities 1
- The DPG appears to be the most reliable parameter for determining pulmonary vascular disease, as it is less influenced by PAWP at any level of stroke volume 1
- Referral to centers with advanced heart and pulmonary teams has shown to improve morbidity and mortality 2
- Exercise testing reveals that patients with Cpc-PH develop more severe lung congestion, arterial hypoxemia, and impaired oxygen delivery compared to those with Ipc-PH 4
Understanding the distinction between pre-capillary and post-capillary PH is crucial for appropriate treatment decisions and prognostication.