Every few years the experts in the field of pulmonary hypertension meet and update the guidelines regarding the diagnosis and treatment of pulmonary hypertension. The updated system is described below and reflects changes in the way that we think about PH.
There are five broad groups of pulmonary hypertension. Each of these groups is subdivided into smaller groups.
World Health Organization Pulmonary Hypertension Groups
1. Pulmonary Arterial Hypertension
2. Pulmonary Hypertension due to left heart disease
3. Pulmonary Hypertension due to lung disease
4. Pulmonary Hypertension due to blood clots in the lungs
5. Blood and other rare disorders that lead to Pulmonary Hypertension
Unfortunately, we are sometimes less than precise when we talk about pulmonary hypertension and the use of PH to describe a specific group can be confusing.
Pulmonary Arterial Hypertension (Group 1)
PAH specifically refers to this group. Diagnosis requires a heart catheterization and a battery of other tests to exclude left heart disease, lung disease and other rare disorders. We subdivide group 1 into four smaller groups.
1. Idiopathic PAH
2. Heritable (genetic causes that may be passed to your children)
a. BMPR2 (the most common cause of PAH that runs in families)
b. ALK1, endoglin, SMAD9, CAV1, KCNK3 (less common genetic causes of PAH that runs in families)
3. Drug and Toxin induced
a. Amphetamines and Methamphetamines
c. Fenfluramine-Phentermine (prescription diet pills sold in the 1980’s and 1990’s)
4. Associated with other systemic diseases
a. Connective tissue diseases such as scleroderma, systemic lupus erythematosis, mixed connective tissue disease and rheumatoid arthritis
b. HIV infection
c. Portal hypertension (a type of liver disease that leads to high pressures within the liver)
d. Congenital heart disease
There are two rare diseases that can be very hard to distinguish from PAH and they are included at the end of the PAH classification. These are pulmonary veno-occlusive disease (PVOD) and pulmonary capillary hemangiomatosis (PCH). Although these two diseases may be hard to distinguish from PAH by diagnostic testing, in general they do not respond to the treatments for PAH and urgent lung transplantation is the best option.
Lastly, newborns may have PAH. When present from birth, it is called persistent pulmonary hypertension of the newborn (PPHN). This disorder behaves differently than other causes of PAH and is treated with oxygen and inhaled nitric oxide. Many infants do very well and have resolution of this problem.
Pulmonary Hypertension due to Left Heart Disease (Group 2)
Unlike PAH (Group 1), this group of disorders is characterized by problems on the left side of the heart. The pulmonary arteries are normal initially. Passive elevation in the pressures of the pulmonary arteries is required to achieve forward flow. Unfortunately over time, longstanding left heart disease can lead to changes within the pulmonary arteries. See my discussion on Diastolic Heart Failure. Specific subgroups within Group 2 are listed below.
1. Left ventricular systolic dysfunction (the squeeze of the left ventricle is impaired)
2. Left ventricular diastolic dysfunction (stiffness of the left ventricle leads to pressure elevation in the pulmonary arteries)
3. Valvular heart disease (either narrowing or leakiness of the left heart valves)
4. Left heart inflow and outflow obstructions not due to valvular disease and congenital cardiomyopathies (problems with blood flowing into or out of the left side of the heart not due to a valve problem)
Treatment of Group 2 PH (caused by left heart disease) focuses on the underlying problems. In patients with impaired squeeze of the left ventricle we have a group of medications that improves the left heart function over time. Patients with stiffness of the left side of the heart are treated with diuretics, blood pressure medications if their blood pressure is elevated, weight loss if they are over weight, and CPAP if they have sleep apnea. Patients with valvular heart disease are often treated with surgery to replace the diseased heart valve. Medicines are used to treat fluid retention.
Pulmonary Hypertension due to Lung Disease (Group 3)
This large and diverse group of diseases share in common that the primary problem is within the lungs or the control of lung function. The two most common diseases in this group are chronic obstructive pulmonary disease (COPD) that includes emphysema and chronic bronchitis and lung diseases that lead to scarring in the lungs or pulmonary fibrosis.
1. Chronic obstructive pulmonary disease (COPD)
2. Interstitial lung diseases (scarring and inflammation in the lungs)
3. Sleep-disordered breathing (sleep apnea)
4. Alveolar hypoventilation disorders (diseases that lead to inadequate breathing and increased levels of carbon dioxide in the blood)
5. Chronic high altitude exposure
6. Developmental abnormalities of the lung
Treatment of this group of diseases focuses on improving lung function, restoring normal sleep breathing and avoidance of high altitude. Click here for a detailed discussion about COPD and pulmonary fibrosis and pulmonary hypertension.
Chronic Thromboembolic Pulmonary Hypertension (CTEPH) (Group 4)
In this group, blood clots either launch into the lungs or form within the lungs causing pulmonary hypertension by blocking the flow of blood through the pulmonary arteries. Please see the detailed discussion about CTEPH on its own pages.
Pulmonary Hypertension with Unclear or Multifactorial Mechanisms (Group 5)
There are a handful of rare disorders that lead to pulmonary hypertension. For most of the diseases in this group, the mechanisms of PH are poorly understood.
1. Hematologic Disorders (certain types of anemia, myeloproliferative disorders and splenectomy)
2. Systemic Disorders that have lung involvement (Sarcoidosis, Langerhan cell histiocytosis, neurofibromatosis, vasculitis, and lymphangioleimyomatosis)
3. Metabolic Disorders (rare diseases of impaired cell metabolism, thyroid disease)
4. Other diseases not well classified elsewhere (such as chronic renal failure, tumors obstructing the pulmonary arteries and other rare diseases)
Treatment of Group 5 PH is directed towards optimizing the underlying disease process. We will be featuring content about Group 5 PH in the future.