Pulmonary arterial hypertension (PAH) is rare and uniformly deadly disease characterized by extensive narrowing of the pulmonary vasculature, leading to progressive increases in pulmonary vascular resistance and ensuing right heart failure.2 The underlying pathogenetic mechanisms of PAH are slowly being unraveled, but to a large degree remain poorly understood. Medial hypertrophy, intimal proliferative and fibrotic changes, perivascular inflammatory infiltrates, and thrombotic lesions are noted in the pulmonary arteries.
The nomenclature and classification of pulmonary hypertension was changed in 2009 by the World Health Organization (Table 12-1). Idiopathic PAH is now being used instead of primary pulmonary hypertension. The classification is easy to remember if we think of pulmonary hypertension as a "disease of triggers." In idiopathic or familial PAH, the trigger is a mutation or polymorphism. In PAH associated with connective tissue disease, congenital disease, HIV, anorexigens, or portal hypertension, the trigger is permissive phenotype. This will also help differentiate PAH from non-PAH etiologies. Non-PAH diseases could be triggered by high left atrial pressure (heart failure and valvular disease), hypoxia (lung disease), or emboli.
TABLE 12-1Classification of pulmonary hypertension ||Download (.pdf) TABLE 12-1 Classification of pulmonary hypertension
Pulmonary arterial hypertension
Drug- and toxin induced
Persistent pulmonary hypertension of the newborn
Associated with significant venous or capillary
Pulmonary hypertension with left heart disease
Heart failure (systolic or diastolic)
Valvular heart disease
Pulmonary hypertension associated with lung disease and/or hypoxemia
Chronic obstructive pulmonary disease
Interstitial lung disease
Alveolar hypoventilation disorder
Chronic exposure to high altitude
Pulmonary hypertension due to chronic thromboembolic disease
Pulmonary hypertension with unclear multifactorial mechanisms
Hematologic disorders: myeloproliferative disorders, splenectomy
Systemic disorders: sarcoidosis, pulmonary Langerhans cell histiocytosis: lymphangioleiomyomatosis, neurofibromatosis, vasculitis
Metabolic disorders: glycogen storage disease, Gaucher disease, thyroid disorders
Others: tumoral obstruction, fibrosing mediastinitis, chronic renal failure on dialysis
A right heart catheterization is mandatory to confirm the diagnosis of PAH (Figure 12-1). Important hemodynamic measurements that should be obtained are pulmonary wedge pressure, cardiac output, and pulmonary vascular resistance. Cardiac output in most cases is calculated by Fick method (using pulmonary artery saturation) because significant tricuspid regurgitation may alter the result of thermodilution method. Intracardiac shunting should be ruled out by saturation of the chambers. The diagnosis of PAH is defined as a mean pulmonary artery pressure ≥25 mm Hg at rest, in the setting of normal pulmonary capillary wedge pressure ≤15 mm Hg.1,2 PAH remains a diagnosis of exclusion and other factors, like heart failure or emboli, should be evaluated and ruled out.
Cardiac catheterization to assess the diagnosis and severity of PAH.