What Is the Incidence of Pulmonary Hypertension in Pediatric Patients?

Pulmonary hypertension (PH) is defined as a resting mean pulmonary artery pressure (mPAP) >25 mm Hg in children under three months of age in term infants at sea level.

In utero, pulmonary artery pressure is similar to systemic arterial pressure. After birth, pulmonary artery pressure decreases rapidly. By two to three months of postnatal age, the pressure generally achieves adult values. The annual incidence of idiopathic PH and congenital heart disease (CHD) associated PH is 0.7% and 2.2, respectively.

What Are the Causes of Pulmonary Hypertension in Pediatric Patients?

In the majority of pediatric patients, PH is idiopathic or associated with congenital heart disease. PH is classified into five major groups:

• 
  

  Group 1: PH associated with CHD. PH associated with CHD is most commonly seen among patients with large left-to-right shunts, such as a ventricular septal defect (VSD), patent ductus arteriosus (PDA), complete atrioventricular canal, truncus arteriosus, and transposition of the great arteries. The size of the shunt, the blood flow through the shunt and the location of the shunt are the most important risk factors for the development of pulmonary arterial hypertension.

  
  
• 
  

  Group 2: PH due to left-sided heart disease. Left-sided heart diseases that can lead to PH include left ventricle systolic and/or diastolic dysfunction, valvular disease, congenital/acquired left heart inflow/outflow tract obstruction, and cardiomyopathy.

  
  
• 
  

  Group 3: PH caused by chronic lung disease or hypoxemia. Chronic lung diseases that can cause PH include bronchopulmonary dysplasia (BPD), lung hypoplasia, congenital diaphragmatic hernia (CDH), or other lung lesions.

  
  
• 
  

  Group 4: PH caused by chronic thromboembolic disease.

  
  
• 
  

  Group 5: PH with unclear or multifactorial mechanisms. A combination of many rare diseases that infrequently causes PH is still seen in children.

What Is the Pathophysiology of Pulmonary Hypertension?

Increased pulmonary artery pressure (PAP) can be caused by decreased cross-sectional area of the pulmonary vascular bed. Although pulmonary veins may be the primary site of the problem, small pulmonary arteries are most affected in cases of PH. The diameter of small pulmonary arteries or veins may be narrowed by active vasoconstriction and/or pathological remodeling of small vessels through medial hypertrophy, proliferation of “neointimal cells” and deposition of connective tissues. Medial hypertrophy can resolve when the inciting stimulus is removed.

Increased PAP can also be caused by increased pulmonary blood flow (most commonly due to CHD) and/or increased pulmonary venous pressure (most commonly due to elevated left atrial pressure).

What Is a Pulmonary Hypertensive Crisis?

A PH crisis is characterized by a rapid increase in pulmonary vascular resistance (PVR) that results in pulmonary pressure exceeding systemic arterial pressure. Hypercarbia, hypoxemia, acidosis, and noxious stimuli from pain or airway manipulation can all cause a sudden increase in PVR, resulting in pulmonary hypertensive crisis and/or right heart failure. A sudden increased pulmonary pressure will compromise cardiac output from the right ventricle. Left ventricular stroke volume will also decrease, as there is limited volume available for left ventricular filling. Without rapid and effective treatment, a pulmonary hypertensive crisis can soon escalate to circulatory collapse and death.

Review the Clinical Presentation and Investigation of a Patient with PH

Persistent and/or progressive PH are commonly associated with CHD, chronic lung disease, and idiopathic/heritable PH in children. Transient PH is also relatively common in newborns with persistent pulmonary hypertension or congenital diaphragmatic hernia. Children with PH often have chromosomal abnormalities and syndromes. Children with syndromes such as Down syndrome, DiGeorge syndrome, Pierre–Robin syndrome and Noonan syndrome are commonly found to have PH.

Symptoms of PH are often similar to other less severe childhood diseases. Common presentations include fatigue, difficulty breathing, or shortness of breath with activity, dizziness, fainting, swelling in the lower extremities, or chest pain. Because the symptoms are so common, the diagnosis for childhood PH is often delayed by several months.

PH should be suspected in any child with respiratory distress, labile oxygenation, and/or cyanosis. The physical examination may be unremarkable. The primary findings on physical examination include tachypnea, retractions, grunting, desaturation unresponsive to supplemental O₂, and cyanosis. Cardiac examination may have altered heart sounds, such as a loud P2, split S2, a systolic murmur secondary to tricuspid regurgitation, or a diastolic murmur of pulmonary valve regurgitation and the signs of right heart failure, such as hepatomegaly. The initial assessments include chest X-ray, electrocardiography (ECG), and echocardiography.