PH classification has been mainly based on clinical factors, and the most recent scheme is the Dana Point Classification of 2008 established at the 4th World Congress on Pulmonary Hypertension (Table 80.1) (1), which included both adult and pediatric patients and used the same pulmonary arterial hypertension (PAH) definition for both: mean pulmonary artery pressure ≥25 mm Hg, pulmonary capillary wedge pressure ≤15 mm Hg, and an increased pulmonary vascular resistance (PVR).

In this classification system, Group 1 encompasses etiologies of primary PH and includes idiopathic, familial, and anorexigen medication-induced PH. Idiopathic pulmonary arterial hypertension (IPAH) is the most common category in this group and is diagnosed when a patient has no family history of PH, mutations associated with hereditable PAH (HPAH), or identified PAH risk factors. PAH secondary to congenital heart disease and persistent pulmonary hypertension of the newborn (PPHN) are also included in Group 1. Groups 2, 3, 4, and 5 comprise what was historically designated as secondary PH. Group 2 describes patients with PH secondary to left-sided heart disease. Patients in this category often initially have pulmonary venous hypertension with elevated pulmonary arterial pressures (PAPs) with normal pulmonary vascular resistive indices (PVRI). Over time, remodeling of the pulmonary vasculature can lead to increased PVRI. An important subgroup of these patients have PAP elevated out of proportion to the degree of left atrial hypertension and PVRI increase. Group 3 includes patients with PH secondary to lung disease (parenchymal or interstitial) or hypoxia. Hypoxia may be due to chronic upper airway obstruction, such as obstructive sleep apnea, or from low oxygen tension associated with living at high altitude. Group 4 describes patients with chronic thromboembolic PH. Pulmonary arteries are initially obstructed by either thrombus or embolus, and in some patients, there is incomplete resolution of the obstruction, leading to PH. Group 5 is a heterogeneous group of patients with PH from unclear or multifactorial etiologies.

In 2011, a new classification system was proposed that divided pediatric PH patients into 10 categories (Table 80.2, modification of Panama Classification) (2). This system attempts to incorporate mechanisms of PH seen more frequently in pediatric patients such as abnormalities of pulmonary development and postnatal pulmonary maladaptation. Notably, the Panama Classification uses the term “pulmonary hypertensive vascular disease” rather than “pulmonary hypertension” to specifically exclude children who have PH without increased PVR such as patients with systemic-to-pulmonary shunts. This distinction was made because the treatment of PH secondary to systemic-to-pulmonary shunt is closure of the shunt rather than treatment specifically targeting PAH.

Patients with PH are also classified by measures of the limits the disease places on the individual. This functional classification, such as used by the New York Heart Association (NYHA) system (3), has been shown to be a strong predictor of mortality in adult patients and is an important factor in choice of PAH therapy in both adults and children. However, adult classification systems are often less than ideal for use in children with PH, as several of the etiologies seen in children are not adequately considered, nor are developmental factors. Consequently, the Pediatric Task Force meeting in Panama also proposed an extensive functional classification based on age, physical growth, and maturation (4).