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Secondary pulmonary hypertension (PH) refers to any type of PH that is caused by an underlying health condition. This is in contrast to primary PH, which has an unknown cause.

Normally, the right side of the heart pumps blood through to the lungs, where it picks up oxygen. The newly oxygenated blood then gets pumped back through the left side of the heart so it can carry oxygen through the rest of the body.

In someone with PH, however, blood cannot properly flow through the pulmonary arteries (blood vessels in the lungs). This results in the right side of the heart working extra hard to pump blood, leading to high blood pressure and enlargement of the right side of the heart. Ultimately, this condition can result in right heart failure.

Types of Pulmonary Hypertension

Although PH was originally classified as either primary or secondary, those terms are no longer widely used. Instead, the World Health Organization (WHO) now divides PH into five different groups depending on the cause:

• Group 1 — Pulmonary arterial hypertension (PAH), which is most commonly idiopathic (has an unknown cause) but can also have other causes such as genetic factors, certain drugs, or connective tissue disease
• Group 2 — PH related to heart disease
• Group 3 — PH related to lung disease
• Group 4 — PH caused by blood clotting disorders
• Group 5 — PH with poorly understood association to other disorders

Idiopathic pulmonary arterial hypertension (IPAH), included in group 1, might also be referred to as primary PH. All other forms of PH can be considered secondary PH.

Causes of Pulmonary Hypertension

Many conditions can lead to PH. Typically, it is a form of heart or lung disease. However, there are additional genetic risk factors, exposures, and other chronic conditions that are associated with PH.

Connective Tissue Diseases

Organs and tissues throughout the body are supported by connective tissue, which helps provide structure. The connective tissue can be affected by several autoimmune disorders caused by the immune system inappropriately attacking the tissue. Conditions that can lead to PH include:

• Scleroderma — A disease that causes scar tissue to form on the skin and organs
• Systemic lupus erythematosus — Also known as lupus, causes inflammation in organs throughout the body
• Mixed connective tissue disease — A complex disease that shares features with lupus, scleroderma, and rheumatoid arthritis

PAH as a complication of connective tissue diseases is included in group 1 PH.

Genetic Factors

Mutations in certain genes are associated with an increased risk of PH. Genetic mutations can be inherited, which can cause PH to be more prevalent in some families.

HIV Infection

Another known risk factor for PH is human immunodeficiency virus (HIV) infection. HIV can directly cause PH similar to other causes of group 1 PH or cause lung disease and other health problems that may lead to the development of PH.

Liver Disease

High pressure in the liver caused by portal hypertension is linked to PH. This cause falls into the group 1 category.

Heart Disease

PH is often associated with chronic heart disease. In some cases, this is congenital heart disease, which is a condition present at birth. PH associated with congenital heart disease is part of group 1.

One of the most common causes of PH is left heart disease, which causes a buildup of pressure in the pulmonary arteries due to left-side heart dysfunction. PH associated with left heart disease makes up the group 2 classification. It may also be called pulmonary venous hypertension or postcapillary PH.

Chronic Lung Disease

Conditions that negatively affect lung function can also cause PH. PH-associated lung diseases include:

• Interstitial lung disease
• Chronic pulmonary obstructive disease (often referred to as COPD)
• Sleep apnea, or improper breathing during sleep
• Chronic high altitude exposure
• Physical abnormalities of the lungs
• Alveolar hypoventilation disorder, which causes high levels of carbon dioxide in the blood due to poor breathing

Some of these conditions can cause pulmonary fibrosis, a lung disease that occurs from tissue damage and scarring. PH caused by lung diseases corresponds to the group 3 category.

Blood Clots

The group 4 classification includes chronic thromboembolic PH, which is PH caused by blood clots. In many cases, this is due to an acute pulmonary embolism, which occurs when a blood clot from a deep vein in the leg breaks off and travels to the lungs. In a small subset of patients with acute pulmonary embolism, the blood clots do not dissolve. Over time, this can lead to an increase in pulmonary artery pressure.

Rare Conditions

The group 5 category includes other rare diseases that are linked to PH in a way that isn’t well understood. Conditions in this category include:

• Metabolic disorders, which are abnormal chemical reactions that disrupt the way the body transforms food into energy and gets rid of waste
• Hematologic diseases, which affect the levels of blood cells in the body
• Disorders that are systemic, meaning they affect the whole body, and also involve the lungs
• Kidney failure

Treatment for Secondary Pulmonary Hypertension

For secondary PH, the initial treatment approach is generally to target the underlying condition that is causing the PH. This is referred to as primary treatment.

Oftentimes, however, PH will persist despite primary treatment and more advanced therapy may be required. After a diagnosis of PH, your health care provider will determine potential underlying causes and discuss a treatment approach that best suits your condition.

Talk With Others Who Understand

MyPHTeam is the social network for people with pulmonary hypertension and their loved ones. On MyPHTeam, more than 46,000 members come together to ask questions, give advice, and share their stories with others who understand life with pulmonary hypertension.

Are you or a loved one living with secondary pulmonary hypertension? Share your experience in the comments below, or start a conversation by posting on MyPHTeam.