Pulmonary Hypertension
Rajesh Shenoy
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Definition, Classification
Definition:
As in adults, pulmonary hypertension (PH) is present when the mean pulmonary artery pressure (mPAP) exceeds 25 mm Hg in term babies at sea level after 3 months of age.
In the context of congenital heart disease, it is important to emphasize that pulmonary hypertensive vascular disease (PHVD) may be present even when the mPAP is less than 25 mm Hg (e.g., in the low-flow situation of a cavopulmonary shunt when there is no subpulmonary ventricle). On the other hand, PHVD may not be present even when the mPAP is greater than 25 mm Hg (e.g., when there is a pulsatile source of pulmonary blood flow from a systemic-pulmonary artery shunt). Even though indexed pulmonary vascular resistance (PVRi) is not used in the definition of PH, it plays an important role in the diagnosis and management of PHVD in patients with congenital heart disease.
Pulmonary artery hypertension (PAH) is present when the mPAP exceeds 25 mm Hg, but the pulmonary artery wedge pressure is less than 15 mm Hg, though the PVRi exceeds 2 Woods Units/m2. When no underlying etiology for PAH is found, the condition is referred to as idiopathic pulmonary hypertension (IPAH).

Classification:
The WHO classification of adult PH was modified at the Fifth World Symposium for Pulmonary Hypertension, held in Nice, France. The revised clinical classification of PH groups patients into classes based on purported etiologic mechanisms (Table 1). Group 1 includes patients with pulmonary arterial hypertension secondary to genetic mutations, drugs, toxins, and infections. It also includes patients with idiopathic and heritable PAH. Separate subgroups include those with veno-occlusive disease and persistent pulmonary hypertension of the newborn. Group 2 includes patients with PH secondary to left heart disease. Patients with PH due to lung diseases, with or without hypoxia comprise Group 3. Group 4 includes patients with chronic thromboembolism. PH associated with unclear but multifactorial mechanisms forms Group 5.
Specifically, with regard to congenital heart disease, the Nice modification recognizes 4 types associated with PAH (Table 2). Type 1 includes patients with classic Eisenmenger syndrome and right-to-left shunting. Type 2 includes patients with PHVD secondary to a large left-to-right shunt. Type 3 includes patients with PAH and co-incidental CHD, while type 4 includes patients with repaired CHD who develop PAH in the post-operative period. It is important to remember that patients without a subpulmonary ventricle, who do not meet the criteria for PH, remain at risk for pulmonary vascular disease, and are not represented in this classification.
The Nice classification is adult-focused, and may not truly reflect the heterogeneity of neonatal and pediatric PH. The pediatric task force of the Pulmonary Vascular Research Institute proposed the Panama Classification of PHVD in the pediatric population (Table 3), that highlights the phenotypic heterogeneity in this patient population.

Table 1: WHO Classification of Pulmonary Hypertension
1. PAH
  • 1.1 Idiopathic
  • 1.2 Heritable
  • 1.3 Drug and toxin induced
  • 1.4 APAH
1' PVOD and/or PCH
1.1" PPHN
2. PH due to left-sided heart disease
  • 2.1 LV systolic dysfunction
  • 2.2 LV diastolic dysfunction
  • 2.3 Valvular disease
  • 2.4 Congenital/acquired left heart inflow/outflow tract obstruction and congenital cardiomyopathy
3. PH caused by lung disease or hypoxemia
  • 3.1 Chronic obstructive pulmonary edema
  • 3.2 Interstitial lung disease<
  • 3.3 Other pulmonary diseases with mixed restrictive and obstructive pattern
  • 3.4 Sleep-disordered breathing
  • 3.5 Alveolar hypoventilation syndromes
  • 3.6 Long-term exposure to high altitudes
  • 3.7 Developmental lung diseases
4. Chronic thromboembolic disease
5. PH with unclear or multifactorial mechanisms
  • 5.1 Hematological disorders: chronic hemolytic anemia, myeloproliferative disorders, splenectomy
  • 5.2 Systemic disorders: sarcoidosis, pulmonary histiocytosis, lymphangioleiomyomatosis
  • 5.3 Metabolic disorders: glycogen storage disease, Gaucher disease, thyroid disorders
  • 5.4 Others: tumor obstruction, fibrosing mediastinitis, chronic renal failure, segmental PH



Table 2: Classification of PAH associated with congenital heart disease
1. Eisenmenger syndrome
2. Left-to-right shunts
  • a. Operable
  • b. Inoperable
3. PAH with co-incidental CHD
4. Post-operative PAH



Table 3: Panama Classification of PHVD in the Pediatric Population
Prenatal or developmental PH vascular disease
Perinatal pulmonary vascular maladaptation
Pediatric cardiovascular disease
Bronchopulmonary dusplasia
Isolated pediatric pulmonary hypertensive vascular disease
Multifactorial pulmonary hypertensive vascular disease in congenital malformation syndromes
Pediatric lung disease
Pediatric thromboembolic disease
Pediatric hypobaric hypoxic exposure
Pediatric pulmonary vascular diseases associated with other system disorders




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